From e45dd4f03ed9429a7d6b60554414d2187f2621d9 Mon Sep 17 00:00:00 2001
From: Eric Eastwood <erice@element.io>
Date: Thu, 18 Sep 2025 21:18:49 -0500
Subject: [PATCH 01/12] Split out JSON and `Clock` utilities to avoid circular
 imports

---
 synapse/util/__init__.py | 169 +--------------------------------------
 synapse/util/clock.py    | 152 +++++++++++++++++++++++++++++++++++
 synapse/util/json.py     |  57 +++++++++++++
 3 files changed, 210 insertions(+), 168 deletions(-)
 create mode 100644 synapse/util/clock.py
 create mode 100644 synapse/util/json.py

diff --git a/synapse/util/__init__.py b/synapse/util/__init__.py
index 36129c3a67b..2ae2e245a97 100644
--- a/synapse/util/__init__.py
+++ b/synapse/util/__init__.py
@@ -20,12 +20,9 @@
 #
 
 import collections.abc
-import json
 import logging
 import typing
 from typing import (
-    Any,
-    Callable,
     Dict,
     Iterator,
     Mapping,
@@ -36,17 +33,11 @@
 )
 
 import attr
-from immutabledict import immutabledict
 from matrix_common.versionstring import get_distribution_version_string
-from typing_extensions import ParamSpec
 
-from twisted.internet import defer, task
-from twisted.internet.interfaces import IDelayedCall, IReactorTime
-from twisted.internet.task import LoopingCall
+from twisted.internet import defer
 from twisted.python.failure import Failure
 
-from synapse.logging import context
-
 if typing.TYPE_CHECKING:
     pass
 
@@ -62,41 +53,6 @@ class Duration:
     DAY_MS = 24 * HOUR_MS
 
 
-def _reject_invalid_json(val: Any) -> None:
-    """Do not allow Infinity, -Infinity, or NaN values in JSON."""
-    raise ValueError("Invalid JSON value: '%s'" % val)
-
-
-def _handle_immutabledict(obj: Any) -> Dict[Any, Any]:
-    """Helper for json_encoder. Makes immutabledicts serializable by returning
-    the underlying dict
-    """
-    if type(obj) is immutabledict:
-        # fishing the protected dict out of the object is a bit nasty,
-        # but we don't really want the overhead of copying the dict.
-        try:
-            # Safety: we catch the AttributeError immediately below.
-            return obj._dict
-        except AttributeError:
-            # If all else fails, resort to making a copy of the immutabledict
-            return dict(obj)
-    raise TypeError(
-        "Object of type %s is not JSON serializable" % obj.__class__.__name__
-    )
-
-
-# A custom JSON encoder which:
-#   * handles immutabledicts
-#   * produces valid JSON (no NaNs etc)
-#   * reduces redundant whitespace
-json_encoder = json.JSONEncoder(
-    allow_nan=False, separators=(",", ":"), default=_handle_immutabledict
-)
-
-# Create a custom decoder to reject Python extensions to JSON.
-json_decoder = json.JSONDecoder(parse_constant=_reject_invalid_json)
-
-
 def unwrapFirstError(failure: Failure) -> Failure:
     # Deprecated: you probably just want to catch defer.FirstError and reraise
     # the subFailure's value, which will do a better job of preserving stacktraces.
@@ -105,129 +61,6 @@ def unwrapFirstError(failure: Failure) -> Failure:
     return failure.value.subFailure
 
 
-P = ParamSpec("P")
-
-
-@attr.s(slots=True)
-class Clock:
-    """
-    A Clock wraps a Twisted reactor and provides utilities on top of it.
-
-    Args:
-        reactor: The Twisted reactor to use.
-    """
-
-    _reactor: IReactorTime = attr.ib()
-
-    async def sleep(self, seconds: float) -> None:
-        d: defer.Deferred[float] = defer.Deferred()
-        with context.PreserveLoggingContext():
-            self._reactor.callLater(seconds, d.callback, seconds)
-            await d
-
-    def time(self) -> float:
-        """Returns the current system time in seconds since epoch."""
-        return self._reactor.seconds()
-
-    def time_msec(self) -> int:
-        """Returns the current system time in milliseconds since epoch."""
-        return int(self.time() * 1000)
-
-    def looping_call(
-        self,
-        f: Callable[P, object],
-        msec: float,
-        *args: P.args,
-        **kwargs: P.kwargs,
-    ) -> LoopingCall:
-        """Call a function repeatedly.
-
-        Waits `msec` initially before calling `f` for the first time.
-
-        If the function given to `looping_call` returns an awaitable/deferred, the next
-        call isn't scheduled until after the returned awaitable has finished. We get
-        this functionality thanks to this function being a thin wrapper around
-        `twisted.internet.task.LoopingCall`.
-
-        Note that the function will be called with no logcontext, so if it is anything
-        other than trivial, you probably want to wrap it in run_as_background_process.
-
-        Args:
-            f: The function to call repeatedly.
-            msec: How long to wait between calls in milliseconds.
-            *args: Positional arguments to pass to function.
-            **kwargs: Key arguments to pass to function.
-        """
-        return self._looping_call_common(f, msec, False, *args, **kwargs)
-
-    def looping_call_now(
-        self,
-        f: Callable[P, object],
-        msec: float,
-        *args: P.args,
-        **kwargs: P.kwargs,
-    ) -> LoopingCall:
-        """Call a function immediately, and then repeatedly thereafter.
-
-        As with `looping_call`: subsequent calls are not scheduled until after the
-        the Awaitable returned by a previous call has finished.
-
-        Also as with `looping_call`: the function is called with no logcontext and
-        you probably want to wrap it in `run_as_background_process`.
-
-        Args:
-            f: The function to call repeatedly.
-            msec: How long to wait between calls in milliseconds.
-            *args: Positional arguments to pass to function.
-            **kwargs: Key arguments to pass to function.
-        """
-        return self._looping_call_common(f, msec, True, *args, **kwargs)
-
-    def _looping_call_common(
-        self,
-        f: Callable[P, object],
-        msec: float,
-        now: bool,
-        *args: P.args,
-        **kwargs: P.kwargs,
-    ) -> LoopingCall:
-        """Common functionality for `looping_call` and `looping_call_now`"""
-        call = task.LoopingCall(f, *args, **kwargs)
-        call.clock = self._reactor
-        d = call.start(msec / 1000.0, now=now)
-        d.addErrback(log_failure, "Looping call died", consumeErrors=False)
-        return call
-
-    def call_later(
-        self, delay: float, callback: Callable, *args: Any, **kwargs: Any
-    ) -> IDelayedCall:
-        """Call something later
-
-        Note that the function will be called with no logcontext, so if it is anything
-        other than trivial, you probably want to wrap it in run_as_background_process.
-
-        Args:
-            delay: How long to wait in seconds.
-            callback: Function to call
-            *args: Postional arguments to pass to function.
-            **kwargs: Key arguments to pass to function.
-        """
-
-        def wrapped_callback(*args: Any, **kwargs: Any) -> None:
-            with context.PreserveLoggingContext():
-                callback(*args, **kwargs)
-
-        with context.PreserveLoggingContext():
-            return self._reactor.callLater(delay, wrapped_callback, *args, **kwargs)
-
-    def cancel_call_later(self, timer: IDelayedCall, ignore_errs: bool = False) -> None:
-        try:
-            timer.cancel()
-        except Exception:
-            if not ignore_errs:
-                raise
-
-
 def log_failure(
     failure: Failure, msg: str, consumeErrors: bool = True
 ) -> Optional[Failure]:
diff --git a/synapse/util/clock.py b/synapse/util/clock.py
new file mode 100644
index 00000000000..9fb3fc25096
--- /dev/null
+++ b/synapse/util/clock.py
@@ -0,0 +1,152 @@
+#
+# This file is licensed under the Affero General Public License (AGPL) version 3.
+#
+# Copyright (C) 2025 New Vector, Ltd
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# See the GNU Affero General Public License for more details:
+# <https://www.gnu.org/licenses/agpl_3.0.html>.
+#
+#
+
+
+from typing import (
+    Any,
+    Callable,
+)
+
+import attr
+from typing_extensions import ParamSpec
+
+from twisted.internet import defer, task
+from twisted.internet.interfaces import IDelayedCall, IReactorTime
+from twisted.internet.task import LoopingCall
+
+from synapse.logging import context
+from synapse.util import log_failure
+
+P = ParamSpec("P")
+
+
+@attr.s(slots=True)
+class Clock:
+    """
+    A Clock wraps a Twisted reactor and provides utilities on top of it.
+
+    Args:
+        reactor: The Twisted reactor to use.
+    """
+
+    _reactor: IReactorTime = attr.ib()
+
+    async def sleep(self, seconds: float) -> None:
+        d: defer.Deferred[float] = defer.Deferred()
+        with context.PreserveLoggingContext():
+            self._reactor.callLater(seconds, d.callback, seconds)
+            await d
+
+    def time(self) -> float:
+        """Returns the current system time in seconds since epoch."""
+        return self._reactor.seconds()
+
+    def time_msec(self) -> int:
+        """Returns the current system time in milliseconds since epoch."""
+        return int(self.time() * 1000)
+
+    def looping_call(
+        self,
+        f: Callable[P, object],
+        msec: float,
+        *args: P.args,
+        **kwargs: P.kwargs,
+    ) -> LoopingCall:
+        """Call a function repeatedly.
+
+        Waits `msec` initially before calling `f` for the first time.
+
+        If the function given to `looping_call` returns an awaitable/deferred, the next
+        call isn't scheduled until after the returned awaitable has finished. We get
+        this functionality thanks to this function being a thin wrapper around
+        `twisted.internet.task.LoopingCall`.
+
+        Note that the function will be called with no logcontext, so if it is anything
+        other than trivial, you probably want to wrap it in run_as_background_process.
+
+        Args:
+            f: The function to call repeatedly.
+            msec: How long to wait between calls in milliseconds.
+            *args: Positional arguments to pass to function.
+            **kwargs: Key arguments to pass to function.
+        """
+        return self._looping_call_common(f, msec, False, *args, **kwargs)
+
+    def looping_call_now(
+        self,
+        f: Callable[P, object],
+        msec: float,
+        *args: P.args,
+        **kwargs: P.kwargs,
+    ) -> LoopingCall:
+        """Call a function immediately, and then repeatedly thereafter.
+
+        As with `looping_call`: subsequent calls are not scheduled until after the
+        the Awaitable returned by a previous call has finished.
+
+        Also as with `looping_call`: the function is called with no logcontext and
+        you probably want to wrap it in `run_as_background_process`.
+
+        Args:
+            f: The function to call repeatedly.
+            msec: How long to wait between calls in milliseconds.
+            *args: Positional arguments to pass to function.
+            **kwargs: Key arguments to pass to function.
+        """
+        return self._looping_call_common(f, msec, True, *args, **kwargs)
+
+    def _looping_call_common(
+        self,
+        f: Callable[P, object],
+        msec: float,
+        now: bool,
+        *args: P.args,
+        **kwargs: P.kwargs,
+    ) -> LoopingCall:
+        """Common functionality for `looping_call` and `looping_call_now`"""
+        call = task.LoopingCall(f, *args, **kwargs)
+        call.clock = self._reactor
+        d = call.start(msec / 1000.0, now=now)
+        d.addErrback(log_failure, "Looping call died", consumeErrors=False)
+        return call
+
+    def call_later(
+        self, delay: float, callback: Callable, *args: Any, **kwargs: Any
+    ) -> IDelayedCall:
+        """Call something later
+
+        Note that the function will be called with no logcontext, so if it is anything
+        other than trivial, you probably want to wrap it in run_as_background_process.
+
+        Args:
+            delay: How long to wait in seconds.
+            callback: Function to call
+            *args: Postional arguments to pass to function.
+            **kwargs: Key arguments to pass to function.
+        """
+
+        def wrapped_callback(*args: Any, **kwargs: Any) -> None:
+            with context.PreserveLoggingContext():
+                callback(*args, **kwargs)
+
+        with context.PreserveLoggingContext():
+            return self._reactor.callLater(delay, wrapped_callback, *args, **kwargs)
+
+    def cancel_call_later(self, timer: IDelayedCall, ignore_errs: bool = False) -> None:
+        try:
+            timer.cancel()
+        except Exception:
+            if not ignore_errs:
+                raise
diff --git a/synapse/util/json.py b/synapse/util/json.py
new file mode 100644
index 00000000000..e6db55f8e4a
--- /dev/null
+++ b/synapse/util/json.py
@@ -0,0 +1,57 @@
+#
+# This file is licensed under the Affero General Public License (AGPL) version 3.
+#
+# Copyright (C) 2025 New Vector, Ltd
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# See the GNU Affero General Public License for more details:
+# <https://www.gnu.org/licenses/agpl_3.0.html>.
+#
+#
+
+import json
+from typing import (
+    Any,
+    Dict,
+)
+
+from immutabledict import immutabledict
+
+
+def _reject_invalid_json(val: Any) -> None:
+    """Do not allow Infinity, -Infinity, or NaN values in JSON."""
+    raise ValueError("Invalid JSON value: '%s'" % val)
+
+
+def _handle_immutabledict(obj: Any) -> Dict[Any, Any]:
+    """Helper for json_encoder. Makes immutabledicts serializable by returning
+    the underlying dict
+    """
+    if type(obj) is immutabledict:
+        # fishing the protected dict out of the object is a bit nasty,
+        # but we don't really want the overhead of copying the dict.
+        try:
+            # Safety: we catch the AttributeError immediately below.
+            return obj._dict
+        except AttributeError:
+            # If all else fails, resort to making a copy of the immutabledict
+            return dict(obj)
+    raise TypeError(
+        "Object of type %s is not JSON serializable" % obj.__class__.__name__
+    )
+
+
+# A custom JSON encoder which:
+#   * handles immutabledicts
+#   * produces valid JSON (no NaNs etc)
+#   * reduces redundant whitespace
+json_encoder = json.JSONEncoder(
+    allow_nan=False, separators=(",", ":"), default=_handle_immutabledict
+)
+
+# Create a custom decoder to reject Python extensions to JSON.
+json_decoder = json.JSONDecoder(parse_constant=_reject_invalid_json)

From bccd224489c38377ad79c66c560f60fe4662624f Mon Sep 17 00:00:00 2001
From: Eric Eastwood <erice@element.io>
Date: Thu, 18 Sep 2025 21:34:52 -0500
Subject: [PATCH 02/12] Fix imports

---
 scripts-dev/sign_json.py                                       | 2 +-
 synapse/_scripts/synapse_port_db.py                            | 3 ++-
 synapse/api/auth/mas.py                                        | 2 +-
 synapse/api/auth/msc3861_delegated.py                          | 2 +-
 synapse/api/errors.py                                          | 2 +-
 synapse/api/ratelimiting.py                                    | 2 +-
 synapse/appservice/scheduler.py                                | 2 +-
 synapse/events/builder.py                                      | 2 +-
 synapse/federation/sender/__init__.py                          | 2 +-
 synapse/federation/sender/transaction_manager.py               | 2 +-
 synapse/handlers/devicemessage.py                              | 2 +-
 synapse/handlers/e2e_keys.py                                   | 2 +-
 synapse/handlers/identity.py                                   | 2 +-
 synapse/handlers/message.py                                    | 3 ++-
 synapse/handlers/oidc.py                                       | 3 ++-
 synapse/handlers/ui_auth/checkers.py                           | 2 +-
 synapse/http/client.py                                         | 2 +-
 synapse/http/federation/matrix_federation_agent.py             | 2 +-
 synapse/http/federation/well_known_resolver.py                 | 3 ++-
 synapse/http/matrixfederationclient.py                         | 2 +-
 synapse/http/server.py                                         | 3 ++-
 synapse/http/servlet.py                                        | 2 +-
 synapse/logging/opentracing.py                                 | 2 +-
 synapse/media/_base.py                                         | 2 +-
 synapse/media/media_storage.py                                 | 2 +-
 synapse/media/oembed.py                                        | 2 +-
 synapse/media/url_previewer.py                                 | 2 +-
 synapse/module_api/__init__.py                                 | 2 +-
 synapse/replication/tcp/commands.py                            | 2 +-
 synapse/replication/tcp/external_cache.py                      | 2 +-
 synapse/replication/tcp/protocol.py                            | 2 +-
 synapse/rest/client/sync.py                                    | 2 +-
 synapse/rest/key/v2/remote_key_resource.py                     | 2 +-
 synapse/rest/well_known.py                                     | 2 +-
 synapse/server.py                                              | 2 +-
 synapse/storage/_base.py                                       | 2 +-
 synapse/storage/background_updates.py                          | 3 ++-
 synapse/storage/databases/main/account_data.py                 | 2 +-
 synapse/storage/databases/main/appservice.py                   | 2 +-
 synapse/storage/databases/main/censor_events.py                | 2 +-
 synapse/storage/databases/main/delayed_events.py               | 3 ++-
 synapse/storage/databases/main/deviceinbox.py                  | 3 ++-
 synapse/storage/databases/main/devices.py                      | 2 +-
 synapse/storage/databases/main/e2e_room_keys.py                | 2 +-
 synapse/storage/databases/main/end_to_end_keys.py              | 2 +-
 synapse/storage/databases/main/event_federation.py             | 2 +-
 synapse/storage/databases/main/event_push_actions.py           | 2 +-
 synapse/storage/databases/main/events.py                       | 2 +-
 synapse/storage/databases/main/events_bg_updates.py            | 2 +-
 synapse/storage/databases/main/lock.py                         | 2 +-
 synapse/storage/databases/main/push_rule.py                    | 3 ++-
 synapse/storage/databases/main/pusher.py                       | 2 +-
 synapse/storage/databases/main/receipts.py                     | 2 +-
 synapse/storage/databases/main/room.py                         | 2 +-
 synapse/storage/databases/main/session.py                      | 2 +-
 synapse/storage/databases/main/sliding_sync.py                 | 2 +-
 synapse/storage/databases/main/tags.py                         | 2 +-
 synapse/storage/databases/main/task_scheduler.py               | 2 +-
 synapse/storage/databases/main/ui_auth.py                      | 3 ++-
 synapse/util/async_helpers.py                                  | 2 +-
 synapse/util/batching_queue.py                                 | 2 +-
 synapse/util/caches/expiringcache.py                           | 2 +-
 synapse/util/caches/lrucache.py                                | 3 ++-
 synapse/util/caches/response_cache.py                          | 2 +-
 synapse/util/macaroons.py                                      | 3 ++-
 synapse/util/metrics.py                                        | 2 +-
 synapse/util/ratelimitutils.py                                 | 2 +-
 synapse/util/retryutils.py                                     | 2 +-
 synapse/visibility.py                                          | 2 +-
 synmark/suites/logging.py                                      | 2 +-
 tests/api/test_auth.py                                         | 2 +-
 tests/api/test_filtering.py                                    | 2 +-
 tests/api/test_urls.py                                         | 2 +-
 tests/app/test_openid_listener.py                              | 2 +-
 tests/app/test_phone_stats_home.py                             | 2 +-
 tests/appservice/test_api.py                                   | 2 +-
 tests/appservice/test_scheduler.py                             | 2 +-
 tests/config/test_room_directory.py                            | 2 +-
 tests/crypto/test_keyring.py                                   | 2 +-
 tests/events/test_auto_accept_invites.py                       | 2 +-
 tests/events/test_presence_router.py                           | 2 +-
 tests/events/test_snapshot.py                                  | 2 +-
 tests/federation/test_federation_catch_up.py                   | 2 +-
 tests/federation/test_federation_client.py                     | 2 +-
 tests/federation/test_federation_devices.py                    | 2 +-
 tests/federation/test_federation_media.py                      | 2 +-
 tests/federation/test_federation_out_of_band_membership.py     | 2 +-
 tests/federation/test_federation_sender.py                     | 2 +-
 tests/federation/test_federation_server.py                     | 2 +-
 tests/federation/transport/test_knocking.py                    | 2 +-
 tests/handlers/test_admin.py                                   | 2 +-
 tests/handlers/test_appservice.py                              | 2 +-
 tests/handlers/test_auth.py                                    | 2 +-
 tests/handlers/test_cas.py                                     | 2 +-
 tests/handlers/test_deactivate_account.py                      | 2 +-
 tests/handlers/test_device.py                                  | 2 +-
 tests/handlers/test_directory.py                               | 2 +-
 tests/handlers/test_e2e_keys.py                                | 2 +-
 tests/handlers/test_e2e_room_keys.py                           | 2 +-
 tests/handlers/test_federation.py                              | 2 +-
 tests/handlers/test_federation_event.py                        | 2 +-
 tests/handlers/test_message.py                                 | 2 +-
 tests/handlers/test_oauth_delegation.py                        | 2 +-
 tests/handlers/test_oidc.py                                    | 2 +-
 tests/handlers/test_password_providers.py                      | 2 +-
 tests/handlers/test_presence.py                                | 2 +-
 tests/handlers/test_profile.py                                 | 2 +-
 tests/handlers/test_receipts.py                                | 2 +-
 tests/handlers/test_register.py                                | 2 +-
 tests/handlers/test_room_member.py                             | 2 +-
 tests/handlers/test_room_policy.py                             | 2 +-
 tests/handlers/test_room_summary.py                            | 2 +-
 tests/handlers/test_saml.py                                    | 2 +-
 tests/handlers/test_sliding_sync.py                            | 2 +-
 tests/handlers/test_sso.py                                     | 2 +-
 tests/handlers/test_stats.py                                   | 2 +-
 tests/handlers/test_sync.py                                    | 2 +-
 tests/handlers/test_typing.py                                  | 2 +-
 tests/handlers/test_user_directory.py                          | 2 +-
 tests/handlers/test_worker_lock.py                             | 2 +-
 tests/http/test_matrixfederationclient.py                      | 2 +-
 tests/http/test_simple_client.py                               | 2 +-
 tests/http/test_site.py                                        | 2 +-
 tests/logging/test_opentracing.py                              | 2 +-
 tests/media/test_media_retention.py                            | 2 +-
 tests/media/test_media_storage.py                              | 2 +-
 tests/media/test_oembed.py                                     | 2 +-
 tests/media/test_url_previewer.py                              | 2 +-
 tests/metrics/test_phone_home_stats.py                         | 2 +-
 tests/module_api/test_account_data_manager.py                  | 2 +-
 tests/module_api/test_api.py                                   | 2 +-
 tests/module_api/test_event_unsigned_addition.py               | 2 +-
 tests/module_api/test_spamchecker.py                           | 2 +-
 tests/push/test_bulk_push_rule_evaluator.py                    | 2 +-
 tests/push/test_email.py                                       | 2 +-
 tests/push/test_http.py                                        | 2 +-
 tests/push/test_push_rule_evaluator.py                         | 2 +-
 tests/replication/_base.py                                     | 2 +-
 tests/replication/storage/_base.py                             | 2 +-
 tests/replication/storage/test_events.py                       | 2 +-
 tests/replication/tcp/streams/test_events.py                   | 2 +-
 tests/replication/tcp/streams/test_thread_subscriptions.py     | 2 +-
 tests/replication/test_auth.py                                 | 2 +-
 tests/replication/test_federation_ack.py                       | 2 +-
 tests/replication/test_federation_sender_shard.py              | 2 +-
 tests/replication/test_multi_media_repo.py                     | 2 +-
 tests/replication/test_pusher_shard.py                         | 2 +-
 tests/replication/test_sharded_event_persister.py              | 2 +-
 tests/replication/test_sharded_receipts.py                     | 2 +-
 tests/rest/admin/test_admin.py                                 | 2 +-
 tests/rest/admin/test_background_updates.py                    | 2 +-
 tests/rest/admin/test_device.py                                | 2 +-
 tests/rest/admin/test_event_reports.py                         | 2 +-
 tests/rest/admin/test_federation.py                            | 2 +-
 tests/rest/admin/test_media.py                                 | 2 +-
 tests/rest/admin/test_registration_tokens.py                   | 2 +-
 tests/rest/admin/test_room.py                                  | 2 +-
 tests/rest/admin/test_scheduled_tasks.py                       | 2 +-
 tests/rest/admin/test_server_notice.py                         | 2 +-
 tests/rest/admin/test_statistics.py                            | 2 +-
 tests/rest/admin/test_user.py                                  | 2 +-
 tests/rest/admin/test_username_available.py                    | 2 +-
 tests/rest/client/sliding_sync/test_connection_tracking.py     | 2 +-
 tests/rest/client/sliding_sync/test_extension_account_data.py  | 2 +-
 tests/rest/client/sliding_sync/test_extension_e2ee.py          | 2 +-
 tests/rest/client/sliding_sync/test_extension_receipts.py      | 2 +-
 .../client/sliding_sync/test_extension_thread_subscriptions.py | 2 +-
 tests/rest/client/sliding_sync/test_extension_to_device.py     | 2 +-
 tests/rest/client/sliding_sync/test_extension_typing.py        | 2 +-
 tests/rest/client/sliding_sync/test_extensions.py              | 2 +-
 tests/rest/client/sliding_sync/test_lists_filters.py           | 2 +-
 tests/rest/client/sliding_sync/test_room_subscriptions.py      | 2 +-
 tests/rest/client/sliding_sync/test_rooms_invites.py           | 2 +-
 tests/rest/client/sliding_sync/test_rooms_meta.py              | 2 +-
 tests/rest/client/sliding_sync/test_rooms_required_state.py    | 2 +-
 tests/rest/client/sliding_sync/test_rooms_timeline.py          | 2 +-
 tests/rest/client/sliding_sync/test_sliding_sync.py            | 2 +-
 tests/rest/client/test_account.py                              | 2 +-
 tests/rest/client/test_auth.py                                 | 2 +-
 tests/rest/client/test_capabilities.py                         | 2 +-
 tests/rest/client/test_consent.py                              | 2 +-
 tests/rest/client/test_delayed_events.py                       | 2 +-
 tests/rest/client/test_devices.py                              | 2 +-
 tests/rest/client/test_directory.py                            | 2 +-
 tests/rest/client/test_ephemeral_message.py                    | 2 +-
 tests/rest/client/test_events.py                               | 2 +-
 tests/rest/client/test_filter.py                               | 2 +-
 tests/rest/client/test_identity.py                             | 2 +-
 tests/rest/client/test_login.py                                | 2 +-
 tests/rest/client/test_login_token_request.py                  | 2 +-
 tests/rest/client/test_media.py                                | 2 +-
 tests/rest/client/test_mutual_rooms.py                         | 2 +-
 tests/rest/client/test_notifications.py                        | 2 +-
 tests/rest/client/test_owned_state.py                          | 2 +-
 tests/rest/client/test_password_policy.py                      | 2 +-
 tests/rest/client/test_power_levels.py                         | 2 +-
 tests/rest/client/test_presence.py                             | 2 +-
 tests/rest/client/test_profile.py                              | 2 +-
 tests/rest/client/test_read_marker.py                          | 2 +-
 tests/rest/client/test_receipts.py                             | 2 +-
 tests/rest/client/test_redactions.py                           | 2 +-
 tests/rest/client/test_register.py                             | 2 +-
 tests/rest/client/test_relations.py                            | 2 +-
 tests/rest/client/test_rendezvous.py                           | 2 +-
 tests/rest/client/test_reporting.py                            | 2 +-
 tests/rest/client/test_retention.py                            | 2 +-
 tests/rest/client/test_rooms.py                                | 2 +-
 tests/rest/client/test_shadow_banned.py                        | 2 +-
 tests/rest/client/test_sync.py                                 | 2 +-
 tests/rest/client/test_third_party_rules.py                    | 2 +-
 tests/rest/client/test_thread_subscriptions.py                 | 2 +-
 tests/rest/client/test_transactions.py                         | 2 +-
 tests/rest/client/test_typing.py                               | 2 +-
 tests/rest/client/test_upgrade_room.py                         | 2 +-
 tests/rest/key/v2/test_remote_key_resource.py                  | 2 +-
 tests/rest/media/test_domain_blocking.py                       | 2 +-
 tests/rest/media/test_url_preview.py                           | 2 +-
 tests/rest/synapse/mas/test_devices.py                         | 2 +-
 tests/rest/synapse/mas/test_users.py                           | 2 +-
 tests/server.py                                                | 2 +-
 tests/server_notices/__init__.py                               | 2 +-
 tests/server_notices/test_consent.py                           | 2 +-
 tests/server_notices/test_resource_limits_server_notices.py    | 2 +-
 tests/state/test_v21.py                                        | 2 +-
 tests/storage/databases/main/test_deviceinbox.py               | 2 +-
 tests/storage/databases/main/test_end_to_end_keys.py           | 2 +-
 tests/storage/databases/main/test_events_worker.py             | 2 +-
 tests/storage/databases/main/test_lock.py                      | 2 +-
 tests/storage/databases/main/test_receipts.py                  | 2 +-
 tests/storage/databases/main/test_room.py                      | 2 +-
 tests/storage/test__base.py                                    | 2 +-
 tests/storage/test_account_data.py                             | 2 +-
 tests/storage/test_appservice.py                               | 2 +-
 tests/storage/test_background_update.py                        | 2 +-
 tests/storage/test_cleanup_extrems.py                          | 2 +-
 tests/storage/test_client_ips.py                               | 2 +-
 tests/storage/test_database.py                                 | 2 +-
 tests/storage/test_devices.py                                  | 2 +-
 tests/storage/test_directory.py                                | 2 +-
 tests/storage/test_e2e_room_keys.py                            | 2 +-
 tests/storage/test_end_to_end_keys.py                          | 2 +-
 tests/storage/test_event_chain.py                              | 2 +-
 tests/storage/test_event_federation.py                         | 3 ++-
 tests/storage/test_event_push_actions.py                       | 2 +-
 tests/storage/test_events.py                                   | 2 +-
 tests/storage/test_events_bg_updates.py                        | 2 +-
 tests/storage/test_id_generators.py                            | 2 +-
 tests/storage/test_monthly_active_users.py                     | 2 +-
 tests/storage/test_profile.py                                  | 2 +-
 tests/storage/test_purge.py                                    | 2 +-
 tests/storage/test_receipts.py                                 | 2 +-
 tests/storage/test_redaction.py                                | 2 +-
 tests/storage/test_registration.py                             | 2 +-
 tests/storage/test_relations.py                                | 2 +-
 tests/storage/test_rollback_worker.py                          | 2 +-
 tests/storage/test_room.py                                     | 2 +-
 tests/storage/test_room_search.py                              | 2 +-
 tests/storage/test_roommember.py                               | 2 +-
 tests/storage/test_sliding_sync_tables.py                      | 2 +-
 tests/storage/test_state.py                                    | 2 +-
 tests/storage/test_state_deletion.py                           | 2 +-
 tests/storage/test_stream.py                                   | 2 +-
 tests/storage/test_thread_subscriptions.py                     | 2 +-
 tests/storage/test_transactions.py                             | 2 +-
 tests/storage/test_txn_limit.py                                | 2 +-
 tests/storage/test_user_directory.py                           | 2 +-
 tests/storage/test_user_filters.py                             | 2 +-
 tests/test_mau.py                                              | 2 +-
 tests/test_phone_home.py                                       | 2 +-
 tests/test_server.py                                           | 2 +-
 tests/test_state.py                                            | 2 +-
 tests/test_terms_auth.py                                       | 2 +-
 tests/test_utils/oidc.py                                       | 2 +-
 tests/test_visibility.py                                       | 2 +-
 tests/unittest.py                                              | 2 +-
 tests/util/test_expiring_cache.py                              | 2 +-
 tests/util/test_logcontext.py                                  | 2 +-
 tests/util/test_task_scheduler.py                              | 2 +-
 278 files changed, 291 insertions(+), 278 deletions(-)

