why the queue can not works for communication in this multiprocess case

Question

The following code is about the communication between two child processes by queue. I can not figure it out that why the self.q.qsize() is zero and self.q.get() is blocked in the Function "ACT"???.... Since the counter shows the queue is full...

#!/usr/bin/env python
# -*- coding: utf-8 -*-

from multiprocessing import Process
import multiprocessing
import time
from Queue import Queue

class Test():
    def __init__(self):
        self.q = Queue(1)

    def ACT(self):
        while True:
            print "B momoent queue size: %s" %self.q.qsize()
            print self.q.get()
            time.sleep(1)

    def counter(self):
        for i in range(5,10):
            if not i == 5:
                print "Hello1"
            print self.q.full()
            self.q.join()
            print "Hello2"
            self.q.put(str(i))
            print "A moment queue size: %s" % self.q.qsize()         
if __name__ == '__main__':

    foo = Test()
    qw = Process(target=foo.counter)   
    qw.start()

    qr = Process(target=foo.ACT)
    qr.start()

    qw.join()
    print "End"

Answer 1

You need to use multiprocessing.Queue .

Queue.Queue is meant for threading use. Right now you are creating and using separate queue instances in each process - there is no logic to facilitate the inter-process communication that multiprocessing.Queue provides.

multiprocessing.Queue mirrors most of Queue.Queue methods but you will have to remove join method call and possibly qsize if on OS X.