Support `Event.wait(timeout=...)` and `Event.clear()` #8

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Merged

patrick-kidger merged 9 commits into tweaks from timeout

Aug 2, 2025

README.md

-Original file line number
+Diff line change
@@ -1,5 +1,5 @@
     <h1 align="center">tinyio</h1>
-    <h2 align="center">A tiny (~200 lines) event loop for Python</h2>
+    <h2 align="center">A tiny (~300 lines) event loop for Python</h2>
     _Ever used `asyncio` and wished you hadn't?_
@@ Expand Down Expand Up / @@ -137,7 +137,13 @@ tinyio.Lock @@
     - `tinyio.Event()`
-        This has a method `.wait()`, which is a coroutine you can `yield` on. This will unblock once its `.set()` method is called (typically from another coroutine). It also has a `is_set()` method for checking whether it has been set.
+        This is a wrapper around a boolean flag, initialised with `False`.
+        This has the following methods:
+        - `.is_set()`: check the value of the flag.
+        - `.set()`: set the flag to `True`.
+        - `.clear()`: set the flag to `False`.
+        - `.wait()`, which is a coroutine you can `yield` on. This will unblock if the internal flag is `True`. (Typically this is accomplished by calling `.set()` from another coroutine or from a thread.)
     ---
@@ Expand Down @@

tests/test_basic.py → tests/test_core.py

-Original file line number
+Diff line change
@@ -1,5 +1,7 @@
     import gc
+    import threading
     import time
+    from typing import Any
     import pytest
     import tinyio
@@ Expand Down Expand Up / @@ -276,3 +278,164 @@ def _gc(x: int) -> tinyio.Coro[tuple[int, int]]: @@
         assert loop.run(coro) == (5, 5)
         gc.collect()
         assert set(loop._results.keys()) == {coro}
+    def test_event_fairness():
+        """This checks that once one event unblocks, that we don't just keep chasing all the stuff downstream of that event,
+        i.e. that we do schedule work from any other event that has finished.
+        """
+        outs = []
+        def f():
+            yield tinyio.Event().wait(0)
+            outs.append(1)
+            for _ in range(20):
+                yield
+            outs.append(2)
+        def g():
+            yield [f(), f()]
+        loop = tinyio.Loop()
+        loop.run(g())
+        assert outs == [1, 1, 2, 2]
+    def test_event_fairness2():
+        event1 = tinyio.Event()
+        outs = []
+        def f():
+            yield event1.wait(0)
+            outs.append(1)
+        def g():
+            yield {f()}
+            for _ in range(20):
+                yield
+            outs.append(2)
+        loop = tinyio.Loop()
+        loop.run(g())
+        assert outs == [1, 2]
+    def test_simultaneous_set():
+        event = tinyio.Event()
+        def f():
+            for _ in range(20):
+                yield
+            yield [tinyio.run_in_thread(event.set) for _ in range(100)]
+        def g():
+            yield event.wait()
+        def h():
+            yield [g(), f()]
+        loop = tinyio.Loop()
+        loop.run(h())
+    def test_timeout_then_set():
+        event1 = tinyio.Event()
+        event2 = tinyio.Event()
+        def f():
+            yield [event1.wait(0), event2.wait()]
+        def g():
+            yield {f()}
+            for _ in range(20):
+                yield
+            event1.set()
+            for _ in range(20):
+                yield
+            event2.set()
+            return 3
+        loop = tinyio.Loop()
+        assert loop.run(g()) == 3
+    def test_set_then_timeout():
+        event1 = tinyio.Event()
+        event2 = tinyio.Event()
+        def f():
+            event1.set()
+            yield [event1.wait(0), event2.wait()]
+        def g():
+            yield {f()}
+            for _ in range(20):
+                yield
+            event2.set()
+            return 3
+        loop = tinyio.Loop()
+        assert loop.run(g()) == 3
+    def test_set_then_timeout_then_clear():
+        event1 = tinyio.Event()
+        event2 = tinyio.Event()
+        def f():
+            event1.set()
+            yield [event1.wait(0), event2.wait()]
+        def g():
+            yield {f()}
+            for _ in range(20):
+                yield
+            event1.clear()
+            event2.set()
+            return 3
+        loop = tinyio.Loop()
+        assert loop.run(g()) == 3
+    def test_set_then_timeout_then_clear_then_set():
+        event1 = tinyio.Event()
+        event2 = tinyio.Event()
+        def f():
+            event1.set()
+            yield [event1.wait(0), event2.wait()]
+        def g():
+            yield {f()}
+            for _ in range(20):
+                yield
+            event1.clear()
+            event2.set()
+            event1.set()
+            return 3
+        loop = tinyio.Loop()
+        assert loop.run(g()) == 3
+    def test_timeout_as_part_of_group_and_only_coroutine():
+        event1 = tinyio.Event()
+        event2 = tinyio.Event()
+        wait: Any = event1.wait(0)
+        wait2 = event2.wait()
+        def f():
+            yield [wait, wait2]
+            return 3
+        def set2():
+            while wait.state != tinyio._core._WaitState.NOTIFIED_TIMEOUT:
+                pass
+            time.sleep(0.1)
+            event2.set()
+        t = threading.Thread(target=set2)
+        t.start()
+        loop = tinyio.Loop()
+        assert loop.run(f()) == 3