diff --git a/scripts-dev/sign_json.py b/scripts-dev/sign_json.py
index 14aacf93825..40e0c529dac 100755
--- a/scripts-dev/sign_json.py
+++ b/scripts-dev/sign_json.py
@@ -30,7 +30,7 @@
 
 from synapse.api.room_versions import KNOWN_ROOM_VERSIONS
 from synapse.crypto.event_signing import add_hashes_and_signatures
-from synapse.util import json_encoder
+from synapse.util.json import json_encoder
 
 
 def main() -> None:
diff --git a/synapse/_scripts/synapse_port_db.py b/synapse/_scripts/synapse_port_db.py
index a81db3cfbfb..a4591014f4e 100755
--- a/synapse/_scripts/synapse_port_db.py
+++ b/synapse/_scripts/synapse_port_db.py
@@ -98,7 +98,8 @@
 from synapse.storage.engines import create_engine
 from synapse.storage.prepare_database import prepare_database
 from synapse.types import ISynapseReactor
-from synapse.util import SYNAPSE_VERSION, Clock
+from synapse.util import SYNAPSE_VERSION
+from synapse.util.clock import Clock
 from synapse.util.stringutils import random_string
 
 # Cast safety: Twisted does some naughty magic which replaces the
diff --git a/synapse/api/auth/mas.py b/synapse/api/auth/mas.py
index 40b4a5bd34b..ef82ea9cc77 100644
--- a/synapse/api/auth/mas.py
+++ b/synapse/api/auth/mas.py
@@ -43,9 +43,9 @@
 from synapse.metrics import SERVER_NAME_LABEL
 from synapse.synapse_rust.http_client import HttpClient
 from synapse.types import JsonDict, Requester, UserID, create_requester
-from synapse.util import json_decoder
 from synapse.util.caches.cached_call import RetryOnExceptionCachedCall
 from synapse.util.caches.response_cache import ResponseCache, ResponseCacheContext
+from synapse.util.json import json_decoder
 
 from . import introspection_response_timer
 
diff --git a/synapse/api/auth/msc3861_delegated.py b/synapse/api/auth/msc3861_delegated.py
index c406c683e71..11a89dd3ed6 100644
--- a/synapse/api/auth/msc3861_delegated.py
+++ b/synapse/api/auth/msc3861_delegated.py
@@ -48,9 +48,9 @@
 from synapse.metrics import SERVER_NAME_LABEL
 from synapse.synapse_rust.http_client import HttpClient
 from synapse.types import Requester, UserID, create_requester
-from synapse.util import json_decoder
 from synapse.util.caches.cached_call import RetryOnExceptionCachedCall
 from synapse.util.caches.response_cache import ResponseCache, ResponseCacheContext
+from synapse.util.json import json_decoder
 
 from . import introspection_response_timer
 
diff --git a/synapse/api/errors.py b/synapse/api/errors.py
index ec4d707b7b0..7a643ecfa09 100644
--- a/synapse/api/errors.py
+++ b/synapse/api/errors.py
@@ -30,7 +30,7 @@
 
 from twisted.web import http
 
-from synapse.util import json_decoder
+from synapse.util.json import json_decoder
 
 if typing.TYPE_CHECKING:
     from synapse.config.homeserver import HomeServerConfig
diff --git a/synapse/api/ratelimiting.py b/synapse/api/ratelimiting.py
index 509ef6b2c18..9d1c7801bc3 100644
--- a/synapse/api/ratelimiting.py
+++ b/synapse/api/ratelimiting.py
@@ -26,7 +26,7 @@
 from synapse.config.ratelimiting import RatelimitSettings
 from synapse.storage.databases.main import DataStore
 from synapse.types import Requester
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 if TYPE_CHECKING:
     # To avoid circular imports:
diff --git a/synapse/appservice/scheduler.py b/synapse/appservice/scheduler.py
index 01f77c4cb6d..c8678406a14 100644
--- a/synapse/appservice/scheduler.py
+++ b/synapse/appservice/scheduler.py
@@ -84,7 +84,7 @@
 from synapse.metrics.background_process_metrics import run_as_background_process
 from synapse.storage.databases.main import DataStore
 from synapse.types import DeviceListUpdates, JsonMapping
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
diff --git a/synapse/events/builder.py b/synapse/events/builder.py
index 5e1913d389e..1c9f78c7ca6 100644
--- a/synapse/events/builder.py
+++ b/synapse/events/builder.py
@@ -38,7 +38,7 @@
 from synapse.synapse_rust.events import EventInternalMetadata
 from synapse.types import EventID, JsonDict, StrCollection
 from synapse.types.state import StateFilter
-from synapse.util import Clock
+from synapse.util.clock import Clock
 from synapse.util.stringutils import random_string
 
 if TYPE_CHECKING:
diff --git a/synapse/federation/sender/__init__.py b/synapse/federation/sender/__init__.py
index 6baa2331437..8e3619d1bca 100644
--- a/synapse/federation/sender/__init__.py
+++ b/synapse/federation/sender/__init__.py
@@ -178,7 +178,7 @@
     StrCollection,
     get_domain_from_id,
 )
-from synapse.util import Clock
+from synapse.util.clock import Clock
 from synapse.util.metrics import Measure
 from synapse.util.retryutils import filter_destinations_by_retry_limiter
 
diff --git a/synapse/federation/sender/transaction_manager.py b/synapse/federation/sender/transaction_manager.py
index 050982c4996..b548d9ed70c 100644
--- a/synapse/federation/sender/transaction_manager.py
+++ b/synapse/federation/sender/transaction_manager.py
@@ -36,7 +36,7 @@
 )
 from synapse.metrics import SERVER_NAME_LABEL
 from synapse.types import JsonDict
-from synapse.util import json_decoder
+from synapse.util.json import json_decoder
 from synapse.util.metrics import measure_func
 
 if TYPE_CHECKING:
diff --git a/synapse/handlers/devicemessage.py b/synapse/handlers/devicemessage.py
index b43cbd9c154..860e24d79d3 100644
--- a/synapse/handlers/devicemessage.py
+++ b/synapse/handlers/devicemessage.py
@@ -34,7 +34,7 @@
     set_tag,
 )
 from synapse.types import JsonDict, Requester, StreamKeyType, UserID, get_domain_from_id
-from synapse.util import json_encoder
+from synapse.util.json import json_encoder
 from synapse.util.stringutils import random_string
 
 if TYPE_CHECKING:
diff --git a/synapse/handlers/e2e_keys.py b/synapse/handlers/e2e_keys.py
index b9abad21881..fa3d207a905 100644
--- a/synapse/handlers/e2e_keys.py
+++ b/synapse/handlers/e2e_keys.py
@@ -44,9 +44,9 @@
     get_domain_from_id,
     get_verify_key_from_cross_signing_key,
 )
-from synapse.util import json_decoder
 from synapse.util.async_helpers import Linearizer, concurrently_execute
 from synapse.util.cancellation import cancellable
+from synapse.util.json import json_decoder
 from synapse.util.retryutils import (
     NotRetryingDestination,
     filter_destinations_by_retry_limiter,
diff --git a/synapse/handlers/identity.py b/synapse/handlers/identity.py
index d96b585308b..be757201fc6 100644
--- a/synapse/handlers/identity.py
+++ b/synapse/handlers/identity.py
@@ -39,8 +39,8 @@
 from synapse.http.client import SimpleHttpClient
 from synapse.http.site import SynapseRequest
 from synapse.types import JsonDict, Requester
-from synapse.util import json_decoder
 from synapse.util.hash import sha256_and_url_safe_base64
+from synapse.util.json import json_decoder
 from synapse.util.stringutils import (
     assert_valid_client_secret,
     random_string,
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index d850b617d83..013d521dc3b 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -81,9 +81,10 @@
     create_requester,
 )
 from synapse.types.state import StateFilter
-from synapse.util import json_decoder, json_encoder, log_failure, unwrapFirstError
+from synapse.util import log_failure, unwrapFirstError
 from synapse.util.async_helpers import Linearizer, gather_results
 from synapse.util.caches.expiringcache import ExpiringCache
+from synapse.util.json import json_decoder, json_encoder
 from synapse.util.metrics import measure_func
 from synapse.visibility import get_effective_room_visibility_from_state
 
diff --git a/synapse/handlers/oidc.py b/synapse/handlers/oidc.py
index 8f3e717fb4e..fc93c6b2a8e 100644
--- a/synapse/handlers/oidc.py
+++ b/synapse/handlers/oidc.py
@@ -67,8 +67,9 @@
 from synapse.logging.context import make_deferred_yieldable
 from synapse.module_api import ModuleApi
 from synapse.types import JsonDict, UserID, map_username_to_mxid_localpart
-from synapse.util import Clock, json_decoder
 from synapse.util.caches.cached_call import RetryOnExceptionCachedCall
+from synapse.util.clock import Clock
+from synapse.util.json import json_decoder
 from synapse.util.macaroons import MacaroonGenerator, OidcSessionData
 from synapse.util.templates import _localpart_from_email_filter
 
diff --git a/synapse/handlers/ui_auth/checkers.py b/synapse/handlers/ui_auth/checkers.py
index 32dca8c43ba..f3c295d9f2a 100644
--- a/synapse/handlers/ui_auth/checkers.py
+++ b/synapse/handlers/ui_auth/checkers.py
@@ -27,7 +27,7 @@
 
 from synapse.api.constants import LoginType
 from synapse.api.errors import Codes, LoginError, SynapseError
-from synapse.util import json_decoder
+from synapse.util.json import json_decoder
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
diff --git a/synapse/http/client.py b/synapse/http/client.py
index 1f6d4dcd860..bbb0efe8b52 100644
--- a/synapse/http/client.py
+++ b/synapse/http/client.py
@@ -87,8 +87,8 @@
 from synapse.logging.opentracing import set_tag, start_active_span, tags
 from synapse.metrics import SERVER_NAME_LABEL
 from synapse.types import ISynapseReactor, StrSequence
-from synapse.util import json_decoder
 from synapse.util.async_helpers import timeout_deferred
+from synapse.util.json import json_decoder
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
diff --git a/synapse/http/federation/matrix_federation_agent.py b/synapse/http/federation/matrix_federation_agent.py
index 6ebadf0dbf2..2d152d441e6 100644
--- a/synapse/http/federation/matrix_federation_agent.py
+++ b/synapse/http/federation/matrix_federation_agent.py
@@ -49,7 +49,7 @@
 from synapse.http.proxyagent import ProxyAgent
 from synapse.logging.context import make_deferred_yieldable, run_in_background
 from synapse.types import ISynapseReactor
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 logger = logging.getLogger(__name__)
 
diff --git a/synapse/http/federation/well_known_resolver.py b/synapse/http/federation/well_known_resolver.py
index 70242ad0aef..ac2d0addf79 100644
--- a/synapse/http/federation/well_known_resolver.py
+++ b/synapse/http/federation/well_known_resolver.py
@@ -35,8 +35,9 @@
 
 from synapse.http.client import BodyExceededMaxSize, read_body_with_max_size
 from synapse.logging.context import make_deferred_yieldable
-from synapse.util import Clock, json_decoder
 from synapse.util.caches.ttlcache import TTLCache
+from synapse.util.clock import Clock
+from synapse.util.json import json_decoder
 from synapse.util.metrics import Measure
 
 # period to cache .well-known results for by default
diff --git a/synapse/http/matrixfederationclient.py b/synapse/http/matrixfederationclient.py
index 15f8e147ab6..419e4444abc 100644
--- a/synapse/http/matrixfederationclient.py
+++ b/synapse/http/matrixfederationclient.py
@@ -89,8 +89,8 @@
 from synapse.logging.opentracing import set_tag, start_active_span, tags
 from synapse.metrics import SERVER_NAME_LABEL
 from synapse.types import JsonDict
-from synapse.util import json_decoder
 from synapse.util.async_helpers import AwakenableSleeper, Linearizer, timeout_deferred
+from synapse.util.json import json_decoder
 from synapse.util.metrics import Measure
 from synapse.util.stringutils import parse_and_validate_server_name
 
diff --git a/synapse/http/server.py b/synapse/http/server.py
index e395f79894c..f04c55d4576 100644
--- a/synapse/http/server.py
+++ b/synapse/http/server.py
@@ -77,10 +77,11 @@
 from synapse.config.homeserver import HomeServerConfig
 from synapse.logging.context import defer_to_thread, preserve_fn, run_in_background
 from synapse.logging.opentracing import active_span, start_active_span, trace_servlet
-from synapse.util import Clock, json_encoder
 from synapse.util.caches import intern_dict
 from synapse.util.cancellation import is_function_cancellable
+from synapse.util.clock import Clock
 from synapse.util.iterutils import chunk_seq
+from synapse.util.json import json_encoder
 
 if TYPE_CHECKING:
     import opentracing
diff --git a/synapse/http/servlet.py b/synapse/http/servlet.py
index 69bdce2b834..71e809b3f1c 100644
--- a/synapse/http/servlet.py
+++ b/synapse/http/servlet.py
@@ -51,7 +51,7 @@
 from synapse.http import redact_uri
 from synapse.http.server import HttpServer
 from synapse.types import JsonDict, RoomAlias, RoomID, StrCollection
-from synapse.util import json_decoder
+from synapse.util.json import json_decoder
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
diff --git a/synapse/logging/opentracing.py b/synapse/logging/opentracing.py
index b596b1abdbf..405939d5186 100644
--- a/synapse/logging/opentracing.py
+++ b/synapse/logging/opentracing.py
@@ -204,7 +204,7 @@ def set_fates(clotho, lachesis, atropos, father="Zues", mother="Themis"):
 from twisted.web.http_headers import Headers
 
 from synapse.config import ConfigError
-from synapse.util import json_decoder, json_encoder
+from synapse.util.json import json_decoder, json_encoder
 
 if TYPE_CHECKING:
     from synapse.http.site import SynapseRequest
diff --git a/synapse/media/_base.py b/synapse/media/_base.py
index 29911dab77e..15b28074fd3 100644
--- a/synapse/media/_base.py
+++ b/synapse/media/_base.py
@@ -54,8 +54,8 @@
     make_deferred_yieldable,
     run_in_background,
 )
-from synapse.util import Clock
 from synapse.util.async_helpers import DeferredEvent
+from synapse.util.clock import Clock
 from synapse.util.stringutils import is_ascii
 
 if TYPE_CHECKING:
diff --git a/synapse/media/media_storage.py b/synapse/media/media_storage.py
index afd33c02a12..99d002a8df0 100644
--- a/synapse/media/media_storage.py
+++ b/synapse/media/media_storage.py
@@ -55,7 +55,7 @@
 from synapse.logging.context import defer_to_thread, run_in_background
 from synapse.logging.opentracing import start_active_span, trace, trace_with_opname
 from synapse.media._base import ThreadedFileSender
-from synapse.util import Clock
+from synapse.util.clock import Clock
 from synapse.util.file_consumer import BackgroundFileConsumer
 
 from ..types import JsonDict
diff --git a/synapse/media/oembed.py b/synapse/media/oembed.py
index 16d613d271c..45b481f229b 100644
--- a/synapse/media/oembed.py
+++ b/synapse/media/oembed.py
@@ -27,7 +27,7 @@
 
 from synapse.media.preview_html import parse_html_description
 from synapse.types import JsonDict
-from synapse.util import json_decoder
+from synapse.util.json import json_decoder
 
 if TYPE_CHECKING:
     from lxml import etree
diff --git a/synapse/media/url_previewer.py b/synapse/media/url_previewer.py
index 8f106a3d5f5..81204913f76 100644
--- a/synapse/media/url_previewer.py
+++ b/synapse/media/url_previewer.py
@@ -46,9 +46,9 @@
 from synapse.media.preview_html import decode_body, parse_html_to_open_graph
 from synapse.metrics.background_process_metrics import run_as_background_process
 from synapse.types import JsonDict, UserID
-from synapse.util import json_encoder
 from synapse.util.async_helpers import ObservableDeferred
 from synapse.util.caches.expiringcache import ExpiringCache
+from synapse.util.json import json_encoder
 from synapse.util.stringutils import random_string
 
 if TYPE_CHECKING:
diff --git a/synapse/module_api/__init__.py b/synapse/module_api/__init__.py
index 62181355135..7a419145e0f 100644
--- a/synapse/module_api/__init__.py
+++ b/synapse/module_api/__init__.py
@@ -158,9 +158,9 @@
     create_requester,
 )
 from synapse.types.state import StateFilter
-from synapse.util import Clock
 from synapse.util.async_helpers import maybe_awaitable
 from synapse.util.caches.descriptors import CachedFunction, cached as _cached
+from synapse.util.clock import Clock
 from synapse.util.frozenutils import freeze
 
 if TYPE_CHECKING:
diff --git a/synapse/replication/tcp/commands.py b/synapse/replication/tcp/commands.py
index 6ab53566600..8eec68c3ddc 100644
--- a/synapse/replication/tcp/commands.py
+++ b/synapse/replication/tcp/commands.py
@@ -29,7 +29,7 @@
 from typing import List, Optional, Tuple, Type, TypeVar
 
 from synapse.replication.tcp.streams._base import StreamRow
-from synapse.util import json_decoder, json_encoder
+from synapse.util.json import json_decoder, json_encoder
 
 logger = logging.getLogger(__name__)
 
diff --git a/synapse/replication/tcp/external_cache.py b/synapse/replication/tcp/external_cache.py
index 497b26fcaf9..bcdd55d2e65 100644
--- a/synapse/replication/tcp/external_cache.py
+++ b/synapse/replication/tcp/external_cache.py
@@ -27,7 +27,7 @@
 from synapse.logging import opentracing
 from synapse.logging.context import make_deferred_yieldable
 from synapse.metrics import SERVER_NAME_LABEL
-from synapse.util import json_decoder, json_encoder
+from synapse.util.json import json_decoder, json_encoder
 
 if TYPE_CHECKING:
     from txredisapi import ConnectionHandler
diff --git a/synapse/replication/tcp/protocol.py b/synapse/replication/tcp/protocol.py
index 2ec25bf43da..25a7868cd7b 100644
--- a/synapse/replication/tcp/protocol.py
+++ b/synapse/replication/tcp/protocol.py
@@ -55,7 +55,7 @@
     ServerCommand,
     parse_command_from_line,
 )
-from synapse.util import Clock
+from synapse.util.clock import Clock
 from synapse.util.stringutils import random_string
 
 if TYPE_CHECKING:
diff --git a/synapse/rest/client/sync.py b/synapse/rest/client/sync.py
index c424ca53254..bb63b51599b 100644
--- a/synapse/rest/client/sync.py
+++ b/synapse/rest/client/sync.py
@@ -58,8 +58,8 @@
 from synapse.rest.admin.experimental_features import ExperimentalFeature
 from synapse.types import JsonDict, Requester, SlidingSyncStreamToken, StreamToken
 from synapse.types.rest.client import SlidingSyncBody
-from synapse.util import json_decoder
 from synapse.util.caches.lrucache import LruCache
+from synapse.util.json import json_decoder
 
