How to create a background threaded on interval function call in python?

Question

I am trying to implement a heartbeat call that works in the background. How do I create a threaded on interval call of say every 30 seconds, which calls the following function:

self.mqConn.heartbeat_tick()

Also how would I stop this thread?

Many thanks.

Answer 1

Use a thread containing a loop

from threading import Thread
import time

def background_task():
    while not background_task.cancelled:
        self.mqConn.heartbeat_tick()
        time.sleep(30)
background_task.cancelled = False

t = Thread(target=background_task)
t.start()

background_task.cancelled = True

---

Alternatively, you could subclass timer, to make cancelling easy:

from threading import Timer

class RepeatingTimer(Timer):
    def run(self):
        while not self.finished.is_set():
            self.function(*self.args, **self.kwargs)
            self.finished.wait(self.interval)


t = RepeatingTimer(30.0, self.mqConn.heartbeat_tick)
t.start() # every 30 seconds, call heartbeat_tick

# later
t.cancel() # cancels execution

Answer 2

Or you could use the Timer class in the threading module:

from threading import Timer

def hello():
    print "hