How to pause and resume a thread using the threading module?

I did some speed tests as well, the time to set the flag and for action to be taken is pleasantly fast 0.00002 secs on a slow 2 processor Linux box.

Example of thread pause test using set() and clear() events:

import threading
import time

# This function gets called by our thread.. so it basically becomes the thread init...                
def wait_for_event(e):
    while True:
        print('\tTHREAD: This is the thread speaking, we are Waiting for event to start..')
        event_is_set = e.wait()
        print('\tTHREAD:  WHOOOOOO HOOOO WE GOT A SIGNAL  : %s' % event_is_set)
        # or for Python >= 3.6
        # print(f'\tTHREAD:  WHOOOOOO HOOOO WE GOT A SIGNAL  : {event_is_set}')
        e.clear()

# Main code
e = threading.Event()
t = threading.Thread(name='pausable_thread', 
                     target=wait_for_event,
                     args=(e,))
t.start()

while True:
    print('MAIN LOOP: still in the main loop..')
    time.sleep(4)
    print('MAIN LOOP: I just set the flag..')
    e.set()
    print('MAIN LOOP: now Im gonna do some processing')
    time.sleep(4)
    print('MAIN LOOP:  .. some more processing im doing   yeahhhh')
    time.sleep(4)
    print('MAIN LOOP: ok ready, soon we will repeat the loop..')
    time.sleep(2)

There is no method for other threads to forcibly pause a thread (any more than there is for other threads to kill that thread) -- the target thread must cooperate by occasionally checking appropriate "flags" (a threading.Condition might be appropriate for the pause/unpause case).

If you're on a unix-y platform (anything but windows, basically), you could use multiprocessing instead of threading -- that is much more powerful, and lets you send signals to the "other process"; SIGSTOP should unconditionally pause a process and SIGCONT continues it (if your process needs to do something right before it pauses, consider also the SIGTSTP signal, which the other process can catch to perform such pre-suspension duties. (There may be ways to obtain the same effect on Windows, but I'm not knowledgeable about them, if any).

You can use signals: http://docs.python.org/library/signal.html#signal.pause

To avoid using signals you could use a token passing system. If you want to pause it from the main UI thread you could probably just use a Queue.Queue object to communicate with it.

Just pop a message telling the thread the sleep for a certain amount of time onto the queue.

Alternatively you could simply continuously push tokens onto the queue from the main UI thread. The worker should just check the queue every N seconds (0.2 or something like that). When there are no tokens to dequeue the worker thread will block. When you want it to start again just start pushing tokens on to the queue from the main thread again.

How to pause and resume a thread using the threading module?

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