uvicorn Shutdown process is broken in 0.15 (Fix)

The Fix

Upgrade to version 0.16.0 or later.

Based on closed Kludex/uvicorn issue #1160 · PR/commit linked

Production note: Most teams hit this during upgrades or environment changes. Roll out with a canary and smoke critical endpoints (health, OpenAPI/docs) before 100%.

Jump to Verify Open PR/Commit

@@ -310,7 +310,7 @@ def install_signal_handlers(self) -> None:
     def handle_exit(self, sig: signal.Signals, frame: FrameType) -> None:
 
-        if self.should_exit:
+        if self.should_exit and sig == signal.SIGINT:
             self.force_exit = True

repro.py

async def _lifespan(app):
  import asyncio
  try:
    yield
  except asyncio.exceptions.CancelledError:
    pass
server_app = Starlette(routes=routes, lifespan=_lifespan)

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

fix.md

Option A — Upgrade to fixed release\nUpgrade to version 0.16.0 or later.\nWhen NOT to use: Do not apply this fix if your application relies on the previous shutdown behavior.\n\n

Why This Fix Works in Production

Trigger: [2021-08-19 11:01:19,614][25024] INFO: Uvicorn running on http://0.0.0.0:5000 (Press CTRL+C to quit)
Mechanism: The shutdown process fails due to improper handling of SIGINT signals in the server's exit logic
Why the fix works: Fixes the shutdown process issue in Uvicorn by ensuring that the server can gracefully handle SIGINT signals. (first fixed release: 0.16.0).

Production impact:

If left unfixed, the same config can fail only in production (env differences), causing startup failures or partial feature outages.

Why This Breaks in Prod

Triggered by an upgrade/regression window: 0.15 breaks; 0.16.0 is the first fixed release.
Shows up under Python 3.8 in real deployments (not just unit tests).
The shutdown process fails due to improper handling of SIGINT signals in the server's exit logic
Surfaces as: [2021-08-19 11:01:19,614][25024] INFO: Uvicorn running on http://0.0.0.0:5000 (Press CTRL+C to quit)

Proof / Evidence

GitHub issue: #1160
Fix PR: https://github.com/kludex/uvicorn/pull/1269
First fixed release: 0.16.0
Affected versions: 0.15
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.75
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.31

Discussion

High-signal excerpts from the issue thread (symptoms, repros, edge-cases).

Jump to Sources Open on GitHub

“I'm having the exactly same issue!! Here's the code https://github.com/igormcsouza/kitty-api/blob/master/api/__init__.py I downgrade to 0.14 just to avoid error”

@igormcsouza · 2021-10-12 · source

“When I press CTRL + C it sends two signals to handle_exit(), first a SIGNIT followed by a SIGTERM. I'm debugging it.”

@Kludex · 2021-08-19 · source

“Ok... It was quite fast to find it :sweat_smile: The problem is that on reload mode, we terminate the process on the shutdown(): https://github.com/encode/uvicorn/commit/de53c2366f1df9f55ac88d8bde67cfd314d2d98e”

@Kludex · 2021-08-19 · source

“> Ok... It was quite fast to find it > > The problem is that on reload mode, we terminate the process on the shutdown():…”

@euri10 · 2021-08-19 · source

Failure Signature (Search String)

[2021-08-19 11:01:19,614][25024] INFO: Uvicorn running on http://0.0.0.0:5000 (Press CTRL+C to quit)

Error Message

Stack trace

error.txt

Error Message
-------------
[2021-08-19 11:01:19,614][25024] INFO:     Uvicorn running on http://0.0.0.0:5000 (Press CTRL+C to quit)
[2021-08-19 11:01:23,189][25024] ERROR:    Traceback (most recent call last):
  File "c:\Users\...\.venv\lib\site-packages\starlette\routing.py", line 624, in lifespan
    await receive()
  File "c:\Users\...\.venv\lib\site-packages\uvicorn\lifespan\on.py", line 135, in receive
    return await self.receive_queue.get()
  File "C:\Users\...\python\current\lib\asyncio\queues.py", line 166, in get
    await getter
asyncio.exceptions.CancelledError

Stack trace

error.txt

Error Message
-------------
0:00:00.901396  INFO       13 show_systeminfo  Processor: Intel64 Family 6 Model 165 Stepping 2, GenuineIntel
0:00:00.902397  INFO       14 show_systeminfo  Machine  : AMD64
0:00:00.903399  INFO       15 show_systeminfo  Node     : DESKTOP-VF4OT9Q
0:00:00.904396  INFO       16 show_systeminfo  System   : Windows
0:00:00.910397  INFO       17 show_systeminfo  Platform : Windows-10-10.0.19044-SP0
0:00:00.911397  INFO       26 startup_event    Starting: Tasks
INFO:     Application startup complete.
INFO:     Uvicorn running on http://127.0.0.1:53259 (Press CTRL+C to quit)
INFO:     Shutting down
INFO:     Finished server process [15628]
0:00:01.801396  INFO       30 shutdown_event   Shutting down...
0:00:01.802398  INFO       32 shutdown_event   Shutting down: Tasks
ERROR:    Traceback (most recent call last):
  File "C:\Users\darko\AppData\Local\Temp\ONC4D5~1\starlette\routing.py", line 624, in lifespan
  File "C:\Users\darko\AppData\Local\Temp\ONC4D5~1\uvicorn\lifespan\on.py", line 135, in receive
  File "C:\Users\darko\AppData\Local\Temp\ONC4D5~1\asyncio\queues.py", line 166, in get
asyncio.exceptions.CancelledError

