Unexpected behavior in multithreading in python

Question

I am new to python and try to understand the concept of multi threading in python. As per my knowledge in Unix multi threading programming, if the main function is terminating, the threads created by main function will also get terminated irrespective of the work they are doing in the thread ( If we are not using any pthread_join() function).

But in while going through the multithreading in python , I am not seeing this feature. My threads are still running successfully even My main thread completing its work. So I want to know ,Threads in Python and Unix behave differently... or I am missing something. Please help in in understanding this thread feature in python. Here is the code in which is am using in python.

#! /usr/bin/python
import logging
import random
import threading
import time

logging.basicConfig(level=logging.DEBUG,
                format='(%(threadName)-10s) %(message)s',
               )

class Counter(object):

def __init__(self, start=0):
    self.lock = threading.Lock()
    self.value = start

def increment(self):
    logging.debug('Waiting for lock')

    # Getting the Lock
    self.lock.acquire()
    try:
        logging.debug('Acquired lock')
        self.value = self.value + 1
    finally:
       # Releasing the Lock 
        self.lock.release()



def worker(c):
    for i in range(2):
        pause = 4 
        logging.debug('Sleeping for %0.02f', pause)
        time.sleep(pause)
        c.increment()
    logging.debug('Done')



if  __name__ == '__main__':
    counter = Counter()
    for i in range(2):
        t = threading.Thread(target=worker, args=(counter,))
        t.start()

    logging.debug('Counter: %d', counter.value)

So... what was your question? This is really vague. You have described functionality, but there is no real question here. — Gareth Latty
– Gareth Latty, Commented Jun 12, 2012 at 11:54

jd. · Accepted Answer · 2012-06-12 11:52:27Z

1

You have to make the threads daemon threads.

for i in range(2):
    t = threading.Thread(target=worker, args=(counter,))
    t.setDaemon(True)
    t.start()

answered Jun 12, 2012 at 11:52

jd.

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Pierce · Accepted Answer · 2012-06-12 11:52:52Z

1

Check what the documentation says about Thread.daemon. "The entire Python program exits when no alive non-daemon threads are left."

answered Jun 12, 2012 at 11:52

Pierce

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ddzialak · Accepted Answer · 2012-06-12 11:55:08Z

0

Unfortunately, threading in python is a bit something else then linux threading. Moreover as I know according to GIL http://wiki.python.org/moin/GlobalInterpreterLock there is only one thread running at the same time (!)

Also... when mainThread is terminated it will wait for threads to finish, unless they were created as setDaemon(True) Anyway you should stop your threads by yourself, for example by try {main thread code} finally: doSomethingToStopThreads()

answered Jun 12, 2012 at 11:55

ddzialak

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