 from ._base import client_patterns, set_timeline_upper_limit
 
diff --git a/synapse/rest/key/v2/remote_key_resource.py b/synapse/rest/key/v2/remote_key_resource.py
index fea0b9706d7..94c679b9e75 100644
--- a/synapse/rest/key/v2/remote_key_resource.py
+++ b/synapse/rest/key/v2/remote_key_resource.py
@@ -38,8 +38,8 @@
 from synapse.storage.keys import FetchKeyResultForRemote
 from synapse.types import JsonDict
 from synapse.types.rest import RequestBodyModel
-from synapse.util import json_decoder
 from synapse.util.async_helpers import yieldable_gather_results
+from synapse.util.json import json_decoder
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
diff --git a/synapse/rest/well_known.py b/synapse/rest/well_known.py
index e4fe4c45ef4..ae8c6a8fc0d 100644
--- a/synapse/rest/well_known.py
+++ b/synapse/rest/well_known.py
@@ -28,7 +28,7 @@
 from synapse.http.server import DirectServeJsonResource
 from synapse.http.site import SynapseRequest
 from synapse.types import JsonDict
-from synapse.util import json_encoder
+from synapse.util.json import json_encoder
 from synapse.util.stringutils import parse_server_name
 
 if TYPE_CHECKING:
diff --git a/synapse/server.py b/synapse/server.py
index 3fb29a78176..00862eb1376 100644
--- a/synapse/server.py
+++ b/synapse/server.py
@@ -156,7 +156,7 @@
 from synapse.streams.events import EventSources
 from synapse.synapse_rust.rendezvous import RendezvousHandler
 from synapse.types import DomainSpecificString, ISynapseReactor
-from synapse.util import Clock
+from synapse.util.clock import Clock
 from synapse.util.distributor import Distributor
 from synapse.util.macaroons import MacaroonGenerator
 from synapse.util.ratelimitutils import FederationRateLimiter
diff --git a/synapse/storage/_base.py b/synapse/storage/_base.py
index d55c9e18ed6..f214f558978 100644
--- a/synapse/storage/_base.py
+++ b/synapse/storage/_base.py
@@ -29,8 +29,8 @@
     make_in_list_sql_clause,  # noqa: F401
 )
 from synapse.types import get_domain_from_id
-from synapse.util import json_decoder
 from synapse.util.caches.descriptors import CachedFunction
+from synapse.util.json import json_decoder
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
diff --git a/synapse/storage/background_updates.py b/synapse/storage/background_updates.py
index acc0abee63e..9aa9e51aeb6 100644
--- a/synapse/storage/background_updates.py
+++ b/synapse/storage/background_updates.py
@@ -45,7 +45,8 @@
 from synapse.storage.engines import PostgresEngine
 from synapse.storage.types import Connection, Cursor
 from synapse.types import JsonDict, StrCollection
-from synapse.util import Clock, json_encoder
+from synapse.util.clock import Clock
+from synapse.util.json import json_encoder
 
 from . import engines
 
diff --git a/synapse/storage/databases/main/account_data.py b/synapse/storage/databases/main/account_data.py
index c049789e442..16876e5461f 100644
--- a/synapse/storage/databases/main/account_data.py
+++ b/synapse/storage/databases/main/account_data.py
@@ -48,9 +48,9 @@
 from synapse.storage.invite_rule import InviteRulesConfig
 from synapse.storage.util.id_generators import MultiWriterIdGenerator
 from synapse.types import JsonDict, JsonMapping
-from synapse.util import json_encoder
 from synapse.util.caches.descriptors import cached
 from synapse.util.caches.stream_change_cache import StreamChangeCache
+from synapse.util.json import json_encoder
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
diff --git a/synapse/storage/databases/main/appservice.py b/synapse/storage/databases/main/appservice.py
index 9862e574fd1..a676f9be507 100644
--- a/synapse/storage/databases/main/appservice.py
+++ b/synapse/storage/databases/main/appservice.py
@@ -42,8 +42,8 @@
 from synapse.storage.types import Cursor
 from synapse.storage.util.sequence import build_sequence_generator
 from synapse.types import DeviceListUpdates, JsonMapping
-from synapse.util import json_encoder
 from synapse.util.caches.descriptors import _CacheContext, cached
+from synapse.util.json import json_encoder
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
diff --git a/synapse/storage/databases/main/censor_events.py b/synapse/storage/databases/main/censor_events.py
index 5b15fd707d2..3f9f482adda 100644
--- a/synapse/storage/databases/main/censor_events.py
+++ b/synapse/storage/databases/main/censor_events.py
@@ -32,7 +32,7 @@
 )
 from synapse.storage.databases.main.cache import CacheInvalidationWorkerStore
 from synapse.storage.databases.main.events_worker import EventsWorkerStore
-from synapse.util import json_encoder
+from synapse.util.json import json_encoder
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
diff --git a/synapse/storage/databases/main/delayed_events.py b/synapse/storage/databases/main/delayed_events.py
index c88682d55c4..8428ee6ed4d 100644
--- a/synapse/storage/databases/main/delayed_events.py
+++ b/synapse/storage/databases/main/delayed_events.py
@@ -22,7 +22,8 @@
 from synapse.storage.database import LoggingTransaction, StoreError
 from synapse.storage.engines import PostgresEngine
 from synapse.types import JsonDict, RoomID
-from synapse.util import json_encoder, stringutils as stringutils
+from synapse.util import stringutils
+from synapse.util.json import json_encoder
 
 logger = logging.getLogger(__name__)
 
diff --git a/synapse/storage/databases/main/deviceinbox.py b/synapse/storage/databases/main/deviceinbox.py
index c10e2d26113..f6f3c94a0d0 100644
--- a/synapse/storage/databases/main/deviceinbox.py
+++ b/synapse/storage/databases/main/deviceinbox.py
@@ -53,10 +53,11 @@
 )
 from synapse.storage.util.id_generators import MultiWriterIdGenerator
 from synapse.types import JsonDict, StrCollection
-from synapse.util import Duration, json_encoder
+from synapse.util import Duration
 from synapse.util.caches.expiringcache import ExpiringCache
 from synapse.util.caches.stream_change_cache import StreamChangeCache
 from synapse.util.iterutils import batch_iter
+from synapse.util.json import json_encoder
 from synapse.util.stringutils import parse_and_validate_server_name
 
 if TYPE_CHECKING:
diff --git a/synapse/storage/databases/main/devices.py b/synapse/storage/databases/main/devices.py
index a28cc40a958..fc1e1c73f18 100644
--- a/synapse/storage/databases/main/devices.py
+++ b/synapse/storage/databases/main/devices.py
@@ -64,11 +64,11 @@
     StrCollection,
     get_verify_key_from_cross_signing_key,
 )
-from synapse.util import json_decoder, json_encoder
 from synapse.util.caches.descriptors import cached, cachedList
 from synapse.util.caches.stream_change_cache import StreamChangeCache
 from synapse.util.cancellation import cancellable
 from synapse.util.iterutils import batch_iter
+from synapse.util.json import json_decoder, json_encoder
 from synapse.util.stringutils import shortstr
 
 if TYPE_CHECKING:
diff --git a/synapse/storage/databases/main/e2e_room_keys.py b/synapse/storage/databases/main/e2e_room_keys.py
index 904ae5cb58e..d978e115e42 100644
--- a/synapse/storage/databases/main/e2e_room_keys.py
+++ b/synapse/storage/databases/main/e2e_room_keys.py
@@ -41,7 +41,7 @@
     LoggingTransaction,
 )
 from synapse.types import JsonDict, JsonSerializable, StreamKeyType
-from synapse.util import json_encoder
+from synapse.util.json import json_encoder
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
diff --git a/synapse/storage/databases/main/end_to_end_keys.py b/synapse/storage/databases/main/end_to_end_keys.py
index 17ccefe6b5b..cc389d15826 100644
--- a/synapse/storage/databases/main/end_to_end_keys.py
+++ b/synapse/storage/databases/main/end_to_end_keys.py
@@ -61,10 +61,10 @@
 from synapse.storage.engines import PostgresEngine
 from synapse.storage.util.id_generators import MultiWriterIdGenerator
 from synapse.types import JsonDict, JsonMapping, MultiWriterStreamToken
-from synapse.util import json_decoder, json_encoder
 from synapse.util.caches.descriptors import cached, cachedList
 from synapse.util.cancellation import cancellable
 from synapse.util.iterutils import batch_iter
+from synapse.util.json import json_decoder, json_encoder
 
 if TYPE_CHECKING:
     from synapse.handlers.e2e_keys import SignatureListItem
diff --git a/synapse/storage/databases/main/event_federation.py b/synapse/storage/databases/main/event_federation.py
index 26a91109dfe..5c9bd2e848d 100644
--- a/synapse/storage/databases/main/event_federation.py
+++ b/synapse/storage/databases/main/event_federation.py
@@ -59,11 +59,11 @@
 from synapse.storage.databases.main.signatures import SignatureWorkerStore
 from synapse.storage.engines import PostgresEngine, Sqlite3Engine
 from synapse.types import JsonDict, StrCollection
-from synapse.util import json_encoder
 from synapse.util.caches.descriptors import cached
 from synapse.util.caches.lrucache import LruCache
 from synapse.util.cancellation import cancellable
 from synapse.util.iterutils import batch_iter
+from synapse.util.json import json_encoder
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
diff --git a/synapse/storage/databases/main/event_push_actions.py b/synapse/storage/databases/main/event_push_actions.py
index f42023418e2..4db0230421f 100644
--- a/synapse/storage/databases/main/event_push_actions.py
+++ b/synapse/storage/databases/main/event_push_actions.py
@@ -107,8 +107,8 @@
 from synapse.storage.databases.main.receipts import ReceiptsWorkerStore
 from synapse.storage.databases.main.stream import StreamWorkerStore
 from synapse.types import JsonDict, StrCollection
-from synapse.util import json_encoder
 from synapse.util.caches.descriptors import cached
+from synapse.util.json import json_encoder
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
diff --git a/synapse/storage/databases/main/events.py b/synapse/storage/databases/main/events.py
index a50e889b9df..b6037468b39 100644
--- a/synapse/storage/databases/main/events.py
+++ b/synapse/storage/databases/main/events.py
@@ -83,9 +83,9 @@
 )
 from synapse.types.handlers import SLIDING_SYNC_DEFAULT_BUMP_EVENT_TYPES
 from synapse.types.state import StateFilter
-from synapse.util import json_encoder
 from synapse.util.events import get_plain_text_topic_from_event_content
 from synapse.util.iterutils import batch_iter, sorted_topologically
+from synapse.util.json import json_encoder
 from synapse.util.stringutils import non_null_str_or_none
 
 if TYPE_CHECKING:
diff --git a/synapse/storage/databases/main/events_bg_updates.py b/synapse/storage/databases/main/events_bg_updates.py
index 8a59091da0f..0a0102ee64b 100644
--- a/synapse/storage/databases/main/events_bg_updates.py
+++ b/synapse/storage/databases/main/events_bg_updates.py
@@ -58,8 +58,8 @@
 from synapse.types.handlers import SLIDING_SYNC_DEFAULT_BUMP_EVENT_TYPES
 from synapse.types.state import StateFilter
 from synapse.types.storage import _BackgroundUpdates
-from synapse.util import json_encoder
 from synapse.util.iterutils import batch_iter
+from synapse.util.json import json_encoder
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
diff --git a/synapse/storage/databases/main/lock.py b/synapse/storage/databases/main/lock.py
index e733f65cb1e..27c3578a316 100644
--- a/synapse/storage/databases/main/lock.py
+++ b/synapse/storage/databases/main/lock.py
@@ -38,7 +38,7 @@
     LoggingTransaction,
 )
 from synapse.types import ISynapseReactor
-from synapse.util import Clock
+from synapse.util.clock import Clock
 from synapse.util.stringutils import random_string
 
 if TYPE_CHECKING:
diff --git a/synapse/storage/databases/main/push_rule.py b/synapse/storage/databases/main/push_rule.py
index d6861405569..1860be17131 100644
--- a/synapse/storage/databases/main/push_rule.py
+++ b/synapse/storage/databases/main/push_rule.py
@@ -56,10 +56,11 @@
 from synapse.storage.util.id_generators import IdGenerator, MultiWriterIdGenerator
 from synapse.synapse_rust.push import FilteredPushRules, PushRule, PushRules
 from synapse.types import JsonDict
-from synapse.util import json_encoder, unwrapFirstError
+from synapse.util import unwrapFirstError
 from synapse.util.async_helpers import gather_results
 from synapse.util.caches.descriptors import cached, cachedList
 from synapse.util.caches.stream_change_cache import StreamChangeCache
+from synapse.util.json import json_encoder
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
diff --git a/synapse/storage/databases/main/pusher.py b/synapse/storage/databases/main/pusher.py
index 9a0a12b5c10..1b2aa79ab17 100644
--- a/synapse/storage/databases/main/pusher.py
+++ b/synapse/storage/databases/main/pusher.py
@@ -42,8 +42,8 @@
 )
 from synapse.storage.util.id_generators import MultiWriterIdGenerator
 from synapse.types import JsonDict
-from synapse.util import json_encoder
 from synapse.util.caches.descriptors import cached
+from synapse.util.json import json_encoder
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
diff --git a/synapse/storage/databases/main/receipts.py b/synapse/storage/databases/main/receipts.py
index d74bb0184a1..ff4eb9acb29 100644
--- a/synapse/storage/databases/main/receipts.py
+++ b/synapse/storage/databases/main/receipts.py
@@ -55,10 +55,10 @@
     PersistedPosition,
     StrCollection,
 )
-from synapse.util import json_encoder
 from synapse.util.caches.descriptors import cached, cachedList
 from synapse.util.caches.stream_change_cache import StreamChangeCache
 from synapse.util.iterutils import batch_iter
+from synapse.util.json import json_encoder
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
diff --git a/synapse/storage/databases/main/room.py b/synapse/storage/databases/main/room.py
index 6ffc3aed34b..9f03c084a59 100644
--- a/synapse/storage/databases/main/room.py
+++ b/synapse/storage/databases/main/room.py
@@ -65,8 +65,8 @@
 from synapse.storage.types import Cursor
 from synapse.storage.util.id_generators import IdGenerator, MultiWriterIdGenerator
 from synapse.types import JsonDict, RetentionPolicy, StrCollection, ThirdPartyInstanceID
-from synapse.util import json_encoder
 from synapse.util.caches.descriptors import cached, cachedList
+from synapse.util.json import json_encoder
 from synapse.util.stringutils import MXC_REGEX
 
 if TYPE_CHECKING:
diff --git a/synapse/storage/databases/main/session.py b/synapse/storage/databases/main/session.py
index 8a1331d4c8e..8a5fa8386cd 100644
--- a/synapse/storage/databases/main/session.py
+++ b/synapse/storage/databases/main/session.py
@@ -30,7 +30,7 @@
     LoggingTransaction,
 )
 from synapse.types import JsonDict
-from synapse.util import json_encoder
+from synapse.util.json import json_encoder
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
diff --git a/synapse/storage/databases/main/sliding_sync.py b/synapse/storage/databases/main/sliding_sync.py
index 72ec8e6b909..f7af3e88d3f 100644
--- a/synapse/storage/databases/main/sliding_sync.py
+++ b/synapse/storage/databases/main/sliding_sync.py
@@ -35,8 +35,8 @@
     RoomStatusMap,
     RoomSyncConfig,
 )
-from synapse.util import json_encoder
 from synapse.util.caches.descriptors import cached
+from synapse.util.json import json_encoder
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
diff --git a/synapse/storage/databases/main/tags.py b/synapse/storage/databases/main/tags.py
index 97b190bccc3..94cf7f40525 100644
--- a/synapse/storage/databases/main/tags.py
+++ b/synapse/storage/databases/main/tags.py
@@ -30,8 +30,8 @@
 from synapse.storage.databases.main.account_data import AccountDataWorkerStore
 from synapse.storage.util.id_generators import AbstractStreamIdGenerator
 from synapse.types import JsonDict, JsonMapping
-from synapse.util import json_encoder
 from synapse.util.caches.descriptors import cached
+from synapse.util.json import json_encoder
 
 logger = logging.getLogger(__name__)
 
diff --git a/synapse/storage/databases/main/task_scheduler.py b/synapse/storage/databases/main/task_scheduler.py
index 4956870b1af..2d4804fef6f 100644
--- a/synapse/storage/databases/main/task_scheduler.py
+++ b/synapse/storage/databases/main/task_scheduler.py
@@ -29,7 +29,7 @@
     make_in_list_sql_clause,
 )
 from synapse.types import JsonDict, JsonMapping, ScheduledTask, TaskStatus
-from synapse.util import json_encoder
+from synapse.util.json import json_encoder
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
diff --git a/synapse/storage/databases/main/ui_auth.py b/synapse/storage/databases/main/ui_auth.py
index 17bd0ac09ab..569925e39fa 100644
--- a/synapse/storage/databases/main/ui_auth.py
+++ b/synapse/storage/databases/main/ui_auth.py
@@ -27,7 +27,8 @@
 from synapse.storage._base import SQLBaseStore, db_to_json
 from synapse.storage.database import LoggingTransaction
 from synapse.types import JsonDict
-from synapse.util import json_encoder, stringutils
+from synapse.util import stringutils
+from synapse.util.json import json_encoder
 
 
 @attr.s(slots=True, auto_attribs=True)
diff --git a/synapse/util/async_helpers.py b/synapse/util/async_helpers.py
index c21b7887f9e..51bb1bf165d 100644
--- a/synapse/util/async_helpers.py
+++ b/synapse/util/async_helpers.py
@@ -65,7 +65,7 @@
     run_coroutine_in_background,
     run_in_background,
 )
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 logger = logging.getLogger(__name__)
 
diff --git a/synapse/util/batching_queue.py b/synapse/util/batching_queue.py
index 4c0f129423b..4c4037412aa 100644
--- a/synapse/util/batching_queue.py
+++ b/synapse/util/batching_queue.py
@@ -39,7 +39,7 @@
 from synapse.logging.context import PreserveLoggingContext, make_deferred_yieldable
 from synapse.metrics import SERVER_NAME_LABEL
 from synapse.metrics.background_process_metrics import run_as_background_process
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 logger = logging.getLogger(__name__)
 
diff --git a/synapse/util/caches/expiringcache.py b/synapse/util/caches/expiringcache.py
index 1962a3fdfa4..305af5051c4 100644
--- a/synapse/util/caches/expiringcache.py
+++ b/synapse/util/caches/expiringcache.py
@@ -29,8 +29,8 @@
 
 from synapse.config import cache as cache_config
 from synapse.metrics.background_process_metrics import run_as_background_process
-from synapse.util import Clock
 from synapse.util.caches import EvictionReason, register_cache
+from synapse.util.clock import Clock
 
 logger = logging.getLogger(__name__)
 
diff --git a/synapse/util/caches/lrucache.py b/synapse/util/caches/lrucache.py
index 927162700a9..d1a338ab99d 100644
--- a/synapse/util/caches/lrucache.py
+++ b/synapse/util/caches/lrucache.py
@@ -53,13 +53,14 @@
     run_as_background_process,
 )
 from synapse.metrics.jemalloc import get_jemalloc_stats
-from synapse.util import Clock, caches
+from synapse.util import caches
 from synapse.util.caches import CacheMetric, EvictionReason, register_cache
 from synapse.util.caches.treecache import (
     TreeCache,
     iterate_tree_cache_entry,
     iterate_tree_cache_items,
 )
+from synapse.util.clock import Clock
 from synapse.util.linked_list import ListNode
 
 if TYPE_CHECKING:
diff --git a/synapse/util/caches/response_cache.py b/synapse/util/caches/response_cache.py
index 49a9151916e..79e34262df5 100644
--- a/synapse/util/caches/response_cache.py
+++ b/synapse/util/caches/response_cache.py
@@ -41,9 +41,9 @@
     start_active_span,
     start_active_span_follows_from,
 )
-from synapse.util import Clock
 from synapse.util.async_helpers import AbstractObservableDeferred, ObservableDeferred
 from synapse.util.caches import EvictionReason, register_cache
+from synapse.util.clock import Clock
 
 logger = logging.getLogger(__name__)
 
diff --git a/synapse/util/macaroons.py b/synapse/util/macaroons.py
index 6fa15543ec7..d683a57ab1d 100644
--- a/synapse/util/macaroons.py
+++ b/synapse/util/macaroons.py
@@ -28,7 +28,8 @@
 import pymacaroons
 from pymacaroons.exceptions import MacaroonVerificationFailedException
 
-from synapse.util import Clock, stringutils
+from synapse.util import stringutils
+from synapse.util.clock import Clock
 
 MacaroonType = Literal["access", "delete_pusher", "session"]
 
diff --git a/synapse/util/metrics.py b/synapse/util/metrics.py
index 608a4d48489..09ccdb8ca30 100644
--- a/synapse/util/metrics.py
+++ b/synapse/util/metrics.py
@@ -42,7 +42,7 @@
     current_context,
 )
 from synapse.metrics import SERVER_NAME_LABEL, InFlightGauge
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 logger = logging.getLogger(__name__)
 
diff --git a/synapse/util/ratelimitutils.py b/synapse/util/ratelimitutils.py
index 88edc071611..695eb462bfe 100644
--- a/synapse/util/ratelimitutils.py
+++ b/synapse/util/ratelimitutils.py
@@ -53,7 +53,7 @@
 )
 from synapse.logging.opentracing import start_active_span
 from synapse.metrics import SERVER_NAME_LABEL, Histogram, LaterGauge
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 if typing.TYPE_CHECKING:
     from contextlib import _GeneratorContextManager
diff --git a/synapse/util/retryutils.py b/synapse/util/retryutils.py
index 149df405b34..42a0cc7aa81 100644
--- a/synapse/util/retryutils.py
+++ b/synapse/util/retryutils.py
@@ -27,7 +27,7 @@
 from synapse.metrics.background_process_metrics import run_as_background_process
 from synapse.storage import DataStore
 from synapse.types import StrCollection
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 if TYPE_CHECKING:
     from synapse.notifier import Notifier
diff --git a/synapse/visibility.py b/synapse/visibility.py
index d460d8f4c20..662f2636d01 100644
--- a/synapse/visibility.py
+++ b/synapse/visibility.py
@@ -55,7 +55,7 @@
     get_domain_from_id,
 )
 from synapse.types.state import StateFilter
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 logger = logging.getLogger(__name__)
 filtered_event_logger = logging.getLogger("synapse.visibility.filtered_event_debug")
diff --git a/synmark/suites/logging.py b/synmark/suites/logging.py
index 32282ba6cbf..03bf5a94a7c 100644
--- a/synmark/suites/logging.py
+++ b/synmark/suites/logging.py
@@ -37,7 +37,7 @@
 from synapse.logging import RemoteHandler
 from synapse.synapse_rust import reset_logging_config
 from synapse.types import ISynapseReactor
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 
 class LineCounter(LineOnlyReceiver):
diff --git a/tests/api/test_auth.py b/tests/api/test_auth.py
index b8fb21ab0d6..2f6a76970c8 100644
--- a/tests/api/test_auth.py
+++ b/tests/api/test_auth.py
@@ -39,7 +39,7 @@
 from synapse.server import HomeServer
 from synapse.storage.databases.main.registration import TokenLookupResult
 from synapse.types import Requester, UserID
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.unittest import override_config
diff --git a/tests/api/test_filtering.py b/tests/api/test_filtering.py
index 8ad9a5a6f7a..d74878a4e13 100644
--- a/tests/api/test_filtering.py
+++ b/tests/api/test_filtering.py
@@ -33,7 +33,7 @@
 from synapse.api.presence import UserPresenceState
 from synapse.server import HomeServer
 from synapse.types import JsonDict, UserID
-from synapse.util import Clock
+from synapse.util.clock import Clock
 from synapse.util.frozenutils import freeze
 
 from tests import unittest
diff --git a/tests/api/test_urls.py b/tests/api/test_urls.py
index bb46008ad28..00f54237ab3 100644
--- a/tests/api/test_urls.py
+++ b/tests/api/test_urls.py
@@ -17,7 +17,7 @@
 
 from synapse.api.urls import LoginSSORedirectURIBuilder
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase
 
