Multithreading - Timer Object

Python Multithread

The Timer is a subclass of Thread. Timer class represents an action that should be run only after a certain amount of time has passed. A Timer starts its work after a delay, and can be canceled at any point within that delay time period.

Timers are started, as with threads, by calling their start() method. The timer can be stopped (before its action has begun) by calling the cancel() method. The interval the timer will wait before executing its action may not be exactly the same as the interval specified by the user.

import threading
import time

def hello():
    print("hello, Timer")

if __name__ == '__main__':
    t = threading.Timer(3.0, hello)
    t.start()

After 3 seconds, "hello, Timer" will be printed.

The definition for the Timer looks like this:

class threading.Timer(interval, function, args=None, kwargs=None)

import threading
import time
import logging

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

def f():
    logging.debug('thread function running')
    return

if __name__ == '__main__':
    t1 = threading.Timer(5, f)
    t1.setName('t1')
    t2 = threading.Timer(5, f)
    t2.setName('t2')

    logging.debug('starting timers...')
    t1.start()
    t2.start()

    logging.debug('waiting before canceling %s', t2.getName())
    time.sleep(2)
    logging.debug('canceling %s', t2.getName())
    print 'before cancel t2.is_alive() = ', t2.is_alive()
    t2.cancel()
    time.sleep(2)
    print 'after cancel t2.is_alive() = ', t2.is_alive()

    t1.join()
    t2.join()

    logging.debug('done')

Output:

(MainThread) starting timers...
(MainThread) waiting before canceling t2
(MainThread) canceling t2
before cancel t2.is_alive() =  True
after cancel t2.is_alive() =  False
(t1       ) thread function running
(MainThread) done

Notice that the second timer(t2) is never run because it is canceled before its wake-up.

Python Multithread