Slow reload on Windows 10 using PyCharm

[Kludex]

Discussed in #1977

^{Originally posted by adhihargo May 14, 2023}
Uvicorn used to work fine in my dev laptop running Windows 10, but now every time there's a modified change, it stuck in this line:

WARNING: WatchFiles detected changes in 'main.py'. Reloading...

... for nearly 5 minutes before actually reloading the files (printing Shutting down in the next line, etc.). During that time, the API server part works normally but serving the older version before file modification..

Downgraded to v0.21.1, and reloading works instantly again.

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[3to1null]

I think issue lies somewhere here:

uvicorn/uvicorn/supervisors/basereload.py

Lines 87 to 99 in 7d4eab2

	def restart(self) -> None:
	if sys.platform == "win32": # pragma: py-not-win32
	self.is_restarting = True
	assert self.process.pid is not None
	os.kill(self.process.pid, signal.CTRL_C_EVENT)
	else: # pragma: py-win32
	self.process.terminate()
	self.process.join()
	self.process = get_subprocess(
	config=self.config, target=self.target, sockets=self.sockets
	)
	self.process.start()

With the changes introduced in #1584, it will hang for multiple minutes on the process.join() call. If I remove the changes, so the function looks like:

    def restart(self) -> None:
        self.process.terminate()
        self.process.join()
        self.process = get_subprocess(
            config=self.config, target=self.target, sockets=self.sockets
        )
        self.process.start()

The reload is pretty much instant, like it was on earlier versions.

[3to1null]

I can only reproduce this issue when the program is run using Pycharm. If I run it directly (either via uvicorn.run("app:app", reload=True) in Python, or with the uvicorn app:app --reload from the terminal), this issue is not present.

While it would be very nice to have this working again, I am not sure if this is something that should be fixed in Uvicorn (if this is even possible).

Edit: By enabling 'emulate terminal in output console' in Pycharm's edit run configuration dialog, the reload works as expected. However, this also seems to disable ANSI escape sequences, so the output logs look quite bad.

[Kludex]

Got it.

Please open an issue on PyCharm's issue tracker. If they tell me it's a Uvicorn bug, and explain why, we can think about the next step. 👍

[3to1null]

Done: https://youtrack.jetbrains.com/issue/PY-60962/os.killpid-signal.CRTLCEVENT-ignored-when-running-python-program-from-Pycharm.

I've added a very small program that has the same issue and does not use Uvicorn. I do not think this is a Uvicorn bug, however if Jetbrains does not want to fix this, in my opinion it might still be worth it to investigate if we can support this in Uvicorn by not using os.kill(self.process.pid, signal.CTRL_C_EVENT). Having a working reloader and being able to use Pycharm is probably the expected behaviour for a lot of developers.

btw, thank you for the quick responses :)

[rcoor]

Hello, I am getting a similar error on 0.22.0 but it happens both when I run with uvicorn.run or in the terminal, with --reload.

[altq33]

The same problem right now on FastAPI and default pycharm run settings with --reload

[Kludex]

Is there someone having this issue without pycharm?

[altq33]

Is there someone having this issue without pycharm?

No, this problem occurs when starting the server through pycharm tools, if you run the server with the same command through the terminal, --reload works instantly

[Kludex]

Thanks @altq33 :)

I'm locking this issue since people keep spamming here.

This is a pycharm issue: youtrack.jetbrains.com/issue/PY-60962/os.killpid-signal.CRTLCEVENT-ignored-when-running-python-program-from-Pycharm.

If you have an issue with Windows (not using Pycharm), please create a new issue.

(I'll not close this issue so people can be aware)