python how to run process in detached mode

Question

here is a example:

from multiprocessing import Process
import time


def func():
    print(\'sub process is running\')
    time.sleep(5)
    print(\'sub proc         


        

Answer 1

Python will not end if there's a non-daemon process exists.

By setting, daemon attribute before start() call, you can make the process daemonic.

p = Process(target=func)
p.daemon = True  # <-----
p.start()
print('done')

NOTE: There will be no sub process finished message printed; because the main process will terminate sub-process at exit. This may not be what you want.

You should do double-fork:

import os
import time
from multiprocessing import Process


def func():
    if os.fork() != 0:  # <--
        return          # <--
    print('sub process is running')
    time.sleep(5)
    print('sub process finished')


if __name__ == '__main__':
    p = Process(target=func)
    p.start()
    p.join()
    print('done')

Answer 2

Following the excellent answer from @falsetru, I wrote out a quick generalization in the form of a decorator.

import os
from multiprocessing import Process


def detachify(func):
    """Decorate a function so that its calls are async in a detached process.

    Usage
    -----

    .. code::
            import time

            @detachify
            def f(message):
                time.sleep(5)
                print(message)

            f('Async and detached!!!')

    """
    # create a process fork and run the function
    def forkify(*args, **kwargs):
        if os.fork() != 0:
            return
        func(*args, **kwargs)

    # wrapper to run the forkified function
    def wrapper(*args, **kwargs):
        proc = Process(target=lambda: forkify(*args, **kwargs))
        proc.start()
        proc.join()
        return

    return wrapper

Usage (copied from docstring):

import time

@detachify
def f(message):
    time.sleep(5)
    print(message)

f('Async and detached!!!')

Or if you like,

def f(message):
    time.sleep(5)
    print(message)


detachify(f)('Async and detached!!!')