CODEWITHSUNDEEP
pythonpython-multiprocessing
Ginger
Ginger

Reputation: 8630

Why doesn't the Process receive the queue event?

I am trying to send data to a multi processing Process, using a queue. For some reason, the example does not work. Do you know why?

I expect the program to print out "Received something: hello" and "Received poison pill", but it never gets there. However, it does print "running" and "listening", so I know that it definitely tries to read something from the queue.

I am using Pythong 3.4

from multiprocessing import Process
import queue
import time

class EventAggregatorProcess(Process):

    def __init__(self):
        super(EventAggregatorProcess, self).__init__()
        self.event_queue = queue.Queue()

    def run(self):
        print('running')
        is_stopped=False

        while not is_stopped:
            print('listening')
            msg = self.event_queue.get()
            if msg:
                print('Received something: %s'%msg)
            else:
                print( 'Received poison pill' )
                is_stopped=True


if __name__=='__main__':
    eap = EventAggregatorProcess()
    eap.start()
    time.sleep(1)
    eap.event_queue.put('hello')
    eap.event_queue.put(None)

Upvotes: 2

Views: 41

Answers (1)

cmd
cmd

Reputation: 5830

queue module is for multi-threaded programs. These threads would all be in a single process, meaning they also share memory. (see the See Also section at the end of the docs) Your program is multiprocessing meaning you have multiple processes. These processes do not share memory. You should use the Queue from the multiprocessing library. This version of Queue handles the extra work needed for inter process communication.

from multiprocessing import Process, Queue

Upvotes: 2

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