Demonstrate Python subprocess polling and termination

demo_subprocess.py

#!/usr/bin/env python
# demo_subprocess.py - demonstrate Python subprocess polling and termination
# Andrew Ho (andrew@zeuscat.com)

import os, time, subprocess

sleep_for     = 5    # How long in seconds should our test subprocess sleeps
timeout_after = 3    # Send SIGTERM to the subprocess after this many seconds
poll_delay    = 0.5  # Sleep this long between polling for subprocess status

# Record begin time and fork a subprocess that sleeps for sleep_for seconds
begin = time.time()
child = subprocess.Popen(["sleep", str(sleep_for)])
print "Parent pid = " + str(os.getpid())
print "Forked child pid = " + str(child.pid)

# Poll for whether the subprocess has terminated
while(child.poll()) is None:
    elapsed = time.time() - begin
    print "Elapsed time = {0:.3f}s".format(elapsed)
    if timeout_after > 0 and elapsed > timeout_after:
        print "Terminating child"
        child.terminate()
        child.wait()
        break
    time.sleep(poll_delay)

elapsed = time.time() - begin
print "Total elapsed time = {0:.3f}s".format(elapsed)
print "Return value = " + str(child.returncode)

Change timeout_after to 0 to turn off premature termination, set the sleep_for longer to inspect the process table from another terminal session.