CODEWITHSUNDEEP
pythonsubprocesspython-2.4
BenH
BenH

Reputation: 720

subprocess.poll() not working

I cannot get subprocess.poll() to work in any situation. It keeps complaining:

Traceback (most recent call last):
  File "./JobScheduler.py", line 41, in ?
    while job1.alive():
  File "./JobScheduler.py", line 26, in alive
    if self.process.poll() is None:
AttributeError: 'NoneType' object has no attribute 'poll'

Here is my code:

#!/usr/bin/python (using version 2.4)
import sys, subprocess, threading, random, time, logging

class Command(threading.Thread):
    def __init__(self, cmd):
        super(Command, self).__init__()
        self.cmd        = cmd
        self.process    = None
        self.jobid      = None
        self.returncode = None

    def run(self):
        print "%s: starting job..." % self.getName()
        self.process = subprocess.Popen(self.cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, bufsize=0, shell=True)
        out, err = self.process.communicate()
        self.returncode = self.process.returncode
        print "Process complete:"
        print "  returncode=" + str(self.returncode)
        print "  output=" + out

    def alive(self):
        if self.process.poll() is None:
            return True
        else:
            return False

    def getJobID(self):
        return self.jobid

job1 = Command(cmd)
job1.start()
job2 = Command(cmd)
job2.start()
print "MAIN: Jobs started."

while job1.alive():
    print "job still running."
    time.sleep(10)

sys.exit(0)

I've tried using poll() in every possible way and simply cannot get it to work. The point where the while() loop is executed the processes are still running.

Sample output:

# ./JobScheduler.py 
Thread-1: starting job...
Thread-2: starting job...
MAIN: Jobs started.
Traceback (most recent call last):
  File "./JobScheduler.py", line 41, in ?
    while job1.alive():
  File "./JobScheduler.py", line 26, in alive
    if self.process.poll() is None:
 AttributeError: 'NoneType' object has no attribute 'poll'

What am I doing wrong here?

Upvotes: 1

Views: 3391

Answers (1)

Greg Hewgill
Greg Hewgill

Reputation: 992707

You are calling self.process.poll() before self.process has been assigned a value. When you start the thread, it starts by calling your run() method, but your main code continues to run. You end up calling job1.alive() before job1.run() has done any useful work yet.

Upvotes: 4

Related Questions