In python, how can I check if a child process exited cleanly or with an error?

Question

I have some code like this

import multiprocessing as mp

processes = []
for i in range(10):
  p = mp.Process(target=my_func, args=args)
  processes.append(p)
  p.start()

for p in processes:
  p.join()

If there is a bug in my_func that causes all the threads to crash, then I want my parent process to detect that and also throw an exception. How can I detect if the process exited cleanly when I join the processes?

Answer 1

read the value of the process' exitcode :

• None if the process has not finished yet.
• 0 if the process ended successfully.
• N if the process had an error, and exited with code N.
• -N if the process was killed with the signal N . (eg. -15 if killed by SIGTERM )

For example, in your main process:

for p in processes:
    p.join()
    if p.exitcode > 0:
        raise ValueError(f'a process exited with code {p.exitcode}')

And in your runnable:

try:
    do_something()
except KnownError as _:
    exit(my_known_error_code)

Answer 2

You can check exit code after calling join() .

For example:

for p in processes:
  p.join()
  if p.exitcode is not 0:
    exit(1)

---

Reference:

• multiprocessing.Process.exitcode