Python Process Exit Code
by yaobin.wen
Recently in my project I need to use Python to spawn child processes from the main process and monitor the children’s status. If a child doesn’t exit normally, the main process will start it again. With the help of Python’s multiprocessing module, the code looks like the following:
#!/usr/bin/env python
import multiprocessing as mp
import random
import time
def _child():
while True:
time.sleep(1)
random.seed(time.time())
n = random.randint(1, 50)
if n <= 10 :
print "Child returns 0"
return 0
elif n <= 20:
print "Child returns 1"
return 1
elif n <= 30:
print "Child breaks while"
break
elif n <= 40:
raise Exception("Terminated due to exception.")
def main():
try:
child = mp.Process(target=_child, name="Producer")
child.start()
while True:
if not child.is_alive():
print "child is not alive."
print "exit code: %d" % child.exitcode
break
time.sleep(1)
except KeyboardInterrupt:
# Sleep so the child process can fully exit.
time.sleep(1)
print "child.exitcode = %s" % str(child.exitcode)
if __name__ == "__main__":
main()
I summarized the results as the table below:
| Situation | Process.exitcode | Notes |
|---|---|---|
| ‘target’ returns 0 | 0 | |
| ‘target’ returns non-zero | 0 | The return code of ‘target’ doesn’t affect the process exit code. |
| ‘target’ returns nothing | 0 | Same as the above. |
| ‘target’ returns due to exception |
1 | |
| Child process is interrupted by Ctrl-C |
1 | Process.exitcode is not ‘-N’. |
| Child process is terminated by Linux ‘kill’ command |
-N | ‘N’ is the signal number |