diff --git a/tests/app/test_openid_listener.py b/tests/app/test_openid_listener.py
index 63cb5ff46f5..6ca514d557f 100644
--- a/tests/app/test_openid_listener.py
+++ b/tests/app/test_openid_listener.py
@@ -29,7 +29,7 @@
 from synapse.config.server import parse_listener_def
 from synapse.server import HomeServer
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.server import make_request
 from tests.unittest import HomeserverTestCase
diff --git a/tests/app/test_phone_stats_home.py b/tests/app/test_phone_stats_home.py
index 93af614defe..73c3a9fd981 100644
--- a/tests/app/test_phone_stats_home.py
+++ b/tests/app/test_phone_stats_home.py
@@ -2,7 +2,7 @@
 from synapse.app.phone_stats_home import start_phone_stats_home
 from synapse.rest.client import login, room
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.server import ThreadedMemoryReactorClock
 from tests.unittest import HomeserverTestCase
diff --git a/tests/appservice/test_api.py b/tests/appservice/test_api.py
index 5eba6d20c8b..085dfd2d1df 100644
--- a/tests/appservice/test_api.py
+++ b/tests/appservice/test_api.py
@@ -26,7 +26,7 @@
 from synapse.appservice import ApplicationService
 from synapse.server import HomeServer
 from synapse.types import JsonDict, UserID
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.unittest import override_config
diff --git a/tests/appservice/test_scheduler.py b/tests/appservice/test_scheduler.py
index 11319bc52d2..9498ea12790 100644
--- a/tests/appservice/test_scheduler.py
+++ b/tests/appservice/test_scheduler.py
@@ -41,7 +41,7 @@
 from synapse.logging.context import make_deferred_yieldable
 from synapse.server import HomeServer
 from synapse.types import DeviceListUpdates, JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/config/test_room_directory.py b/tests/config/test_room_directory.py
index 5f3d8be2a56..4e044245e22 100644
--- a/tests/config/test_room_directory.py
+++ b/tests/config/test_room_directory.py
@@ -27,7 +27,7 @@
 from synapse.config._base import RootConfig
 from synapse.config.room_directory import RoomDirectoryConfig
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.unittest import override_config
diff --git a/tests/crypto/test_keyring.py b/tests/crypto/test_keyring.py
index 80f9bd097e5..1dc0de73fd9 100644
--- a/tests/crypto/test_keyring.py
+++ b/tests/crypto/test_keyring.py
@@ -49,7 +49,7 @@
 from synapse.server import HomeServer
 from synapse.storage.keys import FetchKeyResult
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.unittest import logcontext_clean, override_config
diff --git a/tests/events/test_auto_accept_invites.py b/tests/events/test_auto_accept_invites.py
index 8f1dc869847..fa7ea641057 100644
--- a/tests/events/test_auto_accept_invites.py
+++ b/tests/events/test_auto_accept_invites.py
@@ -41,7 +41,7 @@
 from synapse.rest.client import login, room
 from synapse.server import HomeServer
 from synapse.types import StreamToken, UserID, UserInfo, create_requester
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.handlers.test_sync import generate_sync_config
 from tests.unittest import (
diff --git a/tests/events/test_presence_router.py b/tests/events/test_presence_router.py
index f7d55223b1d..696d9dd6e27 100644
--- a/tests/events/test_presence_router.py
+++ b/tests/events/test_presence_router.py
@@ -34,7 +34,7 @@
 from synapse.rest.client import login, presence, room
 from synapse.server import HomeServer
 from synapse.types import JsonDict, StreamToken, create_requester
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.handlers.test_sync import SyncRequestKey, generate_sync_config
 from tests.unittest import (
diff --git a/tests/events/test_snapshot.py b/tests/events/test_snapshot.py
index 6d24730ed70..4d1dca08eff 100644
--- a/tests/events/test_snapshot.py
+++ b/tests/events/test_snapshot.py
@@ -26,7 +26,7 @@
 from synapse.rest import admin
 from synapse.rest.client import login, room
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.test_utils.event_injection import create_event
diff --git a/tests/federation/test_federation_catch_up.py b/tests/federation/test_federation_catch_up.py
index f99911b1025..5edb6517671 100644
--- a/tests/federation/test_federation_catch_up.py
+++ b/tests/federation/test_federation_catch_up.py
@@ -16,7 +16,7 @@
 from synapse.rest.client import login, room
 from synapse.server import HomeServer
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 from synapse.util.retryutils import NotRetryingDestination
 
 from tests.test_utils import event_injection
diff --git a/tests/federation/test_federation_client.py b/tests/federation/test_federation_client.py
index df688cd21f4..0535aed1073 100644
--- a/tests/federation/test_federation_client.py
+++ b/tests/federation/test_federation_client.py
@@ -30,7 +30,7 @@
 from synapse.rest import admin
 from synapse.rest.client import login, room
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.test_utils import FakeResponse, event_injection
 from tests.unittest import FederatingHomeserverTestCase
diff --git a/tests/federation/test_federation_devices.py b/tests/federation/test_federation_devices.py
index bf6204a7e30..c935669ce2e 100644
--- a/tests/federation/test_federation_devices.py
+++ b/tests/federation/test_federation_devices.py
@@ -26,7 +26,7 @@
 from synapse.handlers.device import DeviceListUpdater
 from synapse.server import HomeServer
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 from synapse.util.retryutils import NotRetryingDestination
 
 from tests import unittest
diff --git a/tests/federation/test_federation_media.py b/tests/federation/test_federation_media.py
index b9ec2794a3b..1e849fa605c 100644
--- a/tests/federation/test_federation_media.py
+++ b/tests/federation/test_federation_media.py
@@ -32,7 +32,7 @@
 )
 from synapse.server import HomeServer
 from synapse.types import UserID
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.media.test_media_storage import small_png
diff --git a/tests/federation/test_federation_out_of_band_membership.py b/tests/federation/test_federation_out_of_band_membership.py
index acf343930f9..fa4e7c63ba6 100644
--- a/tests/federation/test_federation_out_of_band_membership.py
+++ b/tests/federation/test_federation_out_of_band_membership.py
@@ -50,7 +50,7 @@
 from synapse.types.handlers.sliding_sync import (
     StateValues,
 )
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.utils import test_timeout
diff --git a/tests/federation/test_federation_sender.py b/tests/federation/test_federation_sender.py
index b8dd61d04f7..27b69a91805 100644
--- a/tests/federation/test_federation_sender.py
+++ b/tests/federation/test_federation_sender.py
@@ -36,7 +36,7 @@
 from synapse.server import HomeServer
 from synapse.storage.databases.main.events_worker import EventMetadata
 from synapse.types import JsonDict, ReadReceipt
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase
 
diff --git a/tests/federation/test_federation_server.py b/tests/federation/test_federation_server.py
index 52fd32ba850..262f94367c0 100644
--- a/tests/federation/test_federation_server.py
+++ b/tests/federation/test_federation_server.py
@@ -40,7 +40,7 @@
 from synapse.server import HomeServer
 from synapse.storage.controllers.state import server_acl_evaluator_from_event
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.unittest import override_config
diff --git a/tests/federation/transport/test_knocking.py b/tests/federation/transport/test_knocking.py
index 14345be0f3d..a2439382559 100644
--- a/tests/federation/transport/test_knocking.py
+++ b/tests/federation/transport/test_knocking.py
@@ -31,7 +31,7 @@
 from synapse.rest.client import login, room
 from synapse.server import HomeServer
 from synapse.types import RoomAlias
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.test_utils import event_injection
 from tests.unittest import FederatingHomeserverTestCase, HomeserverTestCase
diff --git a/tests/handlers/test_admin.py b/tests/handlers/test_admin.py
index 906d241f1a4..49bd3ba3f4c 100644
--- a/tests/handlers/test_admin.py
+++ b/tests/handlers/test_admin.py
@@ -31,7 +31,7 @@
 from synapse.rest.client import knock, login, room
 from synapse.server import HomeServer
 from synapse.types import UserID
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/handlers/test_appservice.py b/tests/handlers/test_appservice.py
index a47b03b143b..999d7f5e6cd 100644
--- a/tests/handlers/test_appservice.py
+++ b/tests/handlers/test_appservice.py
@@ -45,7 +45,7 @@
     StreamKeyType,
     UserID,
 )
-from synapse.util import Clock
+from synapse.util.clock import Clock
 from synapse.util.stringutils import random_string
 
 from tests import unittest
diff --git a/tests/handlers/test_auth.py b/tests/handlers/test_auth.py
index 0d9940c63eb..acefd707f5a 100644
--- a/tests/handlers/test_auth.py
+++ b/tests/handlers/test_auth.py
@@ -29,7 +29,7 @@
 from synapse.rest import admin
 from synapse.rest.client import login
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/handlers/test_cas.py b/tests/handlers/test_cas.py
index 9de5e678634..f677f3be2a6 100644
--- a/tests/handlers/test_cas.py
+++ b/tests/handlers/test_cas.py
@@ -25,7 +25,7 @@
 
 from synapse.handlers.cas import CasResponse
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase, override_config
 
diff --git a/tests/handlers/test_deactivate_account.py b/tests/handlers/test_deactivate_account.py
index b7b83877806..1b749cee1f8 100644
--- a/tests/handlers/test_deactivate_account.py
+++ b/tests/handlers/test_deactivate_account.py
@@ -28,7 +28,7 @@
 from synapse.server import HomeServer
 from synapse.synapse_rust.push import PushRule
 from synapse.types import UserID, create_requester
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase
 
diff --git a/tests/handlers/test_device.py b/tests/handlers/test_device.py
index 195cdfeaefd..5b04da8640b 100644
--- a/tests/handlers/test_device.py
+++ b/tests/handlers/test_device.py
@@ -35,7 +35,7 @@
 from synapse.server import HomeServer
 from synapse.storage.databases.main.appservice import _make_exclusive_regex
 from synapse.types import JsonDict, UserID, create_requester
-from synapse.util import Clock
+from synapse.util.clock import Clock
 from synapse.util.task_scheduler import TaskScheduler
 
 from tests import unittest
diff --git a/tests/handlers/test_directory.py b/tests/handlers/test_directory.py
index 4d6243ef748..45b8f2353a5 100644
--- a/tests/handlers/test_directory.py
+++ b/tests/handlers/test_directory.py
@@ -31,7 +31,7 @@
 from synapse.rest.client import directory, login, room
 from synapse.server import HomeServer
 from synapse.types import JsonDict, RoomAlias, create_requester
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/handlers/test_e2e_keys.py b/tests/handlers/test_e2e_keys.py
index fda485d413f..4f0b1574b35 100644
--- a/tests/handlers/test_e2e_keys.py
+++ b/tests/handlers/test_e2e_keys.py
@@ -35,7 +35,7 @@
 from synapse.server import HomeServer
 from synapse.storage.databases.main.appservice import _make_exclusive_regex
 from synapse.types import JsonDict, UserID
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.unittest import override_config
diff --git a/tests/handlers/test_e2e_room_keys.py b/tests/handlers/test_e2e_room_keys.py
index 9b280659ab6..910c24c1672 100644
--- a/tests/handlers/test_e2e_room_keys.py
+++ b/tests/handlers/test_e2e_room_keys.py
@@ -27,7 +27,7 @@
 
 from synapse.api.errors import SynapseError
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/handlers/test_federation.py b/tests/handlers/test_federation.py
index 4de90e6578e..a88ed6207c3 100644
--- a/tests/handlers/test_federation.py
+++ b/tests/handlers/test_federation.py
@@ -43,7 +43,7 @@
 from synapse.rest.client import login, room
 from synapse.server import HomeServer
 from synapse.storage.databases.main.events_worker import EventCacheEntry
-from synapse.util import Clock
+from synapse.util.clock import Clock
 from synapse.util.events import generate_fake_event_id
 
 from tests import unittest
diff --git a/tests/handlers/test_federation_event.py b/tests/handlers/test_federation_event.py
index 02dd60e76d2..3b3f12796e0 100644
--- a/tests/handlers/test_federation_event.py
+++ b/tests/handlers/test_federation_event.py
@@ -39,7 +39,7 @@
 from synapse.state import StateResolutionStore
 from synapse.state.v2 import _mainline_sort, _reverse_topological_power_sort
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.test_utils import event_injection
diff --git a/tests/handlers/test_message.py b/tests/handlers/test_message.py
index 0a1092eae4b..4262e805e78 100644
--- a/tests/handlers/test_message.py
+++ b/tests/handlers/test_message.py
@@ -31,7 +31,7 @@
 from synapse.rest.client import login, room
 from synapse.server import HomeServer
 from synapse.types import create_requester
-from synapse.util import Clock
+from synapse.util.clock import Clock
 from synapse.util.stringutils import random_string
 
 from tests import unittest
diff --git a/tests/handlers/test_oauth_delegation.py b/tests/handlers/test_oauth_delegation.py
index d24614f6a35..1e3206b23ae 100644
--- a/tests/handlers/test_oauth_delegation.py
+++ b/tests/handlers/test_oauth_delegation.py
@@ -54,7 +54,7 @@
 from synapse.rest.client import account, devices, keys, login, logout, register
 from synapse.server import HomeServer
 from synapse.types import JsonDict, UserID, create_requester
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.server import FakeChannel
 from tests.test_utils import get_awaitable_result
diff --git a/tests/handlers/test_oidc.py b/tests/handlers/test_oidc.py
index db37e7d1858..5207382f00f 100644
--- a/tests/handlers/test_oidc.py
+++ b/tests/handlers/test_oidc.py
@@ -31,7 +31,7 @@
 from synapse.http.site import SynapseRequest
 from synapse.server import HomeServer
 from synapse.types import JsonDict, UserID
-from synapse.util import Clock
+from synapse.util.clock import Clock
 from synapse.util.macaroons import get_value_from_macaroon
 from synapse.util.stringutils import random_string
 
diff --git a/tests/handlers/test_password_providers.py b/tests/handlers/test_password_providers.py
index 0a78fe0304a..aa418750638 100644
--- a/tests/handlers/test_password_providers.py
+++ b/tests/handlers/test_password_providers.py
@@ -35,7 +35,7 @@
 from synapse.rest.client import account, devices, login, logout, register
 from synapse.server import HomeServer
 from synapse.types import JsonDict, UserID
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.server import FakeChannel
diff --git a/tests/handlers/test_presence.py b/tests/handlers/test_presence.py
index 51b6c60531d..de1bc90c678 100644
--- a/tests/handlers/test_presence.py
+++ b/tests/handlers/test_presence.py
@@ -57,7 +57,7 @@
 from synapse.storage.database import LoggingDatabaseConnection
 from synapse.storage.keys import FetchKeyResult
 from synapse.types import JsonDict, UserID, get_domain_from_id
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.replication._base import BaseMultiWorkerStreamTestCase
diff --git a/tests/handlers/test_profile.py b/tests/handlers/test_profile.py
index 93934e9ff7f..73426c7b04b 100644
--- a/tests/handlers/test_profile.py
+++ b/tests/handlers/test_profile.py
@@ -30,7 +30,7 @@
 from synapse.rest import admin
 from synapse.server import HomeServer
 from synapse.types import JsonDict, UserID
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/handlers/test_receipts.py b/tests/handlers/test_receipts.py
index cf04ac6e002..4febccbfcf2 100644
--- a/tests/handlers/test_receipts.py
+++ b/tests/handlers/test_receipts.py
@@ -27,7 +27,7 @@
 from synapse.api.constants import EduTypes, ReceiptTypes
 from synapse.server import HomeServer
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/handlers/test_register.py b/tests/handlers/test_register.py
index 43ded2fc10b..5e2eb8dee74 100644
--- a/tests/handlers/test_register.py
+++ b/tests/handlers/test_register.py
@@ -43,7 +43,7 @@
     UserID,
     create_requester,
 )
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import override_config
 from tests.utils import mock_getRawHeaders
diff --git a/tests/handlers/test_room_member.py b/tests/handlers/test_room_member.py
index 3084f180f50..92c7c36602b 100644
--- a/tests/handlers/test_room_member.py
+++ b/tests/handlers/test_room_member.py
@@ -15,7 +15,7 @@
 from synapse.federation.federation_client import SendJoinResult
 from synapse.server import HomeServer
 from synapse.types import UserID, create_requester
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.replication._base import BaseMultiWorkerStreamTestCase
 from tests.server import make_request
diff --git a/tests/handlers/test_room_policy.py b/tests/handlers/test_room_policy.py
index 3ea6f13cce4..d1d0c484fa6 100644
--- a/tests/handlers/test_room_policy.py
+++ b/tests/handlers/test_room_policy.py
@@ -23,7 +23,7 @@
 from synapse.server import HomeServer
 from synapse.types import JsonDict, UserID
 from synapse.types.handlers.policy_server import RECOMMENDATION_OK, RECOMMENDATION_SPAM
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.test_utils import event_injection
diff --git a/tests/handlers/test_room_summary.py b/tests/handlers/test_room_summary.py
index 27646d7365e..00592b9871a 100644
--- a/tests/handlers/test_room_summary.py
+++ b/tests/handlers/test_room_summary.py
@@ -42,7 +42,7 @@
 from synapse.rest.client import login, room
 from synapse.server import HomeServer
 from synapse.types import JsonDict, UserID, create_requester
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.unittest import override_config
diff --git a/tests/handlers/test_saml.py b/tests/handlers/test_saml.py
index 98a4276a3a4..f7cbf911139 100644
--- a/tests/handlers/test_saml.py
+++ b/tests/handlers/test_saml.py
@@ -30,7 +30,7 @@
 from synapse.module_api import ModuleApi
 from synapse.server import HomeServer
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase, override_config
 
diff --git a/tests/handlers/test_sliding_sync.py b/tests/handlers/test_sliding_sync.py
index 8c390f0c57f..1ffd15cadbd 100644
--- a/tests/handlers/test_sliding_sync.py
+++ b/tests/handlers/test_sliding_sync.py
@@ -46,7 +46,7 @@
 from synapse.types import JsonDict, StateMap, StreamToken, UserID, create_requester
 from synapse.types.handlers.sliding_sync import PerConnectionState, SlidingSyncConfig
 from synapse.types.state import StateFilter
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.replication._base import BaseMultiWorkerStreamTestCase
diff --git a/tests/handlers/test_sso.py b/tests/handlers/test_sso.py
index 896e4fac9a0..b09d0a42f52 100644
--- a/tests/handlers/test_sso.py
+++ b/tests/handlers/test_sso.py
@@ -27,7 +27,7 @@
 from synapse.api.errors import Codes, SynapseError
 from synapse.http.client import RawHeaders
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.test_utils import SMALL_PNG, FakeResponse
diff --git a/tests/handlers/test_stats.py b/tests/handlers/test_stats.py
index cd17cd86e06..abec5c2e392 100644
--- a/tests/handlers/test_stats.py
+++ b/tests/handlers/test_stats.py
@@ -26,7 +26,7 @@
 from synapse.rest.client import login, room
 from synapse.server import HomeServer
 from synapse.storage.databases.main import stats
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/handlers/test_sync.py b/tests/handlers/test_sync.py
index 9d3e88c126d..c61788fe900 100644
--- a/tests/handlers/test_sync.py
+++ b/tests/handlers/test_sync.py
@@ -50,7 +50,7 @@
     UserID,
     create_requester,
 )
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 import tests.unittest
 import tests.utils
diff --git a/tests/handlers/test_typing.py b/tests/handlers/test_typing.py
index 614b12c62aa..4d2807151ef 100644
--- a/tests/handlers/test_typing.py
+++ b/tests/handlers/test_typing.py
@@ -36,7 +36,7 @@
 from synapse.http.federation.matrix_federation_agent import MatrixFederationAgent
 from synapse.server import HomeServer
 from synapse.types import JsonDict, Requester, StreamKeyType, UserID, create_requester
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.server import ThreadedMemoryReactorClock
diff --git a/tests/handlers/test_user_directory.py b/tests/handlers/test_user_directory.py
index 7458fe0885e..1ba0be51a2c 100644
--- a/tests/handlers/test_user_directory.py
+++ b/tests/handlers/test_user_directory.py
@@ -32,7 +32,7 @@
 from synapse.server import HomeServer
 from synapse.storage.roommember import ProfileInfo
 from synapse.types import JsonDict, UserID, UserProfile, create_requester
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.storage.test_user_directory import GetUserDirectoryTables
diff --git a/tests/handlers/test_worker_lock.py b/tests/handlers/test_worker_lock.py
index 3d3904eac7c..61ff51ff923 100644
--- a/tests/handlers/test_worker_lock.py
+++ b/tests/handlers/test_worker_lock.py
@@ -26,7 +26,7 @@
 from twisted.internet.testing import MemoryReactor
 
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.replication._base import BaseMultiWorkerStreamTestCase
diff --git a/tests/http/test_matrixfederationclient.py b/tests/http/test_matrixfederationclient.py
index 224883b635d..44752d69cbf 100644
--- a/tests/http/test_matrixfederationclient.py
+++ b/tests/http/test_matrixfederationclient.py
@@ -48,7 +48,7 @@
     current_context,
 )
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.replication._base import BaseMultiWorkerStreamTestCase
 from tests.server import FakeTransport
diff --git a/tests/http/test_simple_client.py b/tests/http/test_simple_client.py
index c5ead599880..25c0e1081b3 100644
--- a/tests/http/test_simple_client.py
+++ b/tests/http/test_simple_client.py
@@ -29,7 +29,7 @@
 from synapse.http import RequestTimedOutError
 from synapse.http.client import SimpleHttpClient
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase
 
diff --git a/tests/http/test_site.py b/tests/http/test_site.py
index 2eca4587e7d..9e6d929c9ef 100644
--- a/tests/http/test_site.py
+++ b/tests/http/test_site.py
@@ -24,7 +24,7 @@
 
 from synapse.app.homeserver import SynapseHomeServer
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase
 
diff --git a/tests/logging/test_opentracing.py b/tests/logging/test_opentracing.py
index 5fe57d100ec..951102701cb 100644
--- a/tests/logging/test_opentracing.py
+++ b/tests/logging/test_opentracing.py
@@ -35,7 +35,7 @@
     tag_args,
     trace_with_opname,
 )
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 try:
     import opentracing
diff --git a/tests/media/test_media_retention.py b/tests/media/test_media_retention.py
index 6e01b9aecb5..aec1adb0407 100644
--- a/tests/media/test_media_retention.py
+++ b/tests/media/test_media_retention.py
@@ -30,7 +30,7 @@
 from synapse.rest.client import login, register, room
 from synapse.server import HomeServer
 from synapse.types import UserID
-from synapse.util import Clock
+from synapse.util.clock import Clock
 from synapse.util.stringutils import (
     random_string,
 )
diff --git a/tests/media/test_media_storage.py b/tests/media/test_media_storage.py
index bf334c03717..28c4ce676a8 100644
--- a/tests/media/test_media_storage.py
+++ b/tests/media/test_media_storage.py
@@ -56,7 +56,7 @@
 from synapse.rest.client import login, media
 from synapse.server import HomeServer
 from synapse.types import JsonDict, RoomAlias
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.server import FakeChannel
diff --git a/tests/media/test_oembed.py b/tests/media/test_oembed.py
index afae7e048cf..dc13c03df33 100644
--- a/tests/media/test_oembed.py
+++ b/tests/media/test_oembed.py
@@ -29,7 +29,7 @@
 from synapse.media.oembed import OEmbedProvider, OEmbedResult
 from synapse.server import HomeServer
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase
 
diff --git a/tests/media/test_url_previewer.py b/tests/media/test_url_previewer.py
index bd7190e3e9f..3d706c7e90d 100644
--- a/tests/media/test_url_previewer.py
+++ b/tests/media/test_url_previewer.py
@@ -23,7 +23,7 @@
 from twisted.internet.testing import MemoryReactor
 
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.unittest import override_config
diff --git a/tests/metrics/test_phone_home_stats.py b/tests/metrics/test_phone_home_stats.py
index cf18d8635d0..4462385dae0 100644
--- a/tests/metrics/test_phone_home_stats.py
+++ b/tests/metrics/test_phone_home_stats.py
@@ -23,7 +23,7 @@
 from synapse.rest import admin, login, register, room
 from synapse.server import HomeServer
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.server import ThreadedMemoryReactorClock
diff --git a/tests/module_api/test_account_data_manager.py b/tests/module_api/test_account_data_manager.py
index 6539871c11a..0397c6a786a 100644
--- a/tests/module_api/test_account_data_manager.py
+++ b/tests/module_api/test_account_data_manager.py
@@ -23,7 +23,7 @@
 from synapse.api.errors import SynapseError
 from synapse.rest import admin
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase
 
diff --git a/tests/module_api/test_api.py b/tests/module_api/test_api.py
index 6b761de36d1..86f987f2927 100644
--- a/tests/module_api/test_api.py
+++ b/tests/module_api/test_api.py
@@ -36,7 +36,7 @@
 from synapse.rest.client import login, notifications, presence, profile, room
 from synapse.server import HomeServer
 from synapse.types import JsonDict, UserID, create_requester
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.events.test_presence_router import send_presence_update, sync_presence
 from tests.replication._base import BaseMultiWorkerStreamTestCase
diff --git a/tests/module_api/test_event_unsigned_addition.py b/tests/module_api/test_event_unsigned_addition.py
index 52e3858e6fe..b6b43c469f3 100644
--- a/tests/module_api/test_event_unsigned_addition.py
+++ b/tests/module_api/test_event_unsigned_addition.py
@@ -24,7 +24,7 @@
 from synapse.rest import admin, login, room
 from synapse.server import HomeServer
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase
 
diff --git a/tests/module_api/test_spamchecker.py b/tests/module_api/test_spamchecker.py
index fa19232ee9b..3f4d1d9d5f0 100644
--- a/tests/module_api/test_spamchecker.py
+++ b/tests/module_api/test_spamchecker.py
@@ -20,7 +20,7 @@
 from synapse.rest import admin, login, room, room_upgrade_rest_servlet
 from synapse.server import HomeServer
 from synapse.types import Codes, JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.server import FakeChannel
 from tests.unittest import HomeserverTestCase
diff --git a/tests/push/test_bulk_push_rule_evaluator.py b/tests/push/test_bulk_push_rule_evaluator.py
index 7342a72dff1..560d7234ec5 100644
--- a/tests/push/test_bulk_push_rule_evaluator.py
+++ b/tests/push/test_bulk_push_rule_evaluator.py
@@ -34,7 +34,7 @@
 from synapse.rest.client import login, push_rule, register, room
 from synapse.server import HomeServer
 from synapse.types import JsonDict, create_requester
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase, override_config
 
diff --git a/tests/push/test_email.py b/tests/push/test_email.py
index 4d9e42ac2cc..80a22044ddc 100644
--- a/tests/push/test_email.py
+++ b/tests/push/test_email.py
@@ -35,7 +35,7 @@
 from synapse.rest.client import login, room
 from synapse.rest.synapse.client.unsubscribe import UnsubscribeResource
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.server import FakeSite, make_request
 from tests.unittest import HomeserverTestCase
diff --git a/tests/push/test_http.py b/tests/push/test_http.py
index 370233c7308..4c8aae5782a 100644
--- a/tests/push/test_http.py
+++ b/tests/push/test_http.py
@@ -32,7 +32,7 @@
 from synapse.rest.client import login, push_rule, pusher, receipts, room, versions
 from synapse.server import HomeServer
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase, override_config
 
diff --git a/tests/push/test_push_rule_evaluator.py b/tests/push/test_push_rule_evaluator.py
index 3a351acffa5..718c9614e50 100644
--- a/tests/push/test_push_rule_evaluator.py
+++ b/tests/push/test_push_rule_evaluator.py
@@ -36,7 +36,7 @@
 from synapse.storage.databases.main.appservice import _make_exclusive_regex
 from synapse.synapse_rust.push import PushRuleEvaluator
 from synapse.types import JsonDict, JsonMapping, UserID
-from synapse.util import Clock
+from synapse.util.clock import Clock
 from synapse.util.frozenutils import freeze
 
 from tests import unittest
diff --git a/tests/replication/_base.py b/tests/replication/_base.py
index e756021937d..36d32139088 100644
--- a/tests/replication/_base.py
+++ b/tests/replication/_base.py
@@ -38,7 +38,7 @@
 )
 from synapse.replication.tcp.resource import ReplicationStreamProtocolFactory
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.server import FakeTransport
diff --git a/tests/replication/storage/_base.py b/tests/replication/storage/_base.py
index 97e744127c5..fb99cb23354 100644
--- a/tests/replication/storage/_base.py
+++ b/tests/replication/storage/_base.py
@@ -25,7 +25,7 @@
 from twisted.internet.testing import MemoryReactor
 
