Multithreading - Active threads & enumerate()

Python Multithread

It is not necessary to retain an explicit handle to all of the daemon threads in order to ensure they have completed before exiting the main process.

threading.enumerate() returns a list of all Thread objects currently alive. The list includes daemonic threads, dummy thread objects created by current_thread(), and the main thread. It excludes terminated threads and threads that have not yet been started.

import threading
import time
import logging
import random

logging.basicConfig(level=logging.DEBUG,
                    format='(%(threadName)-9s) %(message)s',)

def f():
    t = threading.currentThread()
    r = random.randint(1,10)
    logging.debug('sleeping %s', r)
    time.sleep(r)
    logging.debug('ending')
    return

if __name__ == '__main__':
    for i in range(3):
        t = threading.Thread(target=f)
        t.setDaemon(True)
	t.start()

    main_thread = threading.current_thread()
    for t in threading.enumerate():
	if t is main_thread:
		continue
	logging.debug('joining %s', t.getName())
	t.join()

After threading.enumerate() gathers all active threads including the calling thread (main_thread), the code calls join() methods of those threads except the main_thread.

Output:

(daemon   ) Starting
(non-daemon) Starting
(non-daemon) Exiting

Output looks like this:

(Thread-1 ) sleeping 6
(Thread-2 ) sleeping 10
(MainThread) joining Thread-1
(Thread-3 ) sleeping 5
(Thread-3 ) ending
(Thread-1 ) ending
(MainThread) joining Thread-2
(Thread-2 ) ending
(MainThread) joining Thread-3