Frequently I need to launch sub processes from Python. Sometimes these processes don’t work as expected, and end up blocking the program. If you want to launch a command from python, and cut it off after a certain amount of time, I recommend the threading module.

Here is how to limit the command to running for roughly 5 seconds:

#!/usr/bin/env python
import commands
import datetime
import time
import threading

class runCommand(threading.Thread):
    def run(self):
        status, output = commands.getstatusoutput('sleep 8')

if __name__ == "__main__":
    startTime = datetime.datetime.now()
    maximumRunTime = datetime.timedelta(seconds = 5)
    mythread = runCommand()
    mythread.start()

    while 1:
        if mythread.isAlive():
            print "Thread has not returned yet..."
        else:
            print "Thread is all done."
            break

        if (datetime.datetime.now() - startTime) > maximumRunTime:
            print "Thread has ran too long, giving up."
            break

        time.sleep(1)

    print "Program done"

So when we enter main, I assign the current time to startTime. Then I define maximumRunTime as a difference of 5 seconds. The thread is started, and every second we check to see if it is still running. If it is, we go ahead and check how much real time has elapsed.

Tags: Linux, programming, python