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.replication._base import BaseStreamTestCase
 
diff --git a/tests/replication/storage/test_events.py b/tests/replication/storage/test_events.py
index b3ca2049954..fce32690052 100644
--- a/tests/replication/storage/test_events.py
+++ b/tests/replication/storage/test_events.py
@@ -38,7 +38,7 @@
 from synapse.storage.databases.main.events_worker import EventsWorkerStore
 from synapse.storage.roommember import RoomsForUser
 from synapse.types import PersistedEventPosition
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from ._base import BaseWorkerStoreTestCase
 
diff --git a/tests/replication/tcp/streams/test_events.py b/tests/replication/tcp/streams/test_events.py
index cd6fe53a964..782dad39f5c 100644
--- a/tests/replication/tcp/streams/test_events.py
+++ b/tests/replication/tcp/streams/test_events.py
@@ -38,7 +38,7 @@
 from synapse.rest import admin
 from synapse.rest.client import login, room
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.replication._base import BaseStreamTestCase
 from tests.test_utils.event_injection import inject_event, inject_member_event
diff --git a/tests/replication/tcp/streams/test_thread_subscriptions.py b/tests/replication/tcp/streams/test_thread_subscriptions.py
index 7283aa851e2..04e46b9d93d 100644
--- a/tests/replication/tcp/streams/test_thread_subscriptions.py
+++ b/tests/replication/tcp/streams/test_thread_subscriptions.py
@@ -20,7 +20,7 @@
 )
 from synapse.server import HomeServer
 from synapse.storage.database import LoggingTransaction
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.replication._base import BaseStreamTestCase
 
diff --git a/tests/replication/test_auth.py b/tests/replication/test_auth.py
index 640ed4e8f31..30f636b3f13 100644
--- a/tests/replication/test_auth.py
+++ b/tests/replication/test_auth.py
@@ -24,7 +24,7 @@
 
 from synapse.rest.client import register
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.replication._base import BaseMultiWorkerStreamTestCase
 from tests.server import FakeChannel, make_request
diff --git a/tests/replication/test_federation_ack.py b/tests/replication/test_federation_ack.py
index 440c1d45afc..e6b9ea53832 100644
--- a/tests/replication/test_federation_ack.py
+++ b/tests/replication/test_federation_ack.py
@@ -28,7 +28,7 @@
 from synapse.replication.tcp.protocol import IReplicationConnection
 from synapse.replication.tcp.streams.federation import FederationStream
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase
 
diff --git a/tests/replication/test_federation_sender_shard.py b/tests/replication/test_federation_sender_shard.py
index 1fed4ec631d..92259f2542a 100644
--- a/tests/replication/test_federation_sender_shard.py
+++ b/tests/replication/test_federation_sender_shard.py
@@ -41,7 +41,7 @@
 from synapse.server import HomeServer
 from synapse.storage.keys import FetchKeyResult
 from synapse.types import JsonDict, UserID, create_requester
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.replication._base import BaseMultiWorkerStreamTestCase
 from tests.server import get_clock
diff --git a/tests/replication/test_multi_media_repo.py b/tests/replication/test_multi_media_repo.py
index 228a803c1d7..f712ad1fe37 100644
--- a/tests/replication/test_multi_media_repo.py
+++ b/tests/replication/test_multi_media_repo.py
@@ -30,7 +30,7 @@
 from synapse.rest import admin
 from synapse.rest.client import login, media
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.http import (
     TestServerTLSConnectionFactory,
diff --git a/tests/replication/test_pusher_shard.py b/tests/replication/test_pusher_shard.py
index d63054c631a..033711b9b88 100644
--- a/tests/replication/test_pusher_shard.py
+++ b/tests/replication/test_pusher_shard.py
@@ -27,7 +27,7 @@
 from synapse.rest import admin
 from synapse.rest.client import login, room
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.replication._base import BaseMultiWorkerStreamTestCase
 
diff --git a/tests/replication/test_sharded_event_persister.py b/tests/replication/test_sharded_event_persister.py
index 797ad003ef6..f37394c1f5c 100644
--- a/tests/replication/test_sharded_event_persister.py
+++ b/tests/replication/test_sharded_event_persister.py
@@ -27,7 +27,7 @@
 from synapse.rest.client import login, room, sync
 from synapse.server import HomeServer
 from synapse.storage.util.id_generators import MultiWriterIdGenerator
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.replication._base import BaseMultiWorkerStreamTestCase
 from tests.server import make_request
diff --git a/tests/replication/test_sharded_receipts.py b/tests/replication/test_sharded_receipts.py
index 6b3ecdad782..b986f335428 100644
--- a/tests/replication/test_sharded_receipts.py
+++ b/tests/replication/test_sharded_receipts.py
@@ -28,7 +28,7 @@
 from synapse.server import HomeServer
 from synapse.storage.util.id_generators import MultiWriterIdGenerator
 from synapse.types import StreamToken
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.replication._base import BaseMultiWorkerStreamTestCase
 from tests.server import make_request
diff --git a/tests/rest/admin/test_admin.py b/tests/rest/admin/test_admin.py
index b74e8388e9d..2a17389feb3 100644
--- a/tests/rest/admin/test_admin.py
+++ b/tests/rest/admin/test_admin.py
@@ -33,7 +33,7 @@
 from synapse.rest.client import login, media, room
 from synapse.server import HomeServer
 from synapse.types import UserID
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.test_utils import SMALL_PNG
diff --git a/tests/rest/admin/test_background_updates.py b/tests/rest/admin/test_background_updates.py
index dd116e79f1f..25112baaa2b 100644
--- a/tests/rest/admin/test_background_updates.py
+++ b/tests/rest/admin/test_background_updates.py
@@ -30,7 +30,7 @@
 from synapse.server import HomeServer
 from synapse.storage.background_updates import BackgroundUpdater
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/rest/admin/test_device.py b/tests/rest/admin/test_device.py
index c564e0c9a73..4dff59e1806 100644
--- a/tests/rest/admin/test_device.py
+++ b/tests/rest/admin/test_device.py
@@ -29,7 +29,7 @@
 from synapse.handlers.device import DeviceWriterHandler
 from synapse.rest.client import devices, login
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/rest/admin/test_event_reports.py b/tests/rest/admin/test_event_reports.py
index a6f958658fe..28be7fcd97a 100644
--- a/tests/rest/admin/test_event_reports.py
+++ b/tests/rest/admin/test_event_reports.py
@@ -27,7 +27,7 @@
 from synapse.rest.client import login, reporting, room
 from synapse.server import HomeServer
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/rest/admin/test_federation.py b/tests/rest/admin/test_federation.py
index cfea480bf0a..d0b57d1faa1 100644
--- a/tests/rest/admin/test_federation.py
+++ b/tests/rest/admin/test_federation.py
@@ -29,7 +29,7 @@
 from synapse.rest.client import login, room
 from synapse.server import HomeServer
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/rest/admin/test_media.py b/tests/rest/admin/test_media.py
index f863b5f8e72..3bf9f67e091 100644
--- a/tests/rest/admin/test_media.py
+++ b/tests/rest/admin/test_media.py
@@ -32,7 +32,7 @@
 from synapse.media.filepath import MediaFilePaths
 from synapse.rest.client import login, profile, room
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.test_utils import SMALL_CMYK_JPEG, SMALL_PNG
diff --git a/tests/rest/admin/test_registration_tokens.py b/tests/rest/admin/test_registration_tokens.py
index b8e111c804b..9afe86b7240 100644
--- a/tests/rest/admin/test_registration_tokens.py
+++ b/tests/rest/admin/test_registration_tokens.py
@@ -28,7 +28,7 @@
 from synapse.api.errors import Codes
 from synapse.rest.client import login
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/rest/admin/test_room.py b/tests/rest/admin/test_room.py
index ee5d0419ab9..30b2de26e4a 100644
--- a/tests/rest/admin/test_room.py
+++ b/tests/rest/admin/test_room.py
@@ -45,7 +45,7 @@
     purge_room_tables_with_room_id_column,
 )
 from synapse.types import UserID
-from synapse.util import Clock
+from synapse.util.clock import Clock
 from synapse.util.task_scheduler import TaskScheduler
 
 from tests import unittest
diff --git a/tests/rest/admin/test_scheduled_tasks.py b/tests/rest/admin/test_scheduled_tasks.py
index ea7afc0101f..16b80e214b5 100644
--- a/tests/rest/admin/test_scheduled_tasks.py
+++ b/tests/rest/admin/test_scheduled_tasks.py
@@ -22,7 +22,7 @@
 from synapse.rest.client import login
 from synapse.server import HomeServer
 from synapse.types import JsonMapping, ScheduledTask, TaskStatus
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/rest/admin/test_server_notice.py b/tests/rest/admin/test_server_notice.py
index 1f77e31d481..ebb6867d7c5 100644
--- a/tests/rest/admin/test_server_notice.py
+++ b/tests/rest/admin/test_server_notice.py
@@ -28,7 +28,7 @@
 from synapse.server import HomeServer
 from synapse.storage.roommember import RoomsForUser
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 from synapse.util.stringutils import random_string
 
 from tests import unittest
diff --git a/tests/rest/admin/test_statistics.py b/tests/rest/admin/test_statistics.py
index 10efc4ef8b2..4026c47a23e 100644
--- a/tests/rest/admin/test_statistics.py
+++ b/tests/rest/admin/test_statistics.py
@@ -29,7 +29,7 @@
 from synapse.rest.client import login
 from synapse.server import HomeServer
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.test_utils import SMALL_PNG
diff --git a/tests/rest/admin/test_user.py b/tests/rest/admin/test_user.py
index 4432b6a7a08..ca41cd6c31f 100644
--- a/tests/rest/admin/test_user.py
+++ b/tests/rest/admin/test_user.py
@@ -61,7 +61,7 @@
 from synapse.server import HomeServer
 from synapse.storage.databases.main.client_ips import LAST_SEEN_GRANULARITY
 from synapse.types import JsonDict, UserID, create_requester
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.replication._base import BaseMultiWorkerStreamTestCase
diff --git a/tests/rest/admin/test_username_available.py b/tests/rest/admin/test_username_available.py
index 9c3ab3e64cd..b2c1d7ac0ab 100644
--- a/tests/rest/admin/test_username_available.py
+++ b/tests/rest/admin/test_username_available.py
@@ -26,7 +26,7 @@
 from synapse.api.errors import Codes, SynapseError
 from synapse.rest.client import login
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/rest/client/sliding_sync/test_connection_tracking.py b/tests/rest/client/sliding_sync/test_connection_tracking.py
index f8ce1104a87..16d13fcc860 100644
--- a/tests/rest/client/sliding_sync/test_connection_tracking.py
+++ b/tests/rest/client/sliding_sync/test_connection_tracking.py
@@ -21,7 +21,7 @@
 from synapse.api.constants import EventTypes
 from synapse.rest.client import login, room, sync
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.rest.client.sliding_sync.test_sliding_sync import SlidingSyncBase
 
diff --git a/tests/rest/client/sliding_sync/test_extension_account_data.py b/tests/rest/client/sliding_sync/test_extension_account_data.py
index 59490657220..8e08b4a2ac6 100644
--- a/tests/rest/client/sliding_sync/test_extension_account_data.py
+++ b/tests/rest/client/sliding_sync/test_extension_account_data.py
@@ -24,7 +24,7 @@
 from synapse.rest.client import login, room, sendtodevice, sync
 from synapse.server import HomeServer
 from synapse.types import StreamKeyType
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.rest.client.sliding_sync.test_sliding_sync import SlidingSyncBase
 from tests.server import TimedOutException
diff --git a/tests/rest/client/sliding_sync/test_extension_e2ee.py b/tests/rest/client/sliding_sync/test_extension_e2ee.py
index baf6a5882e0..4a5e4070382 100644
--- a/tests/rest/client/sliding_sync/test_extension_e2ee.py
+++ b/tests/rest/client/sliding_sync/test_extension_e2ee.py
@@ -21,7 +21,7 @@
 from synapse.rest.client import devices, login, room, sync
 from synapse.server import HomeServer
 from synapse.types import JsonDict, StreamKeyType
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.rest.client.sliding_sync.test_sliding_sync import SlidingSyncBase
 from tests.server import TimedOutException
diff --git a/tests/rest/client/sliding_sync/test_extension_receipts.py b/tests/rest/client/sliding_sync/test_extension_receipts.py
index 1bba3038dbc..8c02217cde6 100644
--- a/tests/rest/client/sliding_sync/test_extension_receipts.py
+++ b/tests/rest/client/sliding_sync/test_extension_receipts.py
@@ -22,7 +22,7 @@
 from synapse.rest.client import login, receipts, room, sync
 from synapse.server import HomeServer
 from synapse.types import StreamKeyType
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.rest.client.sliding_sync.test_sliding_sync import SlidingSyncBase
 from tests.server import TimedOutException
diff --git a/tests/rest/client/sliding_sync/test_extension_thread_subscriptions.py b/tests/rest/client/sliding_sync/test_extension_thread_subscriptions.py
index 775c4f96c91..4e151b9aae6 100644
--- a/tests/rest/client/sliding_sync/test_extension_thread_subscriptions.py
+++ b/tests/rest/client/sliding_sync/test_extension_thread_subscriptions.py
@@ -21,7 +21,7 @@
 from synapse.rest.client import login, room, sync, thread_subscriptions
 from synapse.server import HomeServer
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.rest.client.sliding_sync.test_sliding_sync import SlidingSyncBase
 
diff --git a/tests/rest/client/sliding_sync/test_extension_to_device.py b/tests/rest/client/sliding_sync/test_extension_to_device.py
index 151a5be665b..a77b0a2e9f9 100644
--- a/tests/rest/client/sliding_sync/test_extension_to_device.py
+++ b/tests/rest/client/sliding_sync/test_extension_to_device.py
@@ -22,7 +22,7 @@
 from synapse.rest.client import login, sendtodevice, sync
 from synapse.server import HomeServer
 from synapse.types import JsonDict, StreamKeyType
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.rest.client.sliding_sync.test_sliding_sync import SlidingSyncBase
 from tests.server import TimedOutException
diff --git a/tests/rest/client/sliding_sync/test_extension_typing.py b/tests/rest/client/sliding_sync/test_extension_typing.py
index 37c90d6ec28..68b935aaf92 100644
--- a/tests/rest/client/sliding_sync/test_extension_typing.py
+++ b/tests/rest/client/sliding_sync/test_extension_typing.py
@@ -22,7 +22,7 @@
 from synapse.rest.client import login, room, sync
 from synapse.server import HomeServer
 from synapse.types import StreamKeyType
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.rest.client.sliding_sync.test_sliding_sync import SlidingSyncBase
 from tests.server import TimedOutException
diff --git a/tests/rest/client/sliding_sync/test_extensions.py b/tests/rest/client/sliding_sync/test_extensions.py
index 0643596e59c..1c167b0414e 100644
--- a/tests/rest/client/sliding_sync/test_extensions.py
+++ b/tests/rest/client/sliding_sync/test_extensions.py
@@ -23,7 +23,7 @@
 from synapse.api.constants import ReceiptTypes
 from synapse.rest.client import login, receipts, room, sync
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.rest.client.sliding_sync.test_sliding_sync import SlidingSyncBase
 
diff --git a/tests/rest/client/sliding_sync/test_lists_filters.py b/tests/rest/client/sliding_sync/test_lists_filters.py
index 57d00a2a7af..3b7b2a16d81 100644
--- a/tests/rest/client/sliding_sync/test_lists_filters.py
+++ b/tests/rest/client/sliding_sync/test_lists_filters.py
@@ -28,7 +28,7 @@
 from synapse.rest.client import login, room, sync, tags
 from synapse.server import HomeServer
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.rest.client.sliding_sync.test_sliding_sync import SlidingSyncBase
 
diff --git a/tests/rest/client/sliding_sync/test_room_subscriptions.py b/tests/rest/client/sliding_sync/test_room_subscriptions.py
index b78e4f20451..811478f1ba7 100644
--- a/tests/rest/client/sliding_sync/test_room_subscriptions.py
+++ b/tests/rest/client/sliding_sync/test_room_subscriptions.py
@@ -22,7 +22,7 @@
 from synapse.api.constants import EventTypes, HistoryVisibility
 from synapse.rest.client import login, room, sync
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.rest.client.sliding_sync.test_sliding_sync import SlidingSyncBase
 
diff --git a/tests/rest/client/sliding_sync/test_rooms_invites.py b/tests/rest/client/sliding_sync/test_rooms_invites.py
index a0f4ccd2cc7..5a463303dd0 100644
--- a/tests/rest/client/sliding_sync/test_rooms_invites.py
+++ b/tests/rest/client/sliding_sync/test_rooms_invites.py
@@ -22,7 +22,7 @@
 from synapse.rest.client import login, room, sync
 from synapse.server import HomeServer
 from synapse.types import UserID
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.rest.client.sliding_sync.test_sliding_sync import SlidingSyncBase
 
diff --git a/tests/rest/client/sliding_sync/test_rooms_meta.py b/tests/rest/client/sliding_sync/test_rooms_meta.py
index 4559bc76465..9e3f8aaf943 100644
--- a/tests/rest/client/sliding_sync/test_rooms_meta.py
+++ b/tests/rest/client/sliding_sync/test_rooms_meta.py
@@ -22,7 +22,7 @@
 from synapse.api.room_versions import RoomVersions
 from synapse.rest.client import login, room, sync
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.rest.client.sliding_sync.test_sliding_sync import SlidingSyncBase
 from tests.test_utils.event_injection import create_event
diff --git a/tests/rest/client/sliding_sync/test_rooms_required_state.py b/tests/rest/client/sliding_sync/test_rooms_required_state.py
index cfff167c6ec..210280bc488 100644
--- a/tests/rest/client/sliding_sync/test_rooms_required_state.py
+++ b/tests/rest/client/sliding_sync/test_rooms_required_state.py
@@ -23,7 +23,7 @@
 from synapse.handlers.sliding_sync import StateValues
 from synapse.rest.client import knock, login, room, sync
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.rest.client.sliding_sync.test_sliding_sync import SlidingSyncBase
 from tests.test_utils.event_injection import mark_event_as_partial_state
diff --git a/tests/rest/client/sliding_sync/test_rooms_timeline.py b/tests/rest/client/sliding_sync/test_rooms_timeline.py
index 3d950eb20b9..44a6068c11c 100644
--- a/tests/rest/client/sliding_sync/test_rooms_timeline.py
+++ b/tests/rest/client/sliding_sync/test_rooms_timeline.py
@@ -23,7 +23,7 @@
 from synapse.rest.client import login, room, sync
 from synapse.server import HomeServer
 from synapse.types import StrSequence
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.rest.client.sliding_sync.test_sliding_sync import SlidingSyncBase
 
diff --git a/tests/rest/client/sliding_sync/test_sliding_sync.py b/tests/rest/client/sliding_sync/test_sliding_sync.py
index ea4ee16359f..8da5863b3ad 100644
--- a/tests/rest/client/sliding_sync/test_sliding_sync.py
+++ b/tests/rest/client/sliding_sync/test_sliding_sync.py
@@ -42,7 +42,7 @@
     StreamKeyType,
     StreamToken,
 )
-from synapse.util import Clock
+from synapse.util.clock import Clock
 from synapse.util.stringutils import random_string
 
 from tests import unittest
diff --git a/tests/rest/client/test_account.py b/tests/rest/client/test_account.py
index 9a3202bd934..773f49dfc94 100644
--- a/tests/rest/client/test_account.py
+++ b/tests/rest/client/test_account.py
@@ -39,7 +39,7 @@
 from synapse.server import HomeServer
 from synapse.storage._base import db_to_json
 from synapse.types import JsonDict, UserID
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.server import FakeSite, make_request
diff --git a/tests/rest/client/test_auth.py b/tests/rest/client/test_auth.py
index 4fe506845c4..f5b7f957210 100644
--- a/tests/rest/client/test_auth.py
+++ b/tests/rest/client/test_auth.py
@@ -35,7 +35,7 @@
 from synapse.server import HomeServer
 from synapse.storage.database import LoggingTransaction
 from synapse.types import JsonDict, UserID
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.handlers.test_oidc import HAS_OIDC
diff --git a/tests/rest/client/test_capabilities.py b/tests/rest/client/test_capabilities.py
index 8ae1cc935a2..0eec3130618 100644
--- a/tests/rest/client/test_capabilities.py
+++ b/tests/rest/client/test_capabilities.py
@@ -25,7 +25,7 @@
 from synapse.api.room_versions import KNOWN_ROOM_VERSIONS
 from synapse.rest.client import capabilities, login
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.unittest import override_config
diff --git a/tests/rest/client/test_consent.py b/tests/rest/client/test_consent.py
index 1a64b3984fb..d127f3abd21 100644
--- a/tests/rest/client/test_consent.py
+++ b/tests/rest/client/test_consent.py
@@ -28,7 +28,7 @@
 from synapse.rest.client import login, room
 from synapse.rest.consent import consent_resource
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.server import FakeSite, make_request
diff --git a/tests/rest/client/test_delayed_events.py b/tests/rest/client/test_delayed_events.py
index 4b338d333fe..221a4902f20 100644
--- a/tests/rest/client/test_delayed_events.py
+++ b/tests/rest/client/test_delayed_events.py
@@ -26,7 +26,7 @@
 from synapse.rest.client import delayed_events, login, room, versions
 from synapse.server import HomeServer
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.unittest import HomeserverTestCase
diff --git a/tests/rest/client/test_devices.py b/tests/rest/client/test_devices.py
index 2c498e97e15..acb5a956e99 100644
--- a/tests/rest/client/test_devices.py
+++ b/tests/rest/client/test_devices.py
@@ -29,7 +29,7 @@
 from synapse.rest.client import keys, login, register
 from synapse.server import HomeServer
 from synapse.types import JsonDict, UserID, create_requester
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/rest/client/test_directory.py b/tests/rest/client/test_directory.py
index 6548ac6fa8a..f67f495dd2d 100644
--- a/tests/rest/client/test_directory.py
+++ b/tests/rest/client/test_directory.py
@@ -26,7 +26,7 @@
 from synapse.rest.client import directory, login, room
 from synapse.server import HomeServer
 from synapse.types import RoomAlias, UserID
-from synapse.util import Clock
+from synapse.util.clock import Clock
 from synapse.util.stringutils import random_string
 