tests/test_sync.py

-Original file line number
+Diff line change
@@ Expand Up / @@ -152,7 +152,7 @@ def test_event_run(is_set: bool): @@
     @pytest.mark.parametrize("is_set", (False, True))
-    def test_event_double_wait(is_set: bool):
+    def test_event_repeated_wait(is_set: bool):
         event = tinyio.Event()
         if is_set:
             event.set()
@@ Expand Down Expand Up / @@ -184,3 +184,103 @@ def _foo(): @@
         loop = tinyio.Loop()
         loop.run(_foo())
+    @pytest.mark.parametrize("is_set", (False, True))
+    def test_event_simultaneous_repeated_wait(is_set: bool):
+        event = tinyio.Event()
+        if is_set:
+            event.set()
+        def foo():
+            wait = event.wait()
+            if not is_set:
+                t = threading.Timer(0.1, lambda: event.set())
+                t.start()
+            yield [wait, wait]
+        loop = tinyio.Loop()
+        with pytest.raises(RuntimeError, match=re.escape("Do not yield the same `event.wait()` multiple times")):
+            loop.run(foo())
+    def test_event_clear_not_strict():
+        event = tinyio.Event()
+        event.set()
+        event.clear()
+        assert not event.is_set()
+        out = []
+        def foo():
+            yield event.wait()
+            out.append(2)
+        def bar():
+            yield
+            out.append(1)
+            event.set()
+            yield
+            # Even though we `clear()` the event again afterwards, both `foo()` still unblock.
+            event.clear()
+            out.append(3)
+        def baz():
+            yield [foo(), foo(), bar()]
+        loop = tinyio.Loop()
+        loop.run(baz())
+        assert out == [1, 2, 2, 3]
+    class _Semaphore:
+        def __init__(self, value):
+            self.value = value
+            self.event = tinyio.Event()
+            self.event.set()
+        def __call__(self):
+            while True:
+                yield self.event.wait()
+                if self.event.is_set():
+                    break
+            assert self.value > 0
+            self.value -= 1
+            if self.value == 0:
+                self.event.clear()
+            return _closing(self)
+    @contextlib.contextmanager
+    def _closing(semaphore):
+        try:
+            yield
+        finally:
+            semaphore.value += 1
+            semaphore.event.set()
+    def test_alternate_semaphore():
+        """This test is useful as it makes use of `Event.clear()`."""
+        counter = 0
+        def _count(semaphore, i):
+            nonlocal counter
+            with (yield semaphore()):
+                counter += 1
+                if counter > 2:
+                    raise RuntimeError
+                yield
+                counter -= 1
+            return i
+        def _run(value):
+            semaphore = _Semaphore(value)
+            out = yield [_count(semaphore, i) for i in range(50)]
+            return out
+        loop = tinyio.Loop()
+        assert loop.run(_run(2)) == list(range(50))
+        with pytest.raises(RuntimeError):
+            loop.run(_run(3))

tests/test_time.py

-Original file line number
+Diff line change
@@ -1,6 +1,27 @@
+    import time
     import tinyio
+    def test_sleep():
+        outs = []
+        def f():
+            start = time.monotonic()
+            yield [tinyio.sleep(0.05), tinyio.sleep(0.1)]
+            actual_duration = time.monotonic() - start
+            # Note that these are pretty inaccurate tolerances! This is about what we get with `asyncio` too.
+            # The reason for this seems to be the accuracy in the `threading.Event.wait()` that we bottom out in. If we need
+            # greater resolution than this then we could do that by using a busy-loop for the last 1e-2 seconds.
+            success = 0.09 < actual_duration < 0.11
+            outs.append(success)
+        loop = tinyio.Loop()
+        for _ in range(5):
+            loop.run(f())
+        assert sum(outs) >= 4  # We allow one failure, to decrease flakiness.
     def _sleep(x):
         yield tinyio.sleep(x)
         return 3
@@ Expand Down @@

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