terminating a function call in python after n seco

Question

my python code goes like this:

def a():
    ...  
    ...  
    subprocess.call()  
    ...  
    ...  

def b():  
    ...  
    ...  

and so on.

My task:
1) If subprocess.call() returns within 3 seconds, my execution should continue the moment subprocess.call() returns.
2) If subprocess.call() does not return within 3 seconds, the subprocess.call() should be terminated and my execution should continue after 3 seconds.
3) Until subprocess.call() returns or 3 seconds finishes, the further execution should not take place.

This can be done with threads but how?

Relevant part of the real code goes like this:

...  
cmd = ["gcc", "-O2", srcname, "-o", execname];    
p = subprocess.Popen(cmd,stderr=errfile)//compiling C program  
...  
...  
inputfile=open(input,'w')  
inputfile.write(scanf_elements)  
inputfile.close()  
inputfile=open(input,'r')  
tempfile=open(temp,'w')
subprocess.call(["./"+execname,str(commandline_argument)],stdin=inputfile,stdout=tempfile); //executing C program
tempfile.close()
inputfile.close()  
...  
...  

I am trying to compile and execute a C program using python. When I am executing C program using subprocess.call() and suppose if the C program contains an infinite loop, then the subprocess.call() should be terminated after 3 seconds and the program should continue. I should be able to know whether the subprocess.call() was forcefully terminated or successfully executed so that I can accordingly print the message in the following code.

The back end gcc is of linux.

Answer 1

#!/usr/bin/python

import thread
import threading
import time
import subprocess
import os 

ret=-1

def b(arg):
    global ret
    ret=subprocess.call(arg,shell=True);

thread.start_new_thread(b,("echo abcd",))
start = time.time()


while (not (ret == 0)) and ((time.time() - start)<=3):
    pass

if (not (ret == 0)) :
    print "failed"
    elapsed = (time.time() - start)
    print elapsed
    thread.exit()

elif (ret == 0):#ran before 3 sec
    print "successful"
    elapsed = (time.time() - start)
    print elapsed

I have written the above code which is working and satisfying all my contstraints. The link https://docs.python.org/2/library/thread.html says:

thread.exit() Raise the SystemExit exception. When not caught, this will cause the thread to exit silently.

So I suppose there should be no problem of orphan processes, blocked resources, etc. Please suggest.

Answer 2

Finally the below code worked:

import subprocess
import threading
import time


def process_tree_kill(process_pid):
    subprocess.call(['taskkill', '/F', '/T', '/PID', process_pid])

def main():
    cmd = ["gcc", "-O2", "a.c", "-o", "a"];  
    p = subprocess.Popen(cmd)
    p.wait()
    print "Compiled"
    start = time.time()

    process = subprocess.Popen("a",shell=True)
    print(str(process.pid))   

    # terminate process in timeout seconds
    timeout = 3 # seconds
    timer = threading.Timer(timeout, process_tree_kill,[str(process.pid)])
    timer.start()

    process.wait()
    timer.cancel()

    elapsed = (time.time() - start)
    print elapsed

if __name__=="__main__":
    main()

Answer 3

My task:
1) If subprocess.call() returns within 3 seconds, my execution should continue the moment subprocess.call() returns.
2) If subprocess.call() does not return within 3 seconds, the subprocess.call() should be terminated and my execution should continue after 3 seconds.
3) Until subprocess.call() returns or 3 seconds finishes, the further execution should not take place.

On *nix, you could use signal.alarm()-based solution:

import signal
import subprocess

class Alarm(Exception):
    pass

def alarm_handler(signum, frame):
    raise Alarm

# start process
process = subprocess.Popen(*your_subprocess_call_args)

# set signal handler
signal.signal(signal.SIGALRM, alarm_handler)
signal.alarm(3) # produce SIGALRM in 3 seconds

try:
    process.wait() # wait for the process to finish
    signal.alarm(0) # cancel alarm
except Alarm: # subprocess does not return within 3 seconds
    process.terminate() # terminate subprocess
    process.wait()

Here's a portable threading.Timer()-based solution:

import subprocess
import threading

# start process
process = subprocess.Popen(*your_subprocess_call_args)

# terminate process in 3 seconds
def terminate():
    if process.poll() is None:
        try:
            process.terminate()
        except EnvironmentError:
            pass # ignore 

timer = threading.Timer(3, terminate)
timer.start()
process.wait()
timer.cancel()

Answer 4

If you're willing to convert your call to a Popen constructor instead of call (same way you are running gcc), then one way to approach this is to wait 3 seconds, poll the subprocess, and then take action based on whether its returncode attribute is still None or not. Consider the following highly contrived example:

import sys
import time
import logging
import subprocess

logging.basicConfig(format='%(asctime)s %(levelname)s %(message)s', level=logging.INFO)

if __name__ == '__main__':
  logging.info('Main context started')
  procCmd = 'sleep %d' % int(sys.argv[1])
  proc = subprocess.Popen(procCmd.split())

  time.sleep(3)
  if proc.poll() is None:
    logging.warning('Child process has not ended yet, terminating now')
    proc.terminate()
  else:
    logging.info('Child process ended normally: return code = %s' % str(proc.returncode))

  logging.info('Main context doing other things now')
  time.sleep(5)
  logging.info('Main context ended')

And this results in different logging output depending upon whether the child process completed within 3 seconds or not:

$ python parent.py 1
2015-01-18 07:00:56,639 INFO Main context started
2015-01-18 07:00:59,645 INFO Child process ended normally: return code = 0
2015-01-18 07:00:59,645 INFO Main context doing other things now
2015-01-18 07:01:04,651 INFO Main context ended
$ python parent.py 10
2015-01-18 07:01:05,951 INFO Main context started
2015-01-18 07:01:08,957 WARNING Child process has not ended yet, terminating now
2015-01-18 07:01:08,957 INFO Main context doing other things now
2015-01-18 07:01:13,962 INFO Main context ended

Note that this approach above will always wait 3 seconds even if the subprocess completes sooner than that. You could convert the above into something like a loop that continually polls the child process if you want different behavior - you'll just need to keep track of how much time has elapsed.