 from tests import unittest
diff --git a/tests/rest/client/test_ephemeral_message.py b/tests/rest/client/test_ephemeral_message.py
index 5b5c2208251..6d806c630d8 100644
--- a/tests/rest/client/test_ephemeral_message.py
+++ b/tests/rest/client/test_ephemeral_message.py
@@ -26,7 +26,7 @@
 from synapse.rest.client import room
 from synapse.server import HomeServer
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/rest/client/test_events.py b/tests/rest/client/test_events.py
index 142509bbf7f..65371f4c7e9 100644
--- a/tests/rest/client/test_events.py
+++ b/tests/rest/client/test_events.py
@@ -29,7 +29,7 @@
 from synapse.api.constants import EduTypes
 from synapse.rest.client import events, login, room
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/rest/client/test_filter.py b/tests/rest/client/test_filter.py
index 4153fb322d7..0897c67ac3f 100644
--- a/tests/rest/client/test_filter.py
+++ b/tests/rest/client/test_filter.py
@@ -25,7 +25,7 @@
 from synapse.rest.client import filter
 from synapse.server import HomeServer
 from synapse.types import UserID
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/rest/client/test_identity.py b/tests/rest/client/test_identity.py
index 87af18f4735..cc29d0c01d6 100644
--- a/tests/rest/client/test_identity.py
+++ b/tests/rest/client/test_identity.py
@@ -25,7 +25,7 @@
 import synapse.rest.admin
 from synapse.rest.client import login, room
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/rest/client/test_login.py b/tests/rest/client/test_login.py
index 8f9856fa2e4..3376d134c49 100644
--- a/tests/rest/client/test_login.py
+++ b/tests/rest/client/test_login.py
@@ -52,7 +52,7 @@
 from synapse.rest.synapse.client import build_synapse_client_resource_tree
 from synapse.server import HomeServer
 from synapse.types import JsonDict, UserID, create_requester
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.handlers.test_oidc import HAS_OIDC
diff --git a/tests/rest/client/test_login_token_request.py b/tests/rest/client/test_login_token_request.py
index 202d2cf3512..835336f3d9d 100644
--- a/tests/rest/client/test_login_token_request.py
+++ b/tests/rest/client/test_login_token_request.py
@@ -24,7 +24,7 @@
 from synapse.rest import admin
 from synapse.rest.client import login, login_token_request, versions
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.unittest import override_config
diff --git a/tests/rest/client/test_media.py b/tests/rest/client/test_media.py
index ec6760feea0..91bf94b672d 100644
--- a/tests/rest/client/test_media.py
+++ b/tests/rest/client/test_media.py
@@ -59,7 +59,7 @@
 from synapse.rest.client import login, media
 from synapse.server import HomeServer
 from synapse.types import JsonDict, UserID
-from synapse.util import Clock
+from synapse.util.clock import Clock
 from synapse.util.stringutils import parse_and_validate_mxc_uri
 
 from tests import unittest
diff --git a/tests/rest/client/test_mutual_rooms.py b/tests/rest/client/test_mutual_rooms.py
index 2e372846808..8580d090064 100644
--- a/tests/rest/client/test_mutual_rooms.py
+++ b/tests/rest/client/test_mutual_rooms.py
@@ -25,7 +25,7 @@
 import synapse.rest.admin
 from synapse.rest.client import login, mutual_rooms, room
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.server import FakeChannel
diff --git a/tests/rest/client/test_notifications.py b/tests/rest/client/test_notifications.py
index ec66567817d..e00152389bb 100644
--- a/tests/rest/client/test_notifications.py
+++ b/tests/rest/client/test_notifications.py
@@ -26,7 +26,7 @@
 import synapse.rest.admin
 from synapse.rest.client import login, notifications, receipts, room
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase
 
diff --git a/tests/rest/client/test_owned_state.py b/tests/rest/client/test_owned_state.py
index 386b95d616e..f927d74c373 100644
--- a/tests/rest/client/test_owned_state.py
+++ b/tests/rest/client/test_owned_state.py
@@ -10,7 +10,7 @@
 from synapse.rest.client import login, room
 from synapse.server import HomeServer
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase
 
diff --git a/tests/rest/client/test_password_policy.py b/tests/rest/client/test_password_policy.py
index 33bab684e33..5e98d8f1fdc 100644
--- a/tests/rest/client/test_password_policy.py
+++ b/tests/rest/client/test_password_policy.py
@@ -28,7 +28,7 @@
 from synapse.rest import admin
 from synapse.rest.client import account, login, password_policy, register
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/rest/client/test_power_levels.py b/tests/rest/client/test_power_levels.py
index 39ea9acef69..41610891fc0 100644
--- a/tests/rest/client/test_power_levels.py
+++ b/tests/rest/client/test_power_levels.py
@@ -27,7 +27,7 @@
 from synapse.rest import admin
 from synapse.rest.client import login, room, sync
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase
 
diff --git a/tests/rest/client/test_presence.py b/tests/rest/client/test_presence.py
index 7138cc92c26..5256c933e06 100644
--- a/tests/rest/client/test_presence.py
+++ b/tests/rest/client/test_presence.py
@@ -26,7 +26,7 @@
 from synapse.rest.client import presence
 from synapse.server import HomeServer
 from synapse.types import UserID
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.unittest import override_config
diff --git a/tests/rest/client/test_profile.py b/tests/rest/client/test_profile.py
index 936e573bcd4..18b3d3a089c 100644
--- a/tests/rest/client/test_profile.py
+++ b/tests/rest/client/test_profile.py
@@ -36,7 +36,7 @@
 from synapse.server import HomeServer
 from synapse.storage.databases.main.profile import MAX_PROFILE_SIZE
 from synapse.types import UserID
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.utils import USE_POSTGRES_FOR_TESTS
diff --git a/tests/rest/client/test_read_marker.py b/tests/rest/client/test_read_marker.py
index a27eb9453bc..c8bb0da5e64 100644
--- a/tests/rest/client/test_read_marker.py
+++ b/tests/rest/client/test_read_marker.py
@@ -25,7 +25,7 @@
 from synapse.rest import admin
 from synapse.rest.client import login, read_marker, register, room
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/rest/client/test_receipts.py b/tests/rest/client/test_receipts.py
index ae4818c412b..0c1b631b8e9 100644
--- a/tests/rest/client/test_receipts.py
+++ b/tests/rest/client/test_receipts.py
@@ -28,7 +28,7 @@
 from synapse.rest.client import login, receipts, room, sync
 from synapse.server import HomeServer
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/rest/client/test_redactions.py b/tests/rest/client/test_redactions.py
index d435a9e3935..e3ca108d03a 100644
--- a/tests/rest/client/test_redactions.py
+++ b/tests/rest/client/test_redactions.py
@@ -32,7 +32,7 @@
 from synapse.storage._base import db_to_json
 from synapse.storage.database import LoggingTransaction
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase, override_config
 
diff --git a/tests/rest/client/test_register.py b/tests/rest/client/test_register.py
index 70e005caf45..5dc3ef851a9 100644
--- a/tests/rest/client/test_register.py
+++ b/tests/rest/client/test_register.py
@@ -39,7 +39,7 @@
 from synapse.server import HomeServer
 from synapse.storage._base import db_to_json
 from synapse.types import JsonDict, UserID
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.server import ThreadedMemoryReactorClock
diff --git a/tests/rest/client/test_relations.py b/tests/rest/client/test_relations.py
index fd1e87296c3..21fb86367a3 100644
--- a/tests/rest/client/test_relations.py
+++ b/tests/rest/client/test_relations.py
@@ -30,7 +30,7 @@
 from synapse.rest.client import login, register, relations, room, sync
 from synapse.server import HomeServer
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.server import FakeChannel
diff --git a/tests/rest/client/test_rendezvous.py b/tests/rest/client/test_rendezvous.py
index 01401f73da8..160f8527051 100644
--- a/tests/rest/client/test_rendezvous.py
+++ b/tests/rest/client/test_rendezvous.py
@@ -28,7 +28,7 @@
 from synapse.rest.client import rendezvous
 from synapse.rest.synapse.client.rendezvous import MSC4108RendezvousSessionResource
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.unittest import override_config
diff --git a/tests/rest/client/test_reporting.py b/tests/rest/client/test_reporting.py
index 5e5af34b427..0fd02f65a6d 100644
--- a/tests/rest/client/test_reporting.py
+++ b/tests/rest/client/test_reporting.py
@@ -26,7 +26,7 @@
 from synapse.rest.client import login, reporting, room
 from synapse.server import HomeServer
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.unittest import override_config
diff --git a/tests/rest/client/test_retention.py b/tests/rest/client/test_retention.py
index 24b007f7791..7a816a66e07 100644
--- a/tests/rest/client/test_retention.py
+++ b/tests/rest/client/test_retention.py
@@ -27,7 +27,7 @@
 from synapse.rest.client import login, room
 from synapse.server import HomeServer
 from synapse.types import JsonDict, create_requester
-from synapse.util import Clock
+from synapse.util.clock import Clock
 from synapse.visibility import filter_events_for_client
 
 from tests import unittest
diff --git a/tests/rest/client/test_rooms.py b/tests/rest/client/test_rooms.py
index d3b5e26132d..feae5f77cdf 100644
--- a/tests/rest/client/test_rooms.py
+++ b/tests/rest/client/test_rooms.py
@@ -60,7 +60,7 @@
 )
 from synapse.server import HomeServer
 from synapse.types import JsonDict, RoomAlias, UserID, create_requester
-from synapse.util import Clock
+from synapse.util.clock import Clock
 from synapse.util.stringutils import random_string
 
 from tests import unittest
diff --git a/tests/rest/client/test_shadow_banned.py b/tests/rest/client/test_shadow_banned.py
index b990a8600be..bb240b943eb 100644
--- a/tests/rest/client/test_shadow_banned.py
+++ b/tests/rest/client/test_shadow_banned.py
@@ -34,7 +34,7 @@
 )
 from synapse.server import HomeServer
 from synapse.types import UserID, create_requester
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/rest/client/test_sync.py b/tests/rest/client/test_sync.py
index 7f3cf5affb3..e949bb69e63 100644
--- a/tests/rest/client/test_sync.py
+++ b/tests/rest/client/test_sync.py
@@ -36,7 +36,7 @@
 from synapse.rest.client import devices, knock, login, read_marker, receipts, room, sync
 from synapse.server import HomeServer
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.federation.transport.test_knocking import (
diff --git a/tests/rest/client/test_third_party_rules.py b/tests/rest/client/test_third_party_rules.py
index f14ca8237a3..4161faa11f9 100644
--- a/tests/rest/client/test_third_party_rules.py
+++ b/tests/rest/client/test_third_party_rules.py
@@ -36,7 +36,7 @@
 from synapse.rest.client import account, login, profile, room
 from synapse.server import HomeServer
 from synapse.types import JsonDict, Requester, StateMap
-from synapse.util import Clock
+from synapse.util.clock import Clock
 from synapse.util.frozenutils import unfreeze
 
 from tests import unittest
diff --git a/tests/rest/client/test_thread_subscriptions.py b/tests/rest/client/test_thread_subscriptions.py
index 3fbf3c5bfaa..5aae07ef507 100644
--- a/tests/rest/client/test_thread_subscriptions.py
+++ b/tests/rest/client/test_thread_subscriptions.py
@@ -20,7 +20,7 @@
 from synapse.rest.client import login, profile, room, thread_subscriptions
 from synapse.server import HomeServer
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/rest/client/test_transactions.py b/tests/rest/client/test_transactions.py
index 5f42acb391d..967f7836800 100644
--- a/tests/rest/client/test_transactions.py
+++ b/tests/rest/client/test_transactions.py
@@ -28,7 +28,7 @@
 from synapse.logging.context import SENTINEL_CONTEXT, LoggingContext, current_context
 from synapse.rest.client.transactions import CLEANUP_PERIOD_MS, HttpTransactionCache
 from synapse.types import ISynapseReactor, JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.utils import MockClock
diff --git a/tests/rest/client/test_typing.py b/tests/rest/client/test_typing.py
index ce2504156c8..19817d03213 100644
--- a/tests/rest/client/test_typing.py
+++ b/tests/rest/client/test_typing.py
@@ -27,7 +27,7 @@
 from synapse.rest.client import room
 from synapse.server import HomeServer
 from synapse.types import UserID
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/rest/client/test_upgrade_room.py b/tests/rest/client/test_upgrade_room.py
index 66fddc54759..da114e505d6 100644
--- a/tests/rest/client/test_upgrade_room.py
+++ b/tests/rest/client/test_upgrade_room.py
@@ -28,7 +28,7 @@
 from synapse.rest import admin
 from synapse.rest.client import login, room, room_upgrade_rest_servlet
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.server import FakeChannel
diff --git a/tests/rest/key/v2/test_remote_key_resource.py b/tests/rest/key/v2/test_remote_key_resource.py
index 3717d70b6b2..cf8241438c0 100644
--- a/tests/rest/key/v2/test_remote_key_resource.py
+++ b/tests/rest/key/v2/test_remote_key_resource.py
@@ -36,7 +36,7 @@
 from synapse.server import HomeServer
 from synapse.storage.keys import FetchKeyResult
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 from synapse.util.httpresourcetree import create_resource_tree
 from synapse.util.stringutils import random_string
 
diff --git a/tests/rest/media/test_domain_blocking.py b/tests/rest/media/test_domain_blocking.py
index 3feade4a4bb..9eb0222102d 100644
--- a/tests/rest/media/test_domain_blocking.py
+++ b/tests/rest/media/test_domain_blocking.py
@@ -25,7 +25,7 @@
 
 from synapse.media._base import FileInfo
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.test_utils import SMALL_PNG
diff --git a/tests/rest/media/test_url_preview.py b/tests/rest/media/test_url_preview.py
index e096780ce29..7c8d2fc9985 100644
--- a/tests/rest/media/test_url_preview.py
+++ b/tests/rest/media/test_url_preview.py
@@ -36,7 +36,7 @@
 from synapse.media.url_previewer import IMAGE_CACHE_EXPIRY_MS
 from synapse.server import HomeServer
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 from synapse.util.stringutils import parse_and_validate_mxc_uri
 
 from tests import unittest
diff --git a/tests/rest/synapse/mas/test_devices.py b/tests/rest/synapse/mas/test_devices.py
index 458878c13cb..6b7596f1c62 100644
--- a/tests/rest/synapse/mas/test_devices.py
+++ b/tests/rest/synapse/mas/test_devices.py
@@ -15,7 +15,7 @@
 
 from synapse.server import HomeServer
 from synapse.types import UserID
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import skip_unless
 from tests.utils import HAS_AUTHLIB
diff --git a/tests/rest/synapse/mas/test_users.py b/tests/rest/synapse/mas/test_users.py
index b236aceaf28..4e8cf907006 100644
--- a/tests/rest/synapse/mas/test_users.py
+++ b/tests/rest/synapse/mas/test_users.py
@@ -18,7 +18,7 @@
 from synapse.appservice import ApplicationService
 from synapse.server import HomeServer
 from synapse.types import JsonDict, UserID, create_requester
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import skip_unless
 from tests.utils import HAS_AUTHLIB
diff --git a/tests/server.py b/tests/server.py
index 7432db1ac85..f66ce070c63 100644
--- a/tests/server.py
+++ b/tests/server.py
@@ -103,7 +103,7 @@
 from synapse.storage.engines import BaseDatabaseEngine, create_engine
 from synapse.storage.prepare_database import prepare_database
 from synapse.types import ISynapseReactor, JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.utils import (
     LEAVE_DB,
diff --git a/tests/server_notices/__init__.py b/tests/server_notices/__init__.py
index 1d23a126deb..eca52930db2 100644
--- a/tests/server_notices/__init__.py
+++ b/tests/server_notices/__init__.py
@@ -19,7 +19,7 @@
 from synapse.rest.client import login, room, sync
 from synapse.server import HomeServer
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.unittest import override_config
diff --git a/tests/server_notices/test_consent.py b/tests/server_notices/test_consent.py
index db4a6370e89..45ed5b39d6b 100644
--- a/tests/server_notices/test_consent.py
+++ b/tests/server_notices/test_consent.py
@@ -25,7 +25,7 @@
 import synapse.rest.admin
 from synapse.rest.client import login, room, sync
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/server_notices/test_resource_limits_server_notices.py b/tests/server_notices/test_resource_limits_server_notices.py
index 0da12f14cde..dd38528a7d3 100644
--- a/tests/server_notices/test_resource_limits_server_notices.py
+++ b/tests/server_notices/test_resource_limits_server_notices.py
@@ -32,7 +32,7 @@
 )
 from synapse.server_notices.server_notices_sender import ServerNoticesSender
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.unittest import override_config
diff --git a/tests/state/test_v21.py b/tests/state/test_v21.py
index 5e46b69fef9..ff1715d4f7e 100644
--- a/tests/state/test_v21.py
+++ b/tests/state/test_v21.py
@@ -38,7 +38,7 @@
     resolve_events_with_store,
 )
 from synapse.types import StateMap
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.state.test_v2 import TestStateResolutionStore
diff --git a/tests/storage/databases/main/test_deviceinbox.py b/tests/storage/databases/main/test_deviceinbox.py
index d3ddeaa57e1..dbf362a3cc4 100644
--- a/tests/storage/databases/main/test_deviceinbox.py
+++ b/tests/storage/databases/main/test_deviceinbox.py
@@ -30,7 +30,7 @@
 from synapse.storage.databases.main.deviceinbox import (
     DEVICE_FEDERATION_INBOX_CLEANUP_DELAY_MS,
 )
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase
 
diff --git a/tests/storage/databases/main/test_end_to_end_keys.py b/tests/storage/databases/main/test_end_to_end_keys.py
index 3992fc3264c..d0dd8f866b9 100644
--- a/tests/storage/databases/main/test_end_to_end_keys.py
+++ b/tests/storage/databases/main/test_end_to_end_keys.py
@@ -26,7 +26,7 @@
 from synapse.storage._base import db_to_json
 from synapse.storage.database import LoggingTransaction
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase
 
diff --git a/tests/storage/databases/main/test_events_worker.py b/tests/storage/databases/main/test_events_worker.py
index f23609aee38..81a3447dbb6 100644
--- a/tests/storage/databases/main/test_events_worker.py
+++ b/tests/storage/databases/main/test_events_worker.py
@@ -38,8 +38,8 @@
     EventsWorkerStore,
 )
 from synapse.storage.types import Connection
-from synapse.util import Clock
 from synapse.util.async_helpers import yieldable_gather_results
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.test_utils.event_injection import create_event, inject_event
diff --git a/tests/storage/databases/main/test_lock.py b/tests/storage/databases/main/test_lock.py
index e18e0f27929..4296fcde13e 100644
--- a/tests/storage/databases/main/test_lock.py
+++ b/tests/storage/databases/main/test_lock.py
@@ -27,7 +27,7 @@
 
 from synapse.server import HomeServer
 from synapse.storage.databases.main.lock import _LOCK_TIMEOUT_MS, _RENEWAL_INTERVAL_MS
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/storage/databases/main/test_receipts.py b/tests/storage/databases/main/test_receipts.py
index 4141f868d60..d084f5c2ba5 100644
--- a/tests/storage/databases/main/test_receipts.py
+++ b/tests/storage/databases/main/test_receipts.py
@@ -27,7 +27,7 @@
 from synapse.rest.client import login, room
 from synapse.server import HomeServer
 from synapse.storage.database import LoggingTransaction
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase
 
diff --git a/tests/storage/databases/main/test_room.py b/tests/storage/databases/main/test_room.py
index dda4294e63d..4ed775ad769 100644
--- a/tests/storage/databases/main/test_room.py
+++ b/tests/storage/databases/main/test_room.py
@@ -28,7 +28,7 @@
 from synapse.rest.client import login, room
 from synapse.server import HomeServer
 from synapse.storage.databases.main.room import _BackgroundUpdates
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase
 
diff --git a/tests/storage/test__base.py b/tests/storage/test__base.py
index 7d260b79152..5e773a5545f 100644
--- a/tests/storage/test__base.py
+++ b/tests/storage/test__base.py
@@ -25,7 +25,7 @@
 from twisted.internet.testing import MemoryReactor
 
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/storage/test_account_data.py b/tests/storage/test_account_data.py
index 794cefd04de..13c4be988ee 100644
--- a/tests/storage/test_account_data.py
+++ b/tests/storage/test_account_data.py
@@ -26,7 +26,7 @@
 from synapse.api.constants import AccountDataTypes
 from synapse.api.errors import Codes, SynapseError
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/storage/test_appservice.py b/tests/storage/test_appservice.py
index 759fad6af16..b4df92c7a1d 100644
--- a/tests/storage/test_appservice.py
+++ b/tests/storage/test_appservice.py
@@ -39,7 +39,7 @@
     ApplicationServiceTransactionStore,
 )
 from synapse.types import DeviceListUpdates
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/storage/test_background_update.py b/tests/storage/test_background_update.py
index 89a3b54a25d..cf63b50c2f5 100644
--- a/tests/storage/test_background_update.py
+++ b/tests/storage/test_background_update.py
@@ -37,7 +37,7 @@
 from synapse.storage.database import LoggingTransaction
 from synapse.storage.engines import PostgresEngine, Sqlite3Engine
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.unittest import override_config
diff --git a/tests/storage/test_cleanup_extrems.py b/tests/storage/test_cleanup_extrems.py
index 94fb8e01a14..054e4a4d0b6 100644
--- a/tests/storage/test_cleanup_extrems.py
+++ b/tests/storage/test_cleanup_extrems.py
@@ -31,7 +31,7 @@
 from synapse.storage import prepare_database
 from synapse.storage.types import Cursor
 from synapse.types import UserID, create_requester
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase
 
diff --git a/tests/storage/test_client_ips.py b/tests/storage/test_client_ips.py
index de95272b527..1cd97a9dd7f 100644
--- a/tests/storage/test_client_ips.py
+++ b/tests/storage/test_client_ips.py
@@ -35,7 +35,7 @@
     DeviceLastConnectionInfo,
 )
 from synapse.types import UserID
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.server import make_request
diff --git a/tests/storage/test_database.py b/tests/storage/test_database.py
index 5e5937ff17c..fd6963bb82c 100644
--- a/tests/storage/test_database.py
+++ b/tests/storage/test_database.py
@@ -33,7 +33,7 @@
     LoggingTransaction,
     make_tuple_comparison_clause,
 )
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/storage/test_devices.py b/tests/storage/test_devices.py
index e8ea813668c..bd6fcd8eebe 100644
--- a/tests/storage/test_devices.py
+++ b/tests/storage/test_devices.py
@@ -27,7 +27,7 @@
 from synapse.api.constants import EduTypes
 from synapse.server import HomeServer
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase
 
diff --git a/tests/storage/test_directory.py b/tests/storage/test_directory.py
index 26bf6cf3918..4fb81e38cd3 100644
--- a/tests/storage/test_directory.py
+++ b/tests/storage/test_directory.py
@@ -23,7 +23,7 @@
 
 from synapse.server import HomeServer
 from synapse.types import RoomAlias, RoomID
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase
 
diff --git a/tests/storage/test_e2e_room_keys.py b/tests/storage/test_e2e_room_keys.py
index f390d11e411..2397d7b80e5 100644
--- a/tests/storage/test_e2e_room_keys.py
+++ b/tests/storage/test_e2e_room_keys.py
@@ -23,7 +23,7 @@
 
 from synapse.server import HomeServer
 from synapse.storage.databases.main.e2e_room_keys import RoomKey
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/storage/test_end_to_end_keys.py b/tests/storage/test_end_to_end_keys.py
index e46999022a0..24fdb0bf6de 100644
--- a/tests/storage/test_end_to_end_keys.py
+++ b/tests/storage/test_end_to_end_keys.py
@@ -22,7 +22,7 @@
 from twisted.internet.testing import MemoryReactor
 
