fix(chat): handle message creation in own thread

backend/onyx/server/query_and_chat/chat_backend.py

@@ -1,6 +1,8 @@
+import asyncio
 import datetime
 import json
 import os
+from collections.abc import AsyncGenerator
 from collections.abc import Generator
 from datetime import timedelta
 from uuid import UUID
@@ -103,6 +105,7 @@
 from onyx.utils.headers import get_custom_tool_additional_request_headers
 from onyx.utils.logger import setup_logger
 from onyx.utils.telemetry import mt_cloud_telemetry
+from onyx.utils.threadpool_concurrency import run_in_background
 from shared_configs.contextvars import get_current_tenant_id
 
 logger = setup_logger()
@@ -507,7 +510,7 @@ def stream_generator() -> Generator[str, None, None]:
 
 
 @router.post("/send-chat-message", response_model=None, tags=PUBLIC_API_TAGS)
-def handle_send_chat_message(
+async def handle_send_chat_message(
     chat_message_req: SendMessageRequest,
     request: Request,
     user: User | None = Depends(current_chat_accessible_user),
@@ -572,34 +575,63 @@ def handle_send_chat_message(
             # Note: LLM cost tracking is now handled in multi_llm.py
             return result
 
-    # Streaming path, normal Onyx UI behavior
-    def stream_generator() -> Generator[str, None, None]:
+    # Use prod-cons pattern to continue processing even if request stops yielding
+    buffer: asyncio.Queue[str | None] = asyncio.Queue()
+    loop = asyncio.get_running_loop()
+
+    # Capture headers before spawning thread
+    litellm_headers = extract_headers(request.headers, LITELLM_PASS_THROUGH_HEADERS)
+    custom_tool_headers = get_custom_tool_additional_request_headers(request.headers)
+
+    def producer() -> None:
+        """
+        Producer function that runs handle_stream_message_objects in a loop
+        and writes results to the buffer.
+        """
         state_container = ChatStateContainer()
         try:
+            logger.debug("Producer started")
             with get_session_with_current_tenant() as db_session:
                 for obj in handle_stream_message_objects(
                     new_msg_req=chat_message_req,
                     user=user,
                     db_session=db_session,
-                    litellm_additional_headers=extract_headers(
-                        request.headers, LITELLM_PASS_THROUGH_HEADERS
-                    ),
-                    custom_tool_additional_headers=get_custom_tool_additional_request_headers(
-                        request.headers
-                    ),
+                    litellm_additional_headers=litellm_headers,
+                    custom_tool_additional_headers=custom_tool_headers,
                     external_state_container=state_container,
                 ):
-                    yield get_json_line(obj.model_dump())
+                    # Thread-safe put into the asyncio queue
+                    loop.call_soon_threadsafe(
+                        buffer.put_nowait, get_json_line(obj.model_dump())
+                    )
                 # Note: LLM cost tracking is now handled in multi_llm.py
-
         except Exception as e:
             logger.exception("Error in chat message streaming")
-            yield json.dumps({"error": str(e)})
-
+            loop.call_soon_threadsafe(buffer.put_nowait, json.dumps({"error": str(e)}))
         finally:
-            logger.debug("Stream generator finished")
+            # Signal end of stream
+            loop.call_soon_threadsafe(buffer.put_nowait, None)
+            logger.debug("Producer finished")
+
+    async def stream_from_buffer() -> AsyncGenerator[str, None]:
+        """
+        Async generator that reads from the buffer and yields to the client.
+        """
+        try:
+            while True:
+                item = await buffer.get()
+                if item is None:
+                    # End of stream signal
+                    break
+                yield item
+        except asyncio.CancelledError:
+            logger.warning("Stream cancelled (Consumer disconnected)")
+        finally:
+            logger.debug("Stream consumer finished")
 
-    return StreamingResponse(stream_generator(), media_type="text/event-stream")
+    run_in_background(producer)
+
+    return StreamingResponse(stream_from_buffer(), media_type="text/event-stream")
 
 
 @router.put("/set-message-as-latest")