CODEWITHSUNDEEP
pythonpython-2.7signals
Anil Pediredla
Anil Pediredla

Reputation: 744

How to pass signal as parameter to a method in python?

My main process spawns a new process, this new process needs to terminate if SIGTERM/SIGKILL signal is sent to it. I am new to python and I don't know how to pass this signal as argument to the function.

My code is:

import os
import random
import time
import sys
import multiprocessing as mp
import psutil
import signal

def info(title):
    print (title)
    print ('module name:', __name__)
    if hasattr(os, 'getppid'):
        print ('parent process:', os.getppid())
    print ('process id:', os.getpid())

def foo(q,num):
    info('function foo')
    if type(num) is int:
       num*=2
       q.put(num)
    elif type(num) is Signal:
        print ("Terminated")
        time.sleep(10)
        os.kill(os.getpgid(pid), num)
    else :
       sys.exit("error")

def receive_signal(signum, stack):
    print 'Received:', signum

if __name__ == '__main__':
    info ("main")
    #mp.set_default('spawn')
    number = random.randint(0,100)
    print ("Initial number: ",number)
    q = mp.Queue()
    p = mp.Process(target=foo, args=(q,number))
    p.start()
    print ("Final Number: ",(q.get()))
    foo(q,signal.signal(signal.SIGTERM,recieve_signal))
    p.join()

At this moment I am struck at signal passing to function foo(q,signal.signal(signal.SIGTERM,recieve_signal))

Any help is much appreciated

Upvotes: 0

Views: 2265

Answers (1)

plamut
plamut

Reputation: 3206

As per documentation, signal.signal(...) only registers a signal, but it doesn't return any value and None gets passed to your foo() function:

foo(q,signal.signal(signal.SIGTERM,recieve_signal))

On the other hand, the second parameter to signal.signal() is a callback that is invoked when a signal of a specific type is caught (signal.SIGTERM in your case). You have already defined such handler, it's the receive_signal() function and its first parameter is the signal number. You can pass this to your foo() function by simply calling it:

def receive_signal(signum, stack):
    print 'Received:', signum
    foo(q, signum)   # NOTE: q is a module-level variable here

Upvotes: 1

Related Questions