concurrency.py•1.42 kB
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
)