signal.CTRL_BREAK_EVENT is causing "the handle is invalid" and won't shutdown

[danrossi]

In a consoleless pyinstaller built application. My program won't shut down its process when using

sig = signal.CTRL_BREAK_EVENT
os.kill(os.getpid(), sig)

With an error

[WinError 6] The handle is invalid

The documentation about signal is poor and confusing. the example code is poor and doesn't reference os.kill. I am fairly certain it was working at some stage. When exiting the app calling the code above in powershell it's ok.

https://pyinstaller.org/en/v6.3.0/feature-notes.html#signal-handling-in-console-windows-applications-and-onefile-application-cleanup

Any ideas ?

[rokm]

CTRL_C_EVENT and CTRL_BREAK_EVENT are console events, and as implied by the name, require a console.

[rokm]

I think the "recommended" approach would be to look into finishing/shutting down your tasks (the app and the server), and exiting the event loop, instead of having the application try to terminate itself via signals.

[danrossi]

In my uvicorn app. I have a callback for shutdown. But I need to emit a signal to trigger that shutdown method. Then I can call loop.stop(). The shutdown task ends all active tasks. It doesn't seem to be called when using SIGINT.

app = Application(on_startup=[startup_task], on_shutdown=[shutdown_task])

async def shutdown_task():

    try:
        tasks = [t for t in asyncio.all_tasks() if t is not asyncio.current_task()]
        [task.cancel() for task in tasks]
        logger.debug("Canceling outstanding tasks")
        await asyncio.gather(*tasks)
        logger.info("shutting down")
        loop.stop()
    except asyncio.exceptions.CancelledError:
        logger.debug("Cancelled")
        pass
    pass

async def startup_task():
    logger.debug("Startup") 
    pass
    ```
    
    ```
def on_exit(self) -> None:

        if sys.platform == 'darwin':
            sig = signal.SIGKILL
        else:
            sig = signal.SIGINT
            #sig = signal.CTRL_BREAK_EVENT

        os.kill(os.getpid(), sig)

[danrossi]

I can't seem to trigger the shutdown callback to stop the loop with SIGTERM either only break calls it I think.

sig = signal.SIGTERM
            #sig = signal.CTRL_BREAK_EVENT
        os.kill(os.getpid(), sig)

[rokm]

On Windows, both SIGINT and SIGTERM result in process termination via TerminateProcess; there is no way to gracefully interrupt the process.

So if you have no option to programmatically stop your uvicorn server (which seems to be the reason for this signal-based approach), you are out of luck, since the alternative (the console control events) require a console. This has nothing to with PyInstaller, though; you would run into same issues if you ran your code in windowed/noconsole python interpreter (pythonw).

[danrossi]

I just checked the compiled app. And SIGTERM stops the process but may not be calling uvicorn's signal handler for shutting down.

[danrossi]

Im researching more. Windows is problematic. I forgot to mention its a startlette app. the on_shutdown doesn't get triggered for any of the signal methods. SIGINT and SIGTERM exits the processes but may need to create my own handler.

[rokm]

FWIW, it seems to me that uvicorn's signal handler is simply setting a uvicorn.server.Server.should_exit boolean, which then causes main loop to exit:

https://github.com/Kludex/uvicorn/blob/8ae0bcbecb0a655789abf0c2dd4200848fc68a30/uvicorn/server.py#L321
https://github.com/Kludex/uvicorn/blob/8ae0bcbecb0a655789abf0c2dd4200848fc68a30/uvicorn/server.py#L333-L338

If you have a reference to the server object (and if not, you can always store it), you can try setting this boolean in your application's on_exit() handler and try to shut down the server without having to resort to signals.