CODEWITHSUNDEEP
pythonmultiprocessing
roye1233
roye1233

Reputation: 110

communication between two multiprocessing in real time

I have 2 processing, I need that when something happened on one process, something else will happen on the other. For example:

import multiprocessing


def function_1(num):
    while True:
        status = False
        for i in range (num):
            if i == 100:
                status = True
            i +=1


def function_2():
    while True:
        if status == True:
            print("status changed")

if __name__ == '__main__':
    num = 101
    a = multiprocessing.Process(target=function_1,args=(num,))
    b = multiprocessing.Process(target=function_2)


    a.start()
    b.start()


    a.join()
    b.join()

This code obviously does not work, how can I make it work? I don't need one process to end and then get the result, I need the process to continue after that... is there a way to do that?

thank you!

Upvotes: 2

Views: 155

Answers (2)

blhsing
blhsing

Reputation: 106445

Instead of a using a shared variable, for the purpose of making function_2 wait until function_1 reaches a certain state, you can create a multiprocessing.Queue instance to pass to both functions, and take advantage of the fact that Queue.get blocks until the queue receives something to dequeue, and make function_1 put something into the queue once it reaches the desired state:

import multiprocessing

def function_1(queue, num):
    while True:
        for i in range(num):
            print(i)
            if i == 3:
                queue.put(None)

def function_2(queue):
    queue.get()
    print('do something')

if __name__ == '__main__':
    num = 5
    queue = multiprocessing.Queue()
    a = multiprocessing.Process(target=function_1, args=(queue, num))
    b = multiprocessing.Process(target=function_2, args=(queue,))
    a.start()
    b.start()

Upvotes: 2

Abhay Salvi
Abhay Salvi

Reputation: 1099

You forgot to add .join() after the start(). Try this : 

a.start()
b.start()

a.join()
b.join()

Upvotes: 1

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