Question

I have several daemon threads in my Python application. When my main function exits, these daemon threads terminate (as expected) and the program closes. But I want a way to essentially “restart” my program without exiting and starting it again. Is there a way to “force close” all of my daemon threads without calling sys.exit()?

Answer 1

Mostly depends on your needs. If you want to save same type and reload
the application automatically this is not very difficult, take the
following example:

#!/usr/bin/env python

import sys, os, time

t = int(sys.argv[1])
print 'hello, I am', t
time.sleep(t)
if t > 2:
    sys.exit()
os.execl(sys.argv[0], sys.argv[0], str(t+1))

the script restarts itself while a certain condition is satisfied, then
exists. You could restart the application based on an event or a
signal, for example after a SIGHUP.

If you need also to save the current state the things are more
complicated. You can save the state of the application in a file before
restarting it and reload the state during the startup routine or you
have to instruct the daemon threads to exit on certain condition:

import threading, signal, time

should_restart = False
cond = threading.Event()
exit = threading.Event()
threads = []

def start(num=3):
    for i in range(num):
        t = threading.Thread(target=foo, args=[cond])
        threads.append(t)
        t.daemon = True
        print 'hello, I am', t.name
        t.start()

def restart(signum, frame):
    global should_restart
    should_restart = False
    cond.set()
    for thread in threads:
        thread.join()
        print 'bye bye', thread.name
    cond.clear()
    start()

def foo(should_exit):
    while not should_exit.is_set():
        time.sleep(0.2)

signal.signal(signal.SIGHUP, restart)
signal.signal(signal.SIGINT, lambda n, f: exit.set())
start()

while not exit.is_set():
    time.sleep(0.2)

I hope these two example are useful to you to better understand your needs.