multiprocessing.Process.terminate not working with textual-serve

[kostrykin]

I had already observed interferences between Textual and multiprocessing.Process before, those occurred when using threaded workers (see here), so maybe there is a deeper rooted issue with multiprocessing.Process in Textual?

This here is about a different issue with multiprocessing.Process. No threads are involved!

Consider the following MWE:

import contextlib
import multiprocessing
import pathlib
import time
import sys

from textual.app import App
from textual_serve.server import Server


def run_process():
    while True:
        time.sleep(1)


class ExampleApp(App):

    def on_mount(self):
        with open('log', 'w') as file:

            def log(text):
                file.write(f'{text}\n')
                file.flush()

            p = multiprocessing.Process(target = run_process)
            log('-- 1 --')
            p.start()
            log('-- 2 --')
            p.terminate()
            log('-- 3 --')
            p.join()
            log('-- 4 --')


if __name__ == "__main__":

    if '--web' in sys.argv:
        filename = pathlib.Path(__file__).stem
        server = Server(f'python -m {filename}')
        server.serve()

    else:
        app = ExampleApp()
        app.run()

Lets say the above is stored in mwe.py.

Running this without textual-serve, like python mwe.py or python -m mwe, yields the following output:

-- 1 --
-- 2 --
-- 3 --
-- 4 --

However, running the same example with textual-serve, like python test.py --web, yields a different output:

-- 1 --
-- 2 --
-- 3 --

So obviously, when running the MWE with textual-serve, the execution gets stuck on p.join(), meaning that p.terminate() didn't work properly. The obvious workaround is to add p.kill() after the p.terminate() line, however, the behavior of the code shouldn't diverge based on whether textual-serve is being used or not, right?

---

$ python --version
Python 3.11.0

$ pip list|grep -i textual
textual                0.76.0
textual-dev            1.5.1
textual-serve          1.0.3