check_output()
with timeout is essentially:
with Popen(*popenargs, stdout=PIPE, **kwargs) as process:
try:
output, unused_err = process.communicate(inputdata, timeout=timeout)
except TimeoutExpired:
process.kill()
output, unused_err = process.communicate()
raise TimeoutExpired(process.args, timeout, output=output)
There are two issues:
- [the second]
.communicate()
may wait for descendant processes, not just for the immediate child, see Python subprocess .check_call vs
.check_output process.kill()
might not kill the whole process tree, see How to terminate a python subprocess launched with shell=True
It leads to the behaviour that you observed: the TimeoutExpired
happens in a second, the shell is killed, but check_output()
returns only in 30 seconds after the grandchild sleep
process exits.
To workaround the issues, kill the whole process tree (all subprocesses that belong to the same group):
#!/usr/bin/env python3
import os
import signal
from subprocess import Popen, PIPE, TimeoutExpired
from time import monotonic as timer
start = timer()
with Popen('sleep 30', shell=True, stdout=PIPE, preexec_fn=os.setsid) as process:
try:
output = process.communicate(timeout=1)[0]
except TimeoutExpired:
os.killpg(process.pid, signal.SIGINT) # send signal to the process group
output = process.communicate()[0]
print('Elapsed seconds: {:.2f}'.format(timer() - start))
Output
Elapsed seconds: 1.00