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase
 
diff --git a/tests/storage/test_event_chain.py b/tests/storage/test_event_chain.py
index b2480a139dc..fe9bb7bcca0 100644
--- a/tests/storage/test_event_chain.py
+++ b/tests/storage/test_event_chain.py
@@ -37,7 +37,7 @@
 from synapse.storage.databases.main.events import _LinkMap
 from synapse.storage.types import Cursor
 from synapse.types import create_requester
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase
 
diff --git a/tests/storage/test_event_federation.py b/tests/storage/test_event_federation.py
index 2f79068f6b3..ee9cf3687f1 100644
--- a/tests/storage/test_event_federation.py
+++ b/tests/storage/test_event_federation.py
@@ -53,7 +53,8 @@
 from synapse.storage.types import Cursor
 from synapse.synapse_rust.events import EventInternalMetadata
 from synapse.types import JsonDict
-from synapse.util import Clock, json_encoder
+from synapse.util.clock import Clock
+from synapse.util.json import json_encoder
 
 import tests.unittest
 import tests.utils
diff --git a/tests/storage/test_event_push_actions.py b/tests/storage/test_event_push_actions.py
index 640490a6e57..30ba1ad94a4 100644
--- a/tests/storage/test_event_push_actions.py
+++ b/tests/storage/test_event_push_actions.py
@@ -29,7 +29,7 @@
 from synapse.server import HomeServer
 from synapse.storage.databases.main.event_push_actions import NotifCounts
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase
 
diff --git a/tests/storage/test_events.py b/tests/storage/test_events.py
index 6d2e4e4bbe6..93e9eab0390 100644
--- a/tests/storage/test_events.py
+++ b/tests/storage/test_events.py
@@ -32,7 +32,7 @@
 from synapse.rest.client import login, room
 from synapse.server import HomeServer
 from synapse.types import StateMap
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase
 
diff --git a/tests/storage/test_events_bg_updates.py b/tests/storage/test_events_bg_updates.py
index 7bbb5849a0f..a1375aa4ac8 100644
--- a/tests/storage/test_events_bg_updates.py
+++ b/tests/storage/test_events_bg_updates.py
@@ -20,7 +20,7 @@
 from synapse.api.constants import MAX_DEPTH
 from synapse.api.room_versions import RoomVersion, RoomVersions
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase
 
diff --git a/tests/storage/test_id_generators.py b/tests/storage/test_id_generators.py
index 9e949af482e..4c1311a00e1 100644
--- a/tests/storage/test_id_generators.py
+++ b/tests/storage/test_id_generators.py
@@ -35,7 +35,7 @@
     PostgresSequenceGenerator,
     SequenceGenerator,
 )
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase
 from tests.utils import USE_POSTGRES_FOR_TESTS
diff --git a/tests/storage/test_monthly_active_users.py b/tests/storage/test_monthly_active_users.py
index 78ef2e67a22..e684c6c1613 100644
--- a/tests/storage/test_monthly_active_users.py
+++ b/tests/storage/test_monthly_active_users.py
@@ -24,7 +24,7 @@
 
 from synapse.api.constants import UserTypes
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.unittest import default_config, override_config
diff --git a/tests/storage/test_profile.py b/tests/storage/test_profile.py
index 0f14e00e512..dbaf2986975 100644
--- a/tests/storage/test_profile.py
+++ b/tests/storage/test_profile.py
@@ -25,7 +25,7 @@
 from synapse.storage.database import LoggingTransaction
 from synapse.storage.engines import PostgresEngine
 from synapse.types import UserID
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/storage/test_purge.py b/tests/storage/test_purge.py
index 38d0cd6eb27..2894530d52d 100644
--- a/tests/storage/test_purge.py
+++ b/tests/storage/test_purge.py
@@ -25,7 +25,7 @@
 from synapse.server import HomeServer
 from synapse.types.state import StateFilter
 from synapse.types.storage import _BackgroundUpdates
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase
 
diff --git a/tests/storage/test_receipts.py b/tests/storage/test_receipts.py
index 8f7f7361750..10ded391f4b 100644
--- a/tests/storage/test_receipts.py
+++ b/tests/storage/test_receipts.py
@@ -26,7 +26,7 @@
 from synapse.api.constants import ReceiptTypes
 from synapse.server import HomeServer
 from synapse.types import UserID, create_requester
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.test_utils.event_injection import create_event
 from tests.unittest import HomeserverTestCase
diff --git a/tests/storage/test_redaction.py b/tests/storage/test_redaction.py
index a9c0d7d9a9e..7565376a592 100644
--- a/tests/storage/test_redaction.py
+++ b/tests/storage/test_redaction.py
@@ -31,7 +31,7 @@
 from synapse.server import HomeServer
 from synapse.synapse_rust.events import EventInternalMetadata
 from synapse.types import JsonDict, RoomID, UserID
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.utils import create_room
diff --git a/tests/storage/test_registration.py b/tests/storage/test_registration.py
index 992ccc779b8..7ee81fabb66 100644
--- a/tests/storage/test_registration.py
+++ b/tests/storage/test_registration.py
@@ -24,7 +24,7 @@
 from synapse.api.errors import ThreepidValidationError
 from synapse.server import HomeServer
 from synapse.types import JsonDict, UserID, UserInfo
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase, override_config
 
diff --git a/tests/storage/test_relations.py b/tests/storage/test_relations.py
index 0f3e3fe7eb3..96cee365f25 100644
--- a/tests/storage/test_relations.py
+++ b/tests/storage/test_relations.py
@@ -23,7 +23,7 @@
 
 from synapse.api.constants import MAIN_TIMELINE
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/storage/test_rollback_worker.py b/tests/storage/test_rollback_worker.py
index af69b93cf87..f61eb2e319e 100644
--- a/tests/storage/test_rollback_worker.py
+++ b/tests/storage/test_rollback_worker.py
@@ -29,7 +29,7 @@
 from synapse.storage.prepare_database import PrepareDatabaseException, prepare_database
 from synapse.storage.schema import SCHEMA_VERSION
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase
 
diff --git a/tests/storage/test_room.py b/tests/storage/test_room.py
index a8a75d29736..f8c5260fa2e 100644
--- a/tests/storage/test_room.py
+++ b/tests/storage/test_room.py
@@ -24,7 +24,7 @@
 from synapse.api.room_versions import RoomVersions
 from synapse.server import HomeServer
 from synapse.types import RoomAlias, RoomID, UserID
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase
 
diff --git a/tests/storage/test_room_search.py b/tests/storage/test_room_search.py
index f7eaa83ec61..e530e59fa64 100644
--- a/tests/storage/test_room_search.py
+++ b/tests/storage/test_room_search.py
@@ -33,7 +33,7 @@
 from synapse.storage.databases.main.search import Phrase, SearchToken, _tokenize_query
 from synapse.storage.engines import PostgresEngine
 from synapse.storage.engines.sqlite import Sqlite3Engine
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase, skip_unless
 from tests.utils import USE_POSTGRES_FOR_TESTS
diff --git a/tests/storage/test_roommember.py b/tests/storage/test_roommember.py
index fd489022a80..b8933d957b4 100644
--- a/tests/storage/test_roommember.py
+++ b/tests/storage/test_roommember.py
@@ -33,7 +33,7 @@
 from synapse.storage.databases.main.roommember import extract_heroes_from_room_summary
 from synapse.storage.roommember import MemberSummary
 from synapse.types import UserID, create_requester
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.server import TestHomeServer
diff --git a/tests/storage/test_sliding_sync_tables.py b/tests/storage/test_sliding_sync_tables.py
index 1a7a0b4c5c1..f0df166bab5 100644
--- a/tests/storage/test_sliding_sync_tables.py
+++ b/tests/storage/test_sliding_sync_tables.py
@@ -39,7 +39,7 @@
 )
 from synapse.types import create_requester
 from synapse.types.storage import _BackgroundUpdates
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.test_utils.event_injection import create_event
 from tests.unittest import HomeserverTestCase
diff --git a/tests/storage/test_state.py b/tests/storage/test_state.py
index cbf68b30327..bf6da715493 100644
--- a/tests/storage/test_state.py
+++ b/tests/storage/test_state.py
@@ -32,7 +32,7 @@
 from synapse.server import HomeServer
 from synapse.types import JsonDict, RoomID, StateMap, UserID
 from synapse.types.state import StateFilter
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase
 
diff --git a/tests/storage/test_state_deletion.py b/tests/storage/test_state_deletion.py
index 58cd1185679..d4079c372e7 100644
--- a/tests/storage/test_state_deletion.py
+++ b/tests/storage/test_state_deletion.py
@@ -20,7 +20,7 @@
 from synapse.rest import admin
 from synapse.rest.client import login, room
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.test_utils.event_injection import create_event
 from tests.unittest import HomeserverTestCase
diff --git a/tests/storage/test_stream.py b/tests/storage/test_stream.py
index ba2af1e044d..0777c254c0f 100644
--- a/tests/storage/test_stream.py
+++ b/tests/storage/test_stream.py
@@ -49,7 +49,7 @@
     UserID,
     create_requester,
 )
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.test_utils.event_injection import create_event
 from tests.unittest import FederatingHomeserverTestCase, HomeserverTestCase
diff --git a/tests/storage/test_thread_subscriptions.py b/tests/storage/test_thread_subscriptions.py
index 2ce369247fb..3f78308e455 100644
--- a/tests/storage/test_thread_subscriptions.py
+++ b/tests/storage/test_thread_subscriptions.py
@@ -24,7 +24,7 @@
 )
 from synapse.storage.engines.sqlite import Sqlite3Engine
 from synapse.types import EventOrderings
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/storage/test_transactions.py b/tests/storage/test_transactions.py
index 7b2ac9fce1e..a58c33aff66 100644
--- a/tests/storage/test_transactions.py
+++ b/tests/storage/test_transactions.py
@@ -22,7 +22,7 @@
 
 from synapse.server import HomeServer
 from synapse.storage.databases.main.transactions import DestinationRetryTimings
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase
 
diff --git a/tests/storage/test_txn_limit.py b/tests/storage/test_txn_limit.py
index 4722da50056..6bf4ce48f1a 100644
--- a/tests/storage/test_txn_limit.py
+++ b/tests/storage/test_txn_limit.py
@@ -23,7 +23,7 @@
 
 from synapse.server import HomeServer
 from synapse.storage.types import Cursor
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/storage/test_user_directory.py b/tests/storage/test_user_directory.py
index 255de298f3f..26e045135e4 100644
--- a/tests/storage/test_user_directory.py
+++ b/tests/storage/test_user_directory.py
@@ -37,7 +37,7 @@
 )
 from synapse.storage.roommember import ProfileInfo
 from synapse.types import UserID
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.server import ThreadedMemoryReactorClock
 from tests.test_utils.event_injection import inject_member_event
diff --git a/tests/storage/test_user_filters.py b/tests/storage/test_user_filters.py
index 8d928aa55c2..954a420cc0d 100644
--- a/tests/storage/test_user_filters.py
+++ b/tests/storage/test_user_filters.py
@@ -25,7 +25,7 @@
 from synapse.server import HomeServer
 from synapse.storage.database import LoggingTransaction
 from synapse.storage.engines import PostgresEngine
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/test_mau.py b/tests/test_mau.py
index 1000870aa91..fa98242bf75 100644
--- a/tests/test_mau.py
+++ b/tests/test_mau.py
@@ -30,7 +30,7 @@
 from synapse.rest.client import register, sync
 from synapse.server import HomeServer
 from synapse.types import JsonDict, UserID
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.unittest import override_config
diff --git a/tests/test_phone_home.py b/tests/test_phone_home.py
index 0b230ed0f50..ab21a5dde4f 100644
--- a/tests/test_phone_home.py
+++ b/tests/test_phone_home.py
@@ -29,7 +29,7 @@
 from synapse.rest.client import login, sync
 from synapse.server import HomeServer
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests.unittest import HomeserverTestCase
 
diff --git a/tests/test_server.py b/tests/test_server.py
index 0aa35845187..69efceafe84 100644
--- a/tests/test_server.py
+++ b/tests/test_server.py
@@ -36,8 +36,8 @@
 from synapse.http.site import SynapseRequest, SynapseSite
 from synapse.logging.context import make_deferred_yieldable
 from synapse.types import JsonDict
-from synapse.util import Clock
 from synapse.util.cancellation import cancellable
+from synapse.util.clock import Clock
 
 from tests import unittest
 from tests.http.server._base import test_disconnect
diff --git a/tests/test_state.py b/tests/test_state.py
index adb72b07304..16446c16bc0 100644
--- a/tests/test_state.py
+++ b/tests/test_state.py
@@ -43,7 +43,7 @@
 from synapse.state import StateHandler, StateResolutionHandler, _make_state_cache_entry
 from synapse.types import MutableStateMap, StateMap
 from synapse.types.state import StateFilter
-from synapse.util import Clock
+from synapse.util.clock import Clock
 from synapse.util.macaroons import MacaroonGenerator
 
 from tests import unittest
diff --git a/tests/test_terms_auth.py b/tests/test_terms_auth.py
index 8065ae4b8ab..ec479214231 100644
--- a/tests/test_terms_auth.py
+++ b/tests/test_terms_auth.py
@@ -26,7 +26,7 @@
 from synapse.rest.client.register import register_servlets
 from synapse.server import HomeServer
 from synapse.types import JsonDict
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from tests import unittest
 
diff --git a/tests/test_utils/oidc.py b/tests/test_utils/oidc.py
index 5bf5e5cb0cc..f2de8bded5d 100644
--- a/tests/test_utils/oidc.py
+++ b/tests/test_utils/oidc.py
@@ -33,7 +33,7 @@
 from twisted.web.iweb import IResponse
 
 from synapse.server import HomeServer
-from synapse.util import Clock
+from synapse.util.clock import Clock
 from synapse.util.stringutils import random_string
 
 from tests.test_utils import FakeResponse
diff --git a/tests/test_visibility.py b/tests/test_visibility.py
index 285e28e0f91..9a8cad6454b 100644
--- a/tests/test_visibility.py
+++ b/tests/test_visibility.py
@@ -31,7 +31,7 @@
 from synapse.rest.client import login, room
 from synapse.server import HomeServer
 from synapse.types import create_requester
-from synapse.util import Clock
+from synapse.util.clock import Clock
 from synapse.visibility import filter_events_for_client, filter_events_for_server
 
 from tests import unittest
diff --git a/tests/unittest.py b/tests/unittest.py
index 5e6957dc6d2..8ae217feb27 100644
--- a/tests/unittest.py
+++ b/tests/unittest.py
@@ -81,7 +81,7 @@
 from synapse.server import HomeServer
 from synapse.storage.keys import FetchKeyResult
 from synapse.types import JsonDict, Requester, UserID, create_requester
-from synapse.util import Clock
+from synapse.util.clock import Clock
 from synapse.util.httpresourcetree import create_resource_tree
 
 from tests.server import (
diff --git a/tests/util/test_expiring_cache.py b/tests/util/test_expiring_cache.py
index 75bf50e644b..bfcc6cd12f2 100644
--- a/tests/util/test_expiring_cache.py
+++ b/tests/util/test_expiring_cache.py
@@ -21,8 +21,8 @@
 
 from typing import List, cast
 
-from synapse.util import Clock
 from synapse.util.caches.expiringcache import ExpiringCache
+from synapse.util.clock import Clock
 
 from tests.utils import MockClock
 
diff --git a/tests/util/test_logcontext.py b/tests/util/test_logcontext.py
index af36e685d7c..43912d05dae 100644
--- a/tests/util/test_logcontext.py
+++ b/tests/util/test_logcontext.py
@@ -34,7 +34,7 @@
     run_in_background,
 )
 from synapse.types import ISynapseReactor
-from synapse.util import Clock
+from synapse.util.clock import Clock
 
 from .. import unittest
 
diff --git a/tests/util/test_task_scheduler.py b/tests/util/test_task_scheduler.py
index 2171f91b4d0..e97f0ed6111 100644
--- a/tests/util/test_task_scheduler.py
+++ b/tests/util/test_task_scheduler.py
@@ -25,7 +25,7 @@
 
 from synapse.server import HomeServer
 from synapse.types import JsonMapping, ScheduledTask, TaskStatus
-from synapse.util import Clock
+from synapse.util.clock import Clock
 from synapse.util.task_scheduler import TaskScheduler
 
 from tests.replication._base import BaseMultiWorkerStreamTestCase

From 2d1331f0e4ff2ef76d839dc52cd849bb1fadffaf Mon Sep 17 00:00:00 2001
From: Eric Eastwood <erice@element.io>
Date: Fri, 19 Sep 2025 14:03:50 -0500
Subject: [PATCH 03/12] Add `Clock.call_when_running(...)`

---
 .../http/federation/well_known_resolver.py    |  4 +-
 synapse/http/server.py                        |  7 +--
 synapse/types/__init__.py                     | 16 +++++-
 synapse/util/async_helpers.py                 |  3 +-
 synapse/util/caches/lrucache.py               |  4 +-
 synapse/util/clock.py                         | 54 ++++++++++++++++++-
 tests/logging/test_opentracing.py             | 16 +++++-
 tests/test_terms_auth.py                      | 11 +---
 8 files changed, 93 insertions(+), 22 deletions(-)

diff --git a/synapse/http/federation/well_known_resolver.py b/synapse/http/federation/well_known_resolver.py
index ac2d0addf79..49e58c82288 100644
--- a/synapse/http/federation/well_known_resolver.py
+++ b/synapse/http/federation/well_known_resolver.py
@@ -27,7 +27,6 @@
 import attr
 
 from twisted.internet import defer
-from twisted.internet.interfaces import IReactorTime
 from twisted.web.client import RedirectAgent
 from twisted.web.http import stringToDatetime
 from twisted.web.http_headers import Headers
@@ -35,6 +34,7 @@
 
 from synapse.http.client import BodyExceededMaxSize, read_body_with_max_size
 from synapse.logging.context import make_deferred_yieldable
+from synapse.types import ISynapseThreadlessReactor
 from synapse.util.caches.ttlcache import TTLCache
 from synapse.util.clock import Clock
 from synapse.util.json import json_decoder
@@ -89,7 +89,7 @@ class WellKnownResolver:
     def __init__(
         self,
         server_name: str,
-        reactor: IReactorTime,
+        reactor: ISynapseThreadlessReactor,
         agent: IAgent,
         user_agent: bytes,
         well_known_cache: Optional[TTLCache[bytes, Optional[bytes]]] = None,
diff --git a/synapse/http/server.py b/synapse/http/server.py
index f04c55d4576..0b987f6aa9a 100644
--- a/synapse/http/server.py
+++ b/synapse/http/server.py
@@ -52,10 +52,11 @@
 
 from twisted.internet import defer, interfaces, reactor
 from twisted.internet.defer import CancelledError
-from twisted.internet.interfaces import IReactorTime
 from twisted.python import failure
 from twisted.web import resource
 
+from synapse.types import ISynapseThreadlessReactor
+
 try:
     from twisted.web.pages import notFound
 except ImportError:
@@ -411,7 +412,7 @@ def __init__(
         clock: Optional[Clock] = None,
     ):
         if clock is None:
-            clock = Clock(cast(IReactorTime, reactor))
+            clock = Clock(cast(ISynapseThreadlessReactor, reactor))
 
         super().__init__(clock, extract_context)
         self.canonical_json = canonical_json
@@ -590,7 +591,7 @@ def __init__(
         clock: Optional[Clock] = None,
     ):
         if clock is None:
-            clock = Clock(cast(IReactorTime, reactor))
+            clock = Clock(cast(ISynapseThreadlessReactor, reactor))
 
         super().__init__(clock, extract_context)
 
diff --git a/synapse/types/__init__.py b/synapse/types/__init__.py
index 2d5b07ab8fa..0386cb77d62 100644
--- a/synapse/types/__init__.py
+++ b/synapse/types/__init__.py
@@ -116,13 +116,27 @@
 
 # Note that this seems to require inheriting *directly* from Interface in order
 # for mypy-zope to realize it is an interface.
-class ISynapseReactor(
+class ISynapseThreadlessReactor(
     IReactorTCP,
     IReactorSSL,
     IReactorUNIX,
     IReactorPluggableNameResolver,
     IReactorTime,
     IReactorCore,
+    Interface,
+):
+    """
+    The interfaces necessary for Synapse to function (without threads).
+
+    Helpful because we use `twisted.internet.testing.MemoryReactorClock` in tests which
+    doesn't implement `IReactorThreads`.
+    """
+
+
+# Note that this seems to require inheriting *directly* from Interface in order
+# for mypy-zope to realize it is an interface.
+class ISynapseReactor(
+    ISynapseThreadlessReactor,
     IReactorThreads,
     Interface,
 ):
diff --git a/synapse/util/async_helpers.py b/synapse/util/async_helpers.py
index 51bb1bf165d..1c343f8d3e5 100644
--- a/synapse/util/async_helpers.py
+++ b/synapse/util/async_helpers.py
@@ -65,6 +65,7 @@
     run_coroutine_in_background,
     run_in_background,
 )
+from synapse.types import ISynapseThreadlessReactor
 from synapse.util.clock import Clock
 
 logger = logging.getLogger(__name__)
@@ -566,7 +567,7 @@ def __init__(
         if not clock:
             from twisted.internet import reactor
 
-            clock = Clock(cast(IReactorTime, reactor))
+            clock = Clock(cast(ISynapseThreadlessReactor, reactor))
         self._clock = clock
         self.max_count = max_count
 
diff --git a/synapse/util/caches/lrucache.py b/synapse/util/caches/lrucache.py
index d1a338ab99d..187380c433e 100644
--- a/synapse/util/caches/lrucache.py
+++ b/synapse/util/caches/lrucache.py
@@ -46,13 +46,13 @@
 )
 
 from twisted.internet import defer, reactor
-from twisted.internet.interfaces import IReactorTime
 
 from synapse.config import cache as cache_config
 from synapse.metrics.background_process_metrics import (
     run_as_background_process,
 )
 from synapse.metrics.jemalloc import get_jemalloc_stats
+from synapse.types import ISynapseThreadlessReactor
 from synapse.util import caches
 from synapse.util.caches import CacheMetric, EvictionReason, register_cache
 from synapse.util.caches.treecache import (
@@ -497,7 +497,7 @@ def __init__(
         # Default `clock` to something sensible. Note that we rename it to
         # `real_clock` so that mypy doesn't think its still `Optional`.
         if clock is None:
-            real_clock = Clock(cast(IReactorTime, reactor))
+            real_clock = Clock(cast(ISynapseThreadlessReactor, reactor))
         else:
             real_clock = clock
 
diff --git a/synapse/util/clock.py b/synapse/util/clock.py
index 9fb3fc25096..5c59d4415f8 100644
--- a/synapse/util/clock.py
+++ b/synapse/util/clock.py
@@ -23,10 +23,11 @@
 from typing_extensions import ParamSpec
 
 from twisted.internet import defer, task
-from twisted.internet.interfaces import IDelayedCall, IReactorTime
+from twisted.internet.interfaces import IDelayedCall
 from twisted.internet.task import LoopingCall
 
 from synapse.logging import context
+from synapse.types import ISynapseThreadlessReactor
 from synapse.util import log_failure
 
 P = ParamSpec("P")
@@ -41,7 +42,7 @@ class Clock:
         reactor: The Twisted reactor to use.
     """
 
-    _reactor: IReactorTime = attr.ib()
+    _reactor: ISynapseThreadlessReactor = attr.ib()
 
     async def sleep(self, seconds: float) -> None:
         d: defer.Deferred[float] = defer.Deferred()
@@ -150,3 +151,52 @@ def cancel_call_later(self, timer: IDelayedCall, ignore_errs: bool = False) -> N
         except Exception:
             if not ignore_errs:
                 raise
+
+    def call_when_running(
+        self,
+        callback: Callable[P, object],
+        *args: P.args,
+        **kwargs: P.kwargs,
+    ) -> None:
+        """
+        Call a function when the reactor is running.
+
+        If the reactor has not started, the callable will be scheduled to run when it
+        does start. Otherwise, the callable will be invoked immediately.
+
+        Args:
+            callback: Function to call
+            *args: Postional arguments to pass to function.
+            **kwargs: Key arguments to pass to function.
+        """
+
+        def wrapped_callback(*args: Any, **kwargs: Any) -> None:
+            assert context.current_context() is context.SENTINEL_CONTEXT, (
+                "Expected `call_later` callback from the reactor to start with the sentinel logcontext "
+                f"but saw {context.current_context()}. In other words, another task shouldn't have "
+                "leaked their logcontext to us."
+            )
+
+            # Because this is a callback from the reactor, we will be using the
+            # `sentinel` log context at this point. We want the function to log with
+            # some logcontext as we want to know which server the logs came from.
+            #
+            # We use `PreserveLoggingContext` to prevent our new `call_later`
+            # logcontext from finishing as soon as we exit this function, in case `f`
+            # returns an awaitable/deferred which would continue running and may try to
+            # restore the `loop_call` context when it's done (because it's trying to
+            # adhere to the Synapse logcontext rules.)
+            #
+            # This also ensures that we return to the `sentinel` context when we exit
+            # this function and yield control back to the reactor to avoid leaking the
+            # current logcontext to the reactor (which would then get picked up and
+            # associated with the next thing the reactor does)
+            with context.PreserveLoggingContext(
+                context.LoggingContext("call_when_running")
+            ):
+                # We use `run_in_background` to reset the logcontext after `f` (or the
+                # awaitable returned by `f`) completes to avoid leaking the current
+                # logcontext to the reactor
+                context.run_in_background(callback, *args, **kwargs)
+
+        self._reactor.callWhenRunning(wrapped_callback, *args, **kwargs)
diff --git a/tests/logging/test_opentracing.py b/tests/logging/test_opentracing.py
index 951102701cb..d102d501386 100644
--- a/tests/logging/test_opentracing.py
+++ b/tests/logging/test_opentracing.py
@@ -159,7 +159,13 @@ def test_nested_spans(self) -> None:
     def test_overlapping_spans(self) -> None:
         """Overlapping spans which are not neatly nested should work"""
         reactor = MemoryReactorClock()
-        clock = Clock(reactor)
+        # type-ignore: mypy-zope doesn't seem to recognise that `MemoryReactorClock`
+        # implements `ISynapseThreadlessReactor` (combination of the normal Twisted
+        # Reactor/Clock interfaces), via inheritance from
+        # `twisted.internet.testing.MemoryReactor` and `twisted.internet.testing.Clock`
+        clock = Clock(
+            reactor  # type: ignore[arg-type]
+        )
 
         scopes = []
 
@@ -223,7 +229,13 @@ def test_run_in_background_active_scope_still_available(self) -> None:
         parent.
         """
         reactor = MemoryReactorClock()
-        clock = Clock(reactor)
+        # type-ignore: mypy-zope doesn't seem to recognise that `MemoryReactorClock`
+        # implements `ISynapseThreadlessReactor` (combination of the normal Twisted
+        # Reactor/Clock interfaces), via inheritance from
+        # `twisted.internet.testing.MemoryReactor` and `twisted.internet.testing.Clock`
+        clock = Clock(
+            reactor  # type: ignore[arg-type]
+        )
 
         scope_map: Dict[str, opentracing.Scope] = {}
 
diff --git a/tests/test_terms_auth.py b/tests/test_terms_auth.py
index ec479214231..bd5e6520ac1 100644
--- a/tests/test_terms_auth.py
+++ b/tests/test_terms_auth.py
@@ -20,8 +20,7 @@
 
 from unittest.mock import Mock
 
-from twisted.internet.interfaces import IReactorTime
-from twisted.internet.testing import MemoryReactor, MemoryReactorClock
+from twisted.internet.testing import MemoryReactor
 
 from synapse.rest.client.register import register_servlets
 from synapse.server import HomeServer
@@ -49,13 +48,7 @@ def default_config(self) -> JsonDict:
         )
         return config
 
