How to limit program's execution time when using subprocess?

Question

I want to use subprocess to run a program and I need to limit the execution time. For example, I want to kill it if it runs for more than 2 seconds.

For common programs, kill() works well. But if I try to run /usr/bin/time something, kill() can’t really kill the program.

My code below seems doesn’t work well. The program is still running.

import subprocess
import time

exec_proc = subprocess.Popen("/usr/bin/time -f \"%e\\n%M\" ./son > /dev/null", stdout = subprocess.PIPE, stderr = subprocess.STDOUT, shell = True)

max_time = 1
cur_time = 0.0
return_code = 0
while cur_time <= max_time:
    if exec_proc.poll() != None:
        return_code = exec_proc.poll()
        break
    time.sleep(0.1)
    cur_time += 0.1

if cur_time > max_time:
    exec_proc.kill()

Answer 1

If you're using Python 2.6 or later, you can use the multiprocessing module.

from multiprocessing import Process

def f():
    # Stuff to run your process here

p = Process(target=f)
p.start()
p.join(timeout)
if p.is_alive():
    p.terminate()

---

Actually, multiprocessing is the wrong module for this task since it is just a way to control how long a thread runs. You have no control over any children the thread may run. As singularity suggests, using signal.alarm is the normal approach.

import signal
import subprocess

def handle_alarm(signum, frame):
    # If the alarm is triggered, we're still in the exec_proc.communicate()
    # call, so use exec_proc.kill() to end the process.
    frame.f_locals['self'].kill()

max_time = ...
stdout = stderr = None
signal.signal(signal.SIGALRM, handle_alarm)
exec_proc = subprocess.Popen(['time', 'ping', '-c', '5', 'google.com'],
                             stdin=None, stdout=subprocess.PIPE,
                             stderr=subprocess.STDOUT)
signal.alarm(max_time)
try:
    (stdout, stderr) = exec_proc.communicate()
except IOError:
    # process was killed due to exceeding the alarm
finally:
    signal.alarm(0)
# do stuff with stdout/stderr if they're not None