Python spawnv() with timeout

spawnvTimeout.py

#!/usr/bin/python
"""Simple module to implement spawnv with a timeout to kill the child.
Only tested on Unix. Probably won't play well with threads or many
child processes.

You can do much more subtle things with process management, but this is
easy and useful.

By Nelson Minar <nelson@monkey.org> 2004-04-11
"""

import os, signal, time

class Timeout (Exception): pass
class Error (Exception): pass

def _alarmHandler(signum, frame):
    "Handle an alarm for timing out a child process"
    if signum == signal.SIGALRM:
        raise Timeout()
    else:
        raise Error()

def spawnvTimeout(path, args, timeout):
    """spawnv a process with a timeout (in seconds).

    If the process exits before the timeout the exit code is returned
    with the semantics of os.wait().

    If the timeout fires before the process exits, a Timeout exception
    is raised and the process is sent a SIGTERM

    For example, to launch a 'sleep 5' but time out after 2 seconds:
      spawnvTimeout('/bin/sleep', ['sleep', '5'], 2)
    """

    # Install a signal handler to implement the timeout
    oldHandler = signal.signal(signal.SIGALRM, _alarmHandler)

    try:
        # Set the timeout
        signal.alarm(timeout)
        # Start the process, wait for it to finish, then clear pid flag
        pid = os.spawnv(os.P_NOWAIT, path, args)
        exitcode = os.waitpid(pid, 0)[1]
        pid = None
        # Return the code
        return exitcode
    finally:
        # Remove our alarm and reinstall the old signal handler
        signal.alarm(0)
        signal.signal(signal.SIGALRM, oldHandler)
        # If the process is still running (pid is cleared above), kill it
        if pid:
            os.kill(pid, signal.SIGTERM)

# Just a little demo of how this works. Really should be a unit test.
if __name__ == '__main__':
    def demo(sleep, timeout):
        print "\nSleeping for %d seconds, timing out in %d" % (sleep, timeout)
        now = time.time()
        try:
            exitcode = spawnvTimeout('/bin/sleep',
                                     ['sleep', str(sleep)],
                                     timeout)
            print "Finished with exit code %d" % exitcode
        except Timeout:
            print "Timed out"
        print "Execution took %.1f seconds" % (time.time() - now)
        
    print "Running demo of spawnvTimeout()"
    demo(10, 1)
    demo(2, 3)
    demo(3, 10)
    demo(2, 1)