How to terminate a thread when main program ends?


If I have a thread in an infinite loop, is there a way to terminate it when the main program ends (for example, when I press Ctrl+C)?

Asked By: facha



Check this question. The correct answer has great explanation on how to terminate threads the right way:
Is there any way to kill a Thread in Python?

To make the thread stop on Keyboard Interrupt signal (ctrl+c) you can catch the exception “KeyboardInterrupt” and cleanup before exiting. Like this:

except (KeyboardInterrupt, SystemExit):

This way you can control what to do whenever the program is abruptly terminated.

You can also use the built-in signal module that lets you setup signal handlers (in your specific case the SIGINT signal):

Answered By: rogeriopvl

If you make your worker threads daemon threads, they will die when all your non-daemon threads (e.g. the main thread) have exited.

Answered By: ʇsәɹoɈ

Use the atexit module of Python’s standard library to register “termination” functions that get called (on the main thread) on any reasonably “clean” termination of the main thread, including an uncaught exception such as KeyboardInterrupt. Such termination functions may (though inevitably in the main thread!) call any stop function you require; together with the possibility of setting a thread as daemon, that gives you the tools to properly design the system functionality you need.

Answered By: Alex Martelli

If you spawn a Thread like so – myThread = Thread(target = function) – and then do myThread.start(); myThread.join(). When CTRL-C is initiated, the main thread doesn’t exit because it is waiting on that blocking myThread.join() call. To fix this, simply put in a timeout on the .join() call. The timeout can be as long as you wish. If you want it to wait indefinitely, just put in a really long timeout, like 99999. It’s also good practice to do myThread.daemon = True so all the threads exit when the main thread(non-daemon) exits.

Answered By: Milean

Try to enable the sub-thread as daemon-thread.


from threading import Thread

t = Thread(target=desired_method)
t.daemon = True  # Dies when main thread (only non-daemon thread) exits.


t = Thread(target=desired_method, daemon=True).start()

Old API:


When your main thread terminates (e.g. Ctrl+C keystrokes), other threads will also be killed by the instructions above.

Answered By: Benyamin Jafari

Daemon threads are killed ungracefully so any finalizer instructions are not executed.
A possible solution is to check is main thread is alive instead of infinite loop.

E.g. for Python 3:

while threading.main_thread().isAlive():

See Check if the Main Thread is still alive from another thread.

Answered By: umi