cython multithread behavior

[白隽]

I encountered some problems when I use cython to wrap winfsp, and my cython code run in a thread not created in python. I found while the main thread blocking (like sleep, while True, or  WaitForSingleObject  ), then my code in cython running in winfsp thread will be blocking too. I don't know what happend. I create a small demo.

multithread.pyx

import time

import threading

def thread_run():

    while True:

        try:

            time.sleep(.5)

            print("thread run")

        except KeyboardInterrupt:

            print("key board interrupt")

def create_thread():

    th = threading.Thread(target=thread_run, daemon=True)

    th.start()

    try:

        while True:

            pass

        input("press enter to exit main thread\n")

    finally:

        print("main thread exit")

        while True:

            pass

test.py

import multithread

import threading

def create_thread():

    th = threading.Thread(target=multithread.thread_run, daemon=True)

    th.start()

    try:

        while True:

            pass

        # input("press enter to exit main thread\n")

    finally:

        print("main thread exit")

        while True:

            pass

if __name__ == "__main__":

    # create_thread()

    multithread.create_thread()

if the thread didn''t create in python,  main thread blocking will blocking the thread. The winfsp use WaitForSingleObject  to wait the thread stop, but cython code run in the thread was blocking, cause a dead lock.

[da-woods]

The issue will be the global interpreter lock.

Python allows the global interpreter lock to switch after a certain number of bytecode instructions (roughly). Cython code won't release the global interpreter lock unless you specifically tell it to (or unless a Python call triggers it)

So you'd do:

```
while True:
    with nogil:  # Note that this doesn't work well on PyPy for some reason
        pass
# or
with nogil:
    WaitForSingleObject(...)
```

I believe time.sleep should release the global interpreter lock itself though.

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[白隽]

Thank you for your reply.Today I found time.sleep can release GIL,so I rewrite FspSystemStopDispatcher, set WaitForSingleObject a short timeout and time.sleep in a loop.Now I can try to modify it to 

with nogil:
    WaitForSingleObject(...).

It runs well and elegantly.

Thank u again.

da-woods <dw-...@d-woods.co.uk>于2025年9月19日 周五01:22写道：

To view this discussion visit https://groups.google.com/d/msgid/cython-users/68773996-9876-461d-903b-de26caea7697%40d-woods.co.uk.

[白隽]

Finally,I used 

with nogil:

    FspFileSystemStopDispatcher()

That’s useful!

da-woods <dw-...@d-woods.co.uk>于2025年9月19日 周五01:22写道：

The issue will be the global interpreter lock.

To view this discussion visit https://groups.google.com/d/msgid/cython-users/68773996-9876-461d-903b-de26caea7697%40d-woods.co.uk.