python -c cmd will wait all process finish

Question

Codes:

File: script.py

from multiprocessing import Process


def func():
    async_process()
    print('OK')
    return 123

def func2(args):
    # do a lot of things here
    # ...
    pass

def async_process():
    p = Process(target=func2, args=args)
    p.daemon = False 
    p.start()

When I directly call the func() in Python script, I can get the returned value immediately, this is what I expect.

But, when I call the func() in command line like this:

python -c "from script import func;func()"

The command line will finish executing until the new created process finished itself. This is not I want.

How should I change the program or how should I write the script to ensure:

1. I can call the func() in command line;

2. The command line will immediately return the value when the func() is finished, and won't wait for the new created process.

3. The new created process can keeps running.

Answer 1

That's because the child process created in async_process() is not detached from its parent, hence the parent has to wait for the child to finish before exiting. If you want to create a daemon process in the Unix meaning of the term, you'll have to use the double-fork method to detach the child from its parent and hand over control to the OS' scheduler. This looks to be a decent recipe for creating Unix daemon processes in python