Python threading app not terminating

Question

I have a simple python app that will not terminate if i use queue.join(). Below is the code:

import threading
import Queue

q = Queue.Queue()

for i in range(5):
    q.put("BLAH")

def worker():
    while True:
         print q.qsize()
         a = q.get()
         print q.qsize()
         q.task_done()
         print q.qsize()


for i in range(2):
    t = threading.Thread(target=worker())
    t.daemon = True
    t.start()

q.join()

I've also created a watchdog thread that print's threading.enumerate(), then sleeps for 2 seconds. The only thread left is the MainThread, and the queue size is in fact 0. This script will never terminate. I have to ctrl + z, then kill it. What's going on?

change thread creation to t = threading.Thread(target=worker) — mtadd
– mtadd, Commented Apr 19, 2013 at 6:25

FogleBird · Accepted Answer · 2013-04-19 06:26:31Z

1

t = threading.Thread(target=worker)

You want to pass a reference to the worker function, you should not call it.

answered Apr 19, 2013 at 6:26

FogleBird

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Comments

aisbaa · Accepted Answer · 2013-04-19 07:12:57Z

0

worker function does not exit, therefore it will not join. Second you probably want to join thread not queue.

I'm not an expert in python threading, but queue is just for data passing between threads.

answered Apr 19, 2013 at 7:12

aisbaa

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1 Comment

Austin Phillips Over a year ago

Python's Queue does in fact allow the join operation, which indicates that all queued items have been popped with a corresponding call to task_done. Further, because a daemon thread is used, the main application will be allowed to exit even though the daemon thread is still running.

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