Python multiprocessing: Will child process hang if the parent process was killed?

Question

I need help to clarify some concepts. Right now I'm using celery(a python scheduler) to run a task. Since celery has time limit for a task(300s should be default) and my task is very likely to run longer, I decided to spawn a process inside that task to do the actual work. However, what I don't know is that if during the execution of the task, I accidentally restart/stop celery server, will the process that spawned still working? Or it will become a zombie process? Please give me some details if possible. Thanks!

Edit: One more question: when you do

p = Process(target=f, args=('test',))
p.start()

Does p become a child process for current process? Or it just create an independent process?

Answer 1

I'm afraid I can only answer your first question, not being very familiar with Celery, perhaps you can find the answer in the docs.

Your question highlights the distinction between daemon and non-daemon threads.

Daemon threads are those which will not hang up the main program. They will keep working until they finish, regardless of what the main program is doing.

Non-Daemon threads are just the opposite. They must be killed before the main program ends.

This question/answer does a good job of explaining the difference and implications.

In the scope of your question, if your processes are daemon threads, they should be fine if you restart/stop your server. However, if they aren't daemon threads, you shouldn't be able to stop the celery server (assuming my understanding of daemon threads is correct)

Hopefully this helps