Update 2025-04-13_16:26:04

venv/lib/python3.11/site-packages/fastapi/concurrency.py

@@ -0,0 +1,39 @@
+from contextlib import asynccontextmanager as asynccontextmanager
+from typing import AsyncGenerator, ContextManager, TypeVar
+
+import anyio.to_thread
+from anyio import CapacityLimiter
+from starlette.concurrency import iterate_in_threadpool as iterate_in_threadpool  # noqa
+from starlette.concurrency import run_in_threadpool as run_in_threadpool  # noqa
+from starlette.concurrency import (  # noqa
+    run_until_first_complete as run_until_first_complete,
+)
+
+_T = TypeVar("_T")
+
+
+@asynccontextmanager
+async def contextmanager_in_threadpool(
+    cm: ContextManager[_T],
+) -> AsyncGenerator[_T, None]:
+    # blocking __exit__ from running waiting on a free thread
+    # can create race conditions/deadlocks if the context manager itself
+    # has its own internal pool (e.g. a database connection pool)
+    # to avoid this we let __exit__ run without a capacity limit
+    # since we're creating a new limiter for each call, any non-zero limit
+    # works (1 is arbitrary)
+    exit_limiter = CapacityLimiter(1)
+    try:
+        yield await run_in_threadpool(cm.__enter__)
+    except Exception as e:
+        ok = bool(
+            await anyio.to_thread.run_sync(
+                cm.__exit__, type(e), e, e.__traceback__, limiter=exit_limiter
+            )
+        )
+        if not ok:
+            raise e
+    else:
+        await anyio.to_thread.run_sync(
+            cm.__exit__, None, None, None, limiter=exit_limiter
+        )