how to stop one process from another in Python

Question

On a Raspberry Pi I'm running two processes which loop constantly until an input is triggered which stops one of the processes but how do I stop both processes? The only thing that works is pressing control+c in the console I can't get it to stop with code at this moment.

def stopButton():
while 1:
    wiringpi2.pinMode(52,0) 
    stopBut = wiringpi2.digitalRead(52)
    print (stopBut)
    wiringpi2.delay(500)
    if (stopBut == 0):
        stopBlink()

def stopBlink():
    redBlink = int(0)
    while (redBlink < int(20)):
        wiringpi2.digitalWrite(pin2,HIGH) 
        wiringpi2.delay(50)
        wiringpi2.digitalWrite(pin2,LOW)  
        wiringpi2.delay(50)
        redBlink += int(1)

The above code simply looks for a button press, once the button is pressed it triggers to stopBlink function which flashes a red LED 20times.

def testRunning():
while 1:
    wiringpi2.digitalWrite(pin3,HIGH) # Write HIGH to pin 2(U14 pin 2)
    wiringpi2.delay(1000)
    wiringpi2.digitalWrite(pin3,LOW)  # Write LOW to pin
    wiringpi2.delay(1000)

The above code simply flashes a blue LED on and off in a loop.

if __name__ == '__main__':
try:
    P1 = Process(target = stopButton)
    P2 = Process(target = testRunning)
    P1.start()
    P2.start()
    P1.join()
    P2.join()

Now when I hit the stopBlink function I want it to stop all other running processes but I just can't seem to get it to stop the testRunning function. I've tried adding

sys.exit(1)

To the stopBlink function but it has no affect on the other functions running.

Vincent · Accepted Answer · 2014-11-28 09:37:13Z

3

You could use multiprocessing.Event for interprocess synchronization.

Here is a similar example:

from multiprocessing import Process, Event, Lock
from time import sleep

def wait(stop_event, lock):
    with lock:
        print "Waiting 2 s..."
    sleep(2)
    with lock:
        print "Stopping processes..."
    stop_event.set()

def loop(stop_event, lock):
    while not stop_event.is_set():
        with lock:
            print "Looping every 0.5 s..."
        sleep(0.5)

if __name__ == '__main__':
    stop_event, lock = Event(), Lock()
    wait_process = Process(target=wait, args=(stop_event, lock))
    loop_process = Process(target=loop, args=(stop_event, lock))
    wait_process.start(), loop_process.start()
    wait_process.join(), loop_process.join()

I don't know if the Raspberry Pi has special requirements, but this is how you deal with python threads and processes in a more generic way.

edited Nov 28, 2014 at 9:37

answered Nov 28, 2014 at 9:25

Vincent

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