Stack trace

error.txt

Error Message
-------------
INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
INFO:     Started parent process [10954]
INFO:     Started server process [10958]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Started server process [10959]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Started server process [10961]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Started server process [10960]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
^CINFO:     Shutting down
INFO:     Shutting down
INFO:     Shutting down
INFO:     Shutting down
INFO:     Waiting for application shutdown.
INFO:     Application shutdown complete.
INFO:     Finished server process [10959]
INFO:     Waiting for application shutdown.
INFO:     Application shutdown complete.
INFO:     Finished server process [10961]
INFO:     Waiting for application shutdown.
INFO:     Application shutdown complete.
INFO:     Finished server process [10960]
INFO:     Finished server process [10958]
ERROR:    Traceback (most recent call last):
  File "/home/user/code/project/.venv/lib/python3.8/site-packages/starlette/routing.py", line 638, in lifespan
    await receive()
  File "/home/user/code/project/.venv/lib/python3.8/site-packages/uvicorn/lifespan/on.py", l
... (truncated) ...

Minimal Reproduction

repro.py

async def _lifespan(app):
  import asyncio
  try:
    yield
  except asyncio.exceptions.CancelledError:
    pass
server_app = Starlette(routes=routes, lifespan=_lifespan)

Environment

Python: 3.8

What Broke

The server does not shut down gracefully, leading to potential data loss and unhandled exceptions.

Why It Broke

The shutdown process fails due to improper handling of SIGINT signals in the server's exit logic

Fix Options (Details)

Option A — Upgrade to fixed release Safe default (recommended)

Upgrade to version 0.16.0 or later.

When NOT to use: Do not apply this fix if your application relies on the previous shutdown behavior.

Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.

Option D — Guard side-effects with OnceOnly Guardrail for side-effects

Mitigate duplicate external side-effects under retries/timeouts/agent loops by gating the operation before calling external systems.

Place OnceOnly between your code/agent and real side-effects (Stripe, emails, CRM, APIs).
Use a stable key per side-effect (e.g., customer_id + action + idempotency_key).
Fail-safe: configure fail-open vs fail-closed based on blast radius and spend risk.

Show example snippet (optional)

onceonly.py

from onceonly import OnceOnly
import os

once = OnceOnly(api_key=os.environ["ONCEONLY_API_KEY"], fail_open=True)

# Stable idempotency key per real side-effect.
# Use a request id / job id / webhook delivery id / Stripe event id, etc.
event_id = "evt_..."  # replace
key = f"stripe:webhook:{event_id}"

res = once.check_lock(key=key, ttl=3600)
if res.duplicate:
    return {"status": "already_processed"}

# Safe to execute the side-effect exactly once.
handle_event(event_id)

See OnceOnly SDK

When NOT to use: Do not use this to hide logic bugs or data corruption. Use it to block duplicate external side-effects and enforce tool permissions/spend caps.

Fix reference: https://github.com/kludex/uvicorn/pull/1269

First fixed release: 0.16.0

Last verified: 2026-02-09. Validate in your environment.

When NOT to Use This Fix

Do not apply this fix if your application relies on the previous shutdown behavior.
Do not use this to hide logic bugs or data corruption. Use it to block duplicate external side-effects and enforce tool permissions/spend caps.

Verify Fix

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

Did This Fix Work in Your Case?

Quick signal helps us prioritize which fixes to verify and improve.

Prevention

Add a stress test that runs high-concurrency workloads and fails on thread dumps / blocked locks.
Enable watchdog dumps in prod (faulthandler, thread dump endpoint) to capture deadlocks quickly.
Make timeouts explicit and test them (unit + integration) to avoid silent behavior changes.
Instrument retries (attempt count + reason) and alert on spikes to catch dependency slowdowns.

Version Compatibility Table

Version	Status
0.15	Broken
0.16.0	Fixed

Related Issues

No related fixes found.

Cluster: uvicorn:configuration-error All hubs All clusters

Related clusters: Data consistency Race condition SSL handshake

Sources

We don’t republish the full GitHub discussion text. Use the links above for context.

uvicorn Shutdown process is broken in 0.15 (Fix)

The Fix

Why This Fix Works in Production

Why This Breaks in Prod

Proof / Evidence

Discussion

Failure Signature (Search String)

Error Message

Minimal Reproduction

Environment

What Broke

Why It Broke

Fix Options (Details)

Option A — Upgrade to fixed release Safe default (recommended)

Option D — Guard side-effects with OnceOnly Guardrail for side-effects

Get updates

When NOT to Use This Fix

Verify Fix

Did This Fix Work in Your Case?

Prevention

Version Compatibility Table

Related Issues

Sources