-    def prepare(
-        self, reactor: MemoryReactor, clock: Clock, homeserver: HomeServer
-    ) -> None:
-        # type-ignore: mypy-zope doesn't seem to recognise that MemoryReactorClock
-        # implements IReactorTime, via inheritance from twisted.internet.testing.Clock
-        self.clock: IReactorTime = MemoryReactorClock()  # type: ignore[assignment]
-        self.hs_clock = Clock(self.clock)
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.url = "/_matrix/client/r0/register"
         self.registration_handler = Mock()
         self.auth_handler = Mock()

From f1e6887d14cd2ab94fce2bbd0fed08f6b49e0ace Mon Sep 17 00:00:00 2001
From: Eric Eastwood <erice@element.io>
Date: Fri, 19 Sep 2025 14:28:30 -0500
Subject: [PATCH 04/12] Add lint to prefer `Clock.call_when_running`

---
 scripts-dev/mypy_synapse_plugin.py | 40 ++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/scripts-dev/mypy_synapse_plugin.py b/scripts-dev/mypy_synapse_plugin.py
index 610dec415af..439a75fc7e2 100644
--- a/scripts-dev/mypy_synapse_plugin.py
+++ b/scripts-dev/mypy_synapse_plugin.py
@@ -68,6 +68,12 @@
     category="per-homeserver-tenant-metrics",
 )
 
+PREFER_SYNAPSE_CLOCK_CALL_WHEN_RUNNING = ErrorCode(
+    "prefer-synapse-clock-call-when-running",
+    "`synapse.util.Clock.call_when_running` should be used instead of `reactor.callWhenRunning`",
+    category="synapse-reactor-clock",
+)
+
 
 class Sentinel(enum.Enum):
     # defining a sentinel in this way allows mypy to correctly handle the
@@ -229,9 +235,43 @@ def get_method_signature_hook(
         ):
             return check_is_cacheable_wrapper
 
+        if fullname in (
+            "twisted.internet.interfaces.IReactorCore.callWhenRunning",
+            "synapse.types.ISynapseThreadlessReactor.callWhenRunning",
+            "synapse.types.ISynapseReactor.callWhenRunning",
+        ):
+            return check_call_when_running
+
         return None
 
 
+def check_call_when_running(ctx: MethodSigContext) -> CallableType:
+    """
+    Ensure that the `reactor.callWhenRunning` callsites aren't used.
+
+    `synapse.util.Clock.call_when_running` should always be used instead of
+    `reactor.callWhenRunning`.
+
+    Since `reactor.callWhenRunning` is a reactor callback, the callback will start out
+    with the sentinel logcontext. `synapse.util.Clock` starts a default logcontext as we
+    want to know which server the logs came from.
+
+    Args:
+        ctx: The `FunctionSigContext` from mypy.
+    """
+    signature: CallableType = ctx.default_signature
+    ctx.api.fail(
+        (
+            "Expected all `reactor.callWhenRunning` calls to use `synapse.util.Clock.call_when_running` instead. "
+            "This is so all Synapse code runs with a logcontext as we want to know which server the logs came from."
+        ),
+        ctx.context,
+        code=PREFER_SYNAPSE_CLOCK_CALL_WHEN_RUNNING,
+    )
+
+    return signature
+
+
 def analyze_prometheus_metric_classes(ctx: ClassDefContext) -> None:
     """
     Cross-check the list of Prometheus metric classes against the

From 12e7cf4487fe2cf9084f6197cc2e276be6d0a536 Mon Sep 17 00:00:00 2001
From: Eric Eastwood <erice@element.io>
Date: Fri, 19 Sep 2025 14:57:48 -0500
Subject: [PATCH 05/12] Fix `reactor.callWhenRunning` lints

---
 synapse/_scripts/synapse_port_db.py         | 59 ++++++++-------------
 synapse/_scripts/update_synapse_database.py |  2 +-
 synapse/app/_base.py                        |  5 +-
 synapse/app/generic_worker.py               |  2 +-
 synapse/app/homeserver.py                   |  2 +-
 synapse/handlers/deactivate_account.py      |  2 +-
 synapse/handlers/device.py                  |  2 +-
 synapse/logging/handlers.py                 | 14 ++++-
 synapse/util/clock.py                       |  4 +-
 synmark/__main__.py                         |  5 +-
 10 files changed, 49 insertions(+), 48 deletions(-)

diff --git a/synapse/_scripts/synapse_port_db.py b/synapse/_scripts/synapse_port_db.py
index a4591014f4e..211ed2e8638 100755
--- a/synapse/_scripts/synapse_port_db.py
+++ b/synapse/_scripts/synapse_port_db.py
@@ -58,7 +58,8 @@
     make_deferred_yieldable,
     run_in_background,
 )
-from synapse.notifier import ReplicationNotifier
+from synapse.server import HomeServer
+from synapse.storage import DataStore
 from synapse.storage.database import DatabasePool, LoggingTransaction, make_conn
 from synapse.storage.databases.main import FilteringWorkerStore
 from synapse.storage.databases.main.account_data import AccountDataWorkerStore
@@ -99,8 +100,6 @@
 from synapse.storage.prepare_database import prepare_database
 from synapse.types import ISynapseReactor
 from synapse.util import SYNAPSE_VERSION
-from synapse.util.clock import Clock
-from synapse.util.stringutils import random_string
 
 # Cast safety: Twisted does some naughty magic which replaces the
 # twisted.internet.reactor module with a Reactor instance at runtime.
@@ -319,31 +318,16 @@ def set_room_is_public(self, room_id: str, is_public: bool) -> NoReturn:
         )
 
 
-class MockHomeserver:
-    def __init__(self, config: HomeServerConfig):
-        self.clock = Clock(reactor)
-        self.config = config
-        self.hostname = config.server.server_name
-        self.version_string = SYNAPSE_VERSION
-        self.instance_id = random_string(5)
-
-    def get_clock(self) -> Clock:
-        return self.clock
-
-    def get_reactor(self) -> ISynapseReactor:
-        return reactor
-
-    def get_instance_id(self) -> str:
-        return self.instance_id
-
-    def get_instance_name(self) -> str:
-        return "master"
+class MockHomeserver(HomeServer):
+    DATASTORE_CLASS = DataStore
 
-    def should_send_federation(self) -> bool:
-        return False
-
-    def get_replication_notifier(self) -> ReplicationNotifier:
-        return ReplicationNotifier()
+    def __init__(self, config: HomeServerConfig):
+        super().__init__(
+            hostname=config.server.server_name,
+            config=config,
+            reactor=reactor,
+            version_string=f"Synapse/{SYNAPSE_VERSION}",
+        )
 
 
 class Porter:
@@ -352,12 +336,12 @@ def __init__(
         sqlite_config: Dict[str, Any],
         progress: "Progress",
         batch_size: int,
-        hs_config: HomeServerConfig,
+        hs: HomeServer,
     ):
         self.sqlite_config = sqlite_config
         self.progress = progress
         self.batch_size = batch_size
-        self.hs_config = hs_config
+        self.hs = hs
 
     async def setup_table(self, table: str) -> Tuple[str, int, int, int, int]:
         if table in APPEND_ONLY_TABLES:
@@ -677,8 +661,7 @@ def build_db_store(
 
         engine = create_engine(db_config.config)
 
-        hs = MockHomeserver(self.hs_config)
-        server_name = hs.hostname
+        server_name = self.hs.hostname
 
         with make_conn(
             db_config=db_config,
@@ -689,16 +672,16 @@ def build_db_store(
             engine.check_database(
                 db_conn, allow_outdated_version=allow_outdated_version
             )
-            prepare_database(db_conn, engine, config=self.hs_config)
+            prepare_database(db_conn, engine, config=self.hs.config)
             # Type safety: ignore that we're using Mock homeservers here.
             store = Store(
                 DatabasePool(
-                    hs,  # type: ignore[arg-type]
+                    self.hs,
                     db_config,
                     engine,
                 ),
                 db_conn,
-                hs,  # type: ignore[arg-type]
+                self.hs,
             )
             db_conn.commit()
 
@@ -796,7 +779,7 @@ async def run(self) -> None:
                 return
 
             self.postgres_store = self.build_db_store(
-                self.hs_config.database.get_single_database()
+                self.hs.config.database.get_single_database()
             )
 
             await self.remove_ignored_background_updates_from_database()
@@ -1585,6 +1568,8 @@ def main() -> None:
     config = HomeServerConfig()
     config.parse_config_dict(hs_config, "", "")
 
+    hs = MockHomeserver(hs_config)
+
     def start(stdscr: Optional["curses.window"] = None) -> None:
         progress: Progress
         if stdscr:
@@ -1596,7 +1581,7 @@ def start(stdscr: Optional["curses.window"] = None) -> None:
             sqlite_config=sqlite_config,
             progress=progress,
             batch_size=args.batch_size,
-            hs_config=config,
+            hs=hs,
         )
 
         @defer.inlineCallbacks
@@ -1604,7 +1589,7 @@ def run() -> Generator["defer.Deferred[Any]", Any, None]:
             with LoggingContext("synapse_port_db_run"):
                 yield defer.ensureDeferred(porter.run())
 
-        reactor.callWhenRunning(run)
+        hs.get_clock().call_when_running(run)
 
         reactor.run()
 
diff --git a/synapse/_scripts/update_synapse_database.py b/synapse/_scripts/update_synapse_database.py
index 3624db3544e..caaecda1617 100644
--- a/synapse/_scripts/update_synapse_database.py
+++ b/synapse/_scripts/update_synapse_database.py
@@ -74,7 +74,7 @@ def run() -> None:
             )
         )
 
-    reactor.callWhenRunning(run)
+    hs.get_clock().call_when_running(run)
 
     reactor.run()
 
diff --git a/synapse/app/_base.py b/synapse/app/_base.py
index cf3d260e65e..02c56496bfb 100644
--- a/synapse/app/_base.py
+++ b/synapse/app/_base.py
@@ -241,7 +241,7 @@ def redirect_stdio_to_logs() -> None:
 
 
 def register_start(
-    cb: Callable[P, Awaitable], *args: P.args, **kwargs: P.kwargs
+    hs: "HomeServer", cb: Callable[P, Awaitable], *args: P.args, **kwargs: P.kwargs
 ) -> None:
     """Register a callback with the reactor, to be called once it is running
 
@@ -278,7 +278,8 @@ async def wrapper() -> None:
             # on as normal.
             os._exit(1)
 
-    reactor.callWhenRunning(lambda: defer.ensureDeferred(wrapper()))
+    clock = hs.get_clock()
+    clock.call_when_running(lambda: defer.ensureDeferred(wrapper()))
 
 
 def listen_metrics(bind_addresses: StrCollection, port: int) -> None:
diff --git a/synapse/app/generic_worker.py b/synapse/app/generic_worker.py
index 543b26d8ba8..4563690b6dd 100644
--- a/synapse/app/generic_worker.py
+++ b/synapse/app/generic_worker.py
@@ -360,7 +360,7 @@ async def start() -> None:
         with LoggingContext("start"):
             await _base.start(hs)
 
-    register_start(start)
+    register_start(hs, start)
 
     # redirect stdio to the logs, if configured.
     if not hs.config.logging.no_redirect_stdio:
diff --git a/synapse/app/homeserver.py b/synapse/app/homeserver.py
index dfc4a007197..3dffe6166b6 100644
--- a/synapse/app/homeserver.py
+++ b/synapse/app/homeserver.py
@@ -389,7 +389,7 @@ async def start() -> None:
 
             hs.get_datastores().main.db_pool.updates.start_doing_background_updates()
 
-    register_start(start)
+    register_start(hs, start)
 
     return hs
 
diff --git a/synapse/handlers/deactivate_account.py b/synapse/handlers/deactivate_account.py
index e4169321ccc..c0684380a70 100644
--- a/synapse/handlers/deactivate_account.py
+++ b/synapse/handlers/deactivate_account.py
@@ -62,7 +62,7 @@ def __init__(self, hs: "HomeServer"):
         # Start the user parter loop so it can resume parting users from rooms where
         # it left off (if it has work left to do).
         if hs.config.worker.worker_app is None:
-            hs.get_reactor().callWhenRunning(self._start_user_parting)
+            hs.get_clock().call_when_running(self._start_user_parting)
         else:
             self._notify_account_deactivated_client = (
                 ReplicationNotifyAccountDeactivatedServlet.make_client(hs)
diff --git a/synapse/handlers/device.py b/synapse/handlers/device.py
index acae34e71f5..65b8a95f8e5 100644
--- a/synapse/handlers/device.py
+++ b/synapse/handlers/device.py
@@ -1002,7 +1002,7 @@ def __init__(self, hs: "HomeServer"):
         # rolling-restarting Synapse.
         if self._is_main_device_list_writer:
             # On start up check if there are any updates pending.
-            hs.get_reactor().callWhenRunning(self._handle_new_device_update_async)
+            hs.get_clock().call_when_running(self._handle_new_device_update_async)
             self.device_list_updater = DeviceListUpdater(hs, self)
             hs.get_federation_registry().register_edu_handler(
                 EduTypes.DEVICE_LIST_UPDATE,
diff --git a/synapse/logging/handlers.py b/synapse/logging/handlers.py
index dec2a2c3dd1..b7945aac728 100644
--- a/synapse/logging/handlers.py
+++ b/synapse/logging/handlers.py
@@ -60,8 +60,18 @@ def on_reactor_running() -> None:
         else:
             reactor_to_use = reactor
 
-        # call our hook when the reactor start up
-        reactor_to_use.callWhenRunning(on_reactor_running)
+        # Call our hook when the reactor start up
+        #
+        # type-ignore: Ideally, we'd use `Clock.call_when_running(...)`, but
+        # `PeriodicallyFlushingMemoryHandler` is instantiated via Python logging
+        # configuration, so it's not straightforward to pass in the homeserver's clock
+        # (and we don't want to burden other peoples logging config with the details).
+        #
+        # The important reason why we want to use `Clock.call_when_running` is so that
+        # the callback runs with a logcontext as we want to know which server the logs
+        # came from. But since we don't log anything in the callback, it's safe to
+        # ignore the lint here.
+        reactor_to_use.callWhenRunning(on_reactor_running)  # type: ignore[prefer-synapse-clock-call-when-running]
 
     def shouldFlush(self, record: LogRecord) -> bool:
         """
diff --git a/synapse/util/clock.py b/synapse/util/clock.py
index 5c59d4415f8..6a72197d2a0 100644
--- a/synapse/util/clock.py
+++ b/synapse/util/clock.py
@@ -199,4 +199,6 @@ def wrapped_callback(*args: Any, **kwargs: Any) -> None:
                 # logcontext to the reactor
                 context.run_in_background(callback, *args, **kwargs)
 
-        self._reactor.callWhenRunning(wrapped_callback, *args, **kwargs)
+        # We can ignore the lint here since this class is the one location
+        # callWhenRunning should be called.
+        self._reactor.callWhenRunning(wrapped_callback, *args, **kwargs)  # type: ignore[prefer-synapse-clock-call-when-running]
diff --git a/synmark/__main__.py b/synmark/__main__.py
index 4944c2f3b07..82717c4fc74 100644
--- a/synmark/__main__.py
+++ b/synmark/__main__.py
@@ -62,7 +62,10 @@ def on_done(res: T) -> T:
                 return res
 
             d.addBoth(on_done)
-            reactor.callWhenRunning(lambda: d.callback(True))
+            # type-ignore: This is outside of Synapse (just a utility benchmark script)
+            # so we don't need to worry about  which server the logs are coming from
+            # (`Clock.call_when_running` manages the logcontext for us).
+            reactor.callWhenRunning(lambda: d.callback(True))  # type: ignore[prefer-synapse-clock-call-when-running]
             reactor.run()
 
         # mypy thinks this is an object for some reason.

From 731f36e131a1f1328f11ecd7899e8bf22ac8bfac Mon Sep 17 00:00:00 2001
From: Eric Eastwood <erice@element.io>
Date: Fri, 19 Sep 2025 14:59:12 -0500
Subject: [PATCH 06/12] Remove manual `LoggingContext`

---
 synapse/_scripts/synapse_port_db.py |  3 +--
 synapse/app/generic_worker.py       |  4 +---
 synapse/app/homeserver.py           | 16 +++++++---------
 3 files changed, 9 insertions(+), 14 deletions(-)

diff --git a/synapse/_scripts/synapse_port_db.py b/synapse/_scripts/synapse_port_db.py
index 211ed2e8638..fd846489771 100755
--- a/synapse/_scripts/synapse_port_db.py
+++ b/synapse/_scripts/synapse_port_db.py
@@ -1586,8 +1586,7 @@ def start(stdscr: Optional["curses.window"] = None) -> None:
 
         @defer.inlineCallbacks
         def run() -> Generator["defer.Deferred[Any]", Any, None]:
-            with LoggingContext("synapse_port_db_run"):
-                yield defer.ensureDeferred(porter.run())
+            yield defer.ensureDeferred(porter.run())
 
         hs.get_clock().call_when_running(run)
 
diff --git a/synapse/app/generic_worker.py b/synapse/app/generic_worker.py
index 4563690b6dd..0849f25059c 100644
--- a/synapse/app/generic_worker.py
+++ b/synapse/app/generic_worker.py
@@ -356,9 +356,7 @@ def start(config_options: List[str]) -> None:
         handle_startup_exception(e)
 
     async def start() -> None:
-        # Re-establish log context now that we're back from the reactor
-        with LoggingContext("start"):
-            await _base.start(hs)
+        await _base.start(hs)
 
     register_start(hs, start)
 
diff --git a/synapse/app/homeserver.py b/synapse/app/homeserver.py
index 3dffe6166b6..54c41c0c285 100644
--- a/synapse/app/homeserver.py
+++ b/synapse/app/homeserver.py
@@ -377,17 +377,15 @@ def setup(config_options: List[str]) -> SynapseHomeServer:
         handle_startup_exception(e)
 
     async def start() -> None:
-        # Re-establish log context now that we're back from the reactor
-        with LoggingContext("start"):
-            # Load the OIDC provider metadatas, if OIDC is enabled.
-            if hs.config.oidc.oidc_enabled:
-                oidc = hs.get_oidc_handler()
-                # Loading the provider metadata also ensures the provider config is valid.
-                await oidc.load_metadata()
+        # Load the OIDC provider metadatas, if OIDC is enabled.
+        if hs.config.oidc.oidc_enabled:
+            oidc = hs.get_oidc_handler()
+            # Loading the provider metadata also ensures the provider config is valid.
+            await oidc.load_metadata()
 
-            await _base.start(hs)
+        await _base.start(hs)
 
-            hs.get_datastores().main.db_pool.updates.start_doing_background_updates()
+        hs.get_datastores().main.db_pool.updates.start_doing_background_updates()
 
     register_start(hs, start)
 

From 0f8076ab41964ea886c21a05f0847e5f1553d423 Mon Sep 17 00:00:00 2001
From: Eric Eastwood <erice@element.io>
Date: Fri, 19 Sep 2025 15:00:30 -0500
Subject: [PATCH 07/12] Fix copy-paste typos

---
 synapse/util/clock.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/synapse/util/clock.py b/synapse/util/clock.py
index 6a72197d2a0..c9b786f7b62 100644
--- a/synapse/util/clock.py
+++ b/synapse/util/clock.py
@@ -172,7 +172,7 @@ def call_when_running(
 
         def wrapped_callback(*args: Any, **kwargs: Any) -> None:
             assert context.current_context() is context.SENTINEL_CONTEXT, (
-                "Expected `call_later` callback from the reactor to start with the sentinel logcontext "
+                "Expected `call_when_running` callback from the reactor to start with the sentinel logcontext "
                 f"but saw {context.current_context()}. In other words, another task shouldn't have "
                 "leaked their logcontext to us."
             )
@@ -181,7 +181,7 @@ def wrapped_callback(*args: Any, **kwargs: Any) -> None:
             # `sentinel` log context at this point. We want the function to log with
             # some logcontext as we want to know which server the logs came from.
             #
-            # We use `PreserveLoggingContext` to prevent our new `call_later`
+            # We use `PreserveLoggingContext` to prevent our new `call_when_running`
             # logcontext from finishing as soon as we exit this function, in case `f`
             # returns an awaitable/deferred which would continue running and may try to
             # restore the `loop_call` context when it's done (because it's trying to

From 6938134f7d6de2cdedbb395d13f6652931603cbb Mon Sep 17 00:00:00 2001
From: Eric Eastwood <erice@element.io>
Date: Fri, 19 Sep 2025 15:05:44 -0500
Subject: [PATCH 08/12] We can't assume sentinel context when callback is
 called

---
 synapse/util/clock.py | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/synapse/util/clock.py b/synapse/util/clock.py
index c9b786f7b62..8d6ab007ba1 100644
--- a/synapse/util/clock.py
+++ b/synapse/util/clock.py
@@ -171,11 +171,15 @@ def call_when_running(
         """
 
         def wrapped_callback(*args: Any, **kwargs: Any) -> None:
-            assert context.current_context() is context.SENTINEL_CONTEXT, (
-                "Expected `call_when_running` callback from the reactor to start with the sentinel logcontext "
-                f"but saw {context.current_context()}. In other words, another task shouldn't have "
-                "leaked their logcontext to us."
-            )
+            # Since this callback can be invoked immediately if the reactor is already
+            # running, we can't always assume that we're running in the sentinel
+            # logcontext (i.e. we can't assert that we're in the sentinel context like
+            # we can in other methods).
+            #
+            # We will only be running in the sentinel logcontext if the reactor was not
+            # running when `call_when_running` was invoked and later starts up.
+            #
+            # assert context.current_context() is context.SENTINEL_CONTEXT
 
             # Because this is a callback from the reactor, we will be using the
             # `sentinel` log context at this point. We want the function to log with

From 7b83c9fcbcc7eefd79f6556dfd3d1e8128bb6e87 Mon Sep 17 00:00:00 2001
From: Eric Eastwood <erice@element.io>
Date: Fri, 19 Sep 2025 15:11:58 -0500
Subject: [PATCH 09/12] Add changelog

---
 changelog.d/18944.misc | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 changelog.d/18944.misc

diff --git a/changelog.d/18944.misc b/changelog.d/18944.misc
new file mode 100644
index 00000000000..a7a09630c22
--- /dev/null
+++ b/changelog.d/18944.misc
@@ -0,0 +1 @@
+Introduce `Clock.call_when_running(...)` so that any Synapse code running when the reactor starts includes logcontext as we want to know which server the logs came from.

From 62f93ded1f8dbc35864d5beeb295427fa1c1cf2b Mon Sep 17 00:00:00 2001
From: Eric Eastwood <erice@element.io>
Date: Fri, 19 Sep 2025 15:13:46 -0500
Subject: [PATCH 10/12] Better changelog

---
 changelog.d/18944.misc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/changelog.d/18944.misc b/changelog.d/18944.misc
index a7a09630c22..9561aa92753 100644
--- a/changelog.d/18944.misc
+++ b/changelog.d/18944.misc
@@ -1 +1 @@
-Introduce `Clock.call_when_running(...)` so that any Synapse code running when the reactor starts includes logcontext as we want to know which server the logs came from.
+Introduce `Clock.call_when_running(...)` to wrap startup code in a logcontext, ensuring we can identify which server generated the logs.

From 19a4f8c741836078def0c011aa61e4580cb5fd63 Mon Sep 17 00:00:00 2001
From: Eric Eastwood <erice@element.io>
Date: Fri, 19 Sep 2025 15:20:20 -0500
Subject: [PATCH 11/12] Fix lints

---
 synapse/_scripts/synapse_port_db.py | 1 -
 1 file changed, 1 deletion(-)

diff --git a/synapse/_scripts/synapse_port_db.py b/synapse/_scripts/synapse_port_db.py
index fd846489771..f2d75d4ff70 100755
--- a/synapse/_scripts/synapse_port_db.py
+++ b/synapse/_scripts/synapse_port_db.py
@@ -54,7 +54,6 @@
 from synapse.config.database import DatabaseConnectionConfig
 from synapse.config.homeserver import HomeServerConfig
 from synapse.logging.context import (
-    LoggingContext,
     make_deferred_yieldable,
     run_in_background,
 )

From 4a9730ee763719c2f8e3953735a18f8308ceb522 Mon Sep 17 00:00:00 2001
From: Eric Eastwood <erice@element.io>
Date: Fri, 19 Sep 2025 15:36:42 -0500
Subject: [PATCH 12/12] Fix wrong config typo

---
 synapse/_scripts/synapse_port_db.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/synapse/_scripts/synapse_port_db.py b/synapse/_scripts/synapse_port_db.py
index f2d75d4ff70..b0a067edcbc 100755
--- a/synapse/_scripts/synapse_port_db.py
+++ b/synapse/_scripts/synapse_port_db.py
@@ -1567,7 +1567,7 @@ def main() -> None:
     config = HomeServerConfig()
     config.parse_config_dict(hs_config, "", "")
 
-    hs = MockHomeserver(hs_config)
+    hs = MockHomeserver(config)
 
     def start(stdscr: Optional["curses.window"] = None) -> None:
         progress: Progress