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Flush the stdout buffer on Windows to trigger reload #2604

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Merged
merged 5 commits into from
Apr 14, 2025
Merged

Flush the stdout buffer on Windows to trigger reload #2604

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657f0f0
Improve reloading on Windows
jamesh1999 Mar 28, 2025
ba87386
Fix lint
jamesh1999 Mar 28, 2025
716446b
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jamesh1999 Apr 13, 2025
e34ab31
Fix lint
jamesh1999 Apr 13, 2025
94a80d2
Merge branch 'master' into bugfix/reload-hangs-on-windows
Kludex Apr 14, 2025
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1 change: 1 addition & 0 deletions uvicorn/supervisors/basereload.py
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Expand Up @@ -90,6 +90,7 @@ def restart(self) -> None:
self.is_restarting = True
assert self.process.pid is not None
os.kill(self.process.pid, signal.CTRL_C_EVENT)
print("") # This helps trigger windows to respond to the Ctrl+C event
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Can you try to use sys.stdout.flush() instead?

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So I did give this a go before and sys.stdout.flush() on its own doesn't seem to be enough. Based on Copilot's review, I also tried the following:

  • sys.stdout.write("") then sys.stdout.flush() - No success here, it still doesn't trigger a reload.
  • sys.stdout.write("\n") then sys.stdout.flush() - This is closer to print("") and does work. But at that point, I'm not sure it's any better than just using print("")

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Looks like sys.stdout.write(" ") then sys.stdout.flush() works too actually. That's a little less intrusive to the logs than printing a blank line and possibly a little bit clearer at showing what's required to get a reload to happen (something needs to be printed & the buffer need to be flushed)

else: # pragma: py-win32
self.process.terminate()
self.process.join()
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