CODEWITHSUNDEEP
pythonmultiprocessingpython-multiprocessing
Carlo
Carlo

Reputation: 1578

Queue or event as a switch between processes

I have a system formed by 3 processes: a main one, and 2 child processes.

The first child process is constantly checking for a condition, and once this condition is verified, something happens in the second child process. This can happen multiple times.

So I was wondering...is it possible to use a mp.Event as trigger? I'm thinking of...switching it, like a True/False bool variable, and looking for it in the second process. Something like this:

main process

import multiprocessing as mp
from multiprocessing import set_start_method, Queue, Event
from p01 import P01_Initializer
from p02 import P02_Initializer
import time
import sys

def main():
    set_start_method("spawn")
    sw_event = mp.Event()

    p01 = mp.Process(target=P01_Initializer, args=(sw_event, ))
    p01.daemon = True
    p01.start()
    p02 = mp.Process(target=P01_Initializer, args=(sw_event, ))
    p02.daemon = True
    p02.start()

    ## close everything after 15 seconds
    t_start = time.time()
    while True:
        if time.time() - t_start > 15:
            p01.terminate()
            p02.terminate()
            sys.exit(0)

if __name__ == "__main__":
    main()

first child process

import time

def P01_Initializer(sw_event):
    process_01 = P01(sw_event)
    process_01.run()

class P01():
    def __init__(self, sw_event):
        self.sw_event = sw_event

    def run(self):
        while True:
            if condition:
                self.sw_event.set() ### switching it, like a bool variable

second child process

import time

def P02_Initializer(sw_event):
    process_02 = P02(sw_event)
    process_02.run()

class P02():
    def __init__(self, sw_event):
        self.sw_event = sw_event

    def run(self):
        while True:
            if self.sw_event == False:
                do nothing
            else:
                self.sw_event.set() ### switch it back to False, waiting for next occurence
                do something

Is something like this possible, or should I just use a boolean variable and pass it between processes using a Queue?

Upvotes: 0

Views: 293

Answers (1)

Carlo
Carlo

Reputation: 1578

Ok, so basically you can set/unset (?) the event by using:

sw_event.set()
sw_event.clear()

once you do that, you can check the status of the event by:

sw_event.is_set()

Upvotes: 3

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