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fix(gateway): bound lifespan shutdown hooks to prevent worker hang under uvicorn reload (#2331)

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* fix(gateway): bound lifespan shutdown hooks to prevent worker hang

Gateway worker can hang indefinitely in `uvicorn --reload` mode with
the listening socket still bound — all /api/* requests return 504,
and SIGKILL is the only recovery.

Root cause (py-spy dump from a reproduction showed 16+ stacked frames
of signal_handler -> Event.set -> threading.Lock.__enter__ on the
main thread): CPython's `threading.Event` uses `Condition(Lock())`
where the inner Lock is non-reentrant. uvicorn's BaseReload signal
handler calls `should_exit.set()` directly from signal context; if a
second signal (SIGTERM/SIGHUP from the reload supervisor, or
watchfiles-triggered reload) arrives while the first handler holds
the Lock, the reentrant call deadlocks on itself.

The reload supervisor keeps sending those signals only when the
worker fails to exit promptly. DeerFlow's lifespan currently awaits
`stop_channel_service()` with no timeout; if a channel's `stop()`
stalls (e.g. Feishu/Slack WebSocket waiting for an ack), the worker
can't exit, the supervisor keeps signaling, and the deadlock becomes
reachable.

This is a defense-in-depth fix — it does not repair the upstream
uvicorn/CPython issue, but it ensures DeerFlow's lifespan exits
within a bounded window so the supervisor has no reason to keep
firing signals. No behavior change on the happy path.

Wraps the shutdown hook in `asyncio.wait_for(timeout=5.0)` and logs
a warning on timeout before proceeding to worker exit.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* Update backend/app/gateway/app.py

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* style: apply make format (ruff) to test assertions

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Co-authored-by: Willem Jiang <willem.jiang@gmail.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
This commit is contained in:
JerryChaox
2026-04-23 19:41:26 +08:00
committed by GitHub
parent c42ae3af79
commit 4e72410154
2 changed files with 84 additions and 2 deletions
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backend/app/gateway/app.py
+16 -2
View File
@@ -1,3 +1,4 @@
import asyncio
import logging
from collections.abc import AsyncGenerator
from contextlib import asynccontextmanager
@@ -32,6 +33,11 @@ logging.basicConfig(
logger = logging.getLogger(__name__)
# Upper bound (seconds) each lifespan shutdown hook is allowed to run.
# Bounds worker exit time so uvicorn's reload supervisor does not keep
# firing signals into a worker that is stuck waiting for shutdown cleanup.
_SHUTDOWN_HOOK_TIMEOUT_SECONDS = 5.0
@asynccontextmanager
async def lifespan(app: FastAPI) -> AsyncGenerator[None, None]:
@@ -63,11 +69,19 @@ async def lifespan(app: FastAPI) -> AsyncGenerator[None, None]:
yield
# Stop channel service on shutdown
# Stop channel service on shutdown (bounded to prevent worker hang)
try:
from app.channels.service import stop_channel_service
await stop_channel_service()
await asyncio.wait_for(
stop_channel_service(),
timeout=_SHUTDOWN_HOOK_TIMEOUT_SECONDS,
)
except TimeoutError:
logger.warning(
"Channel service shutdown exceeded %.1fs; proceeding with worker exit.",
_SHUTDOWN_HOOK_TIMEOUT_SECONDS,
)
except Exception:
logger.exception("Failed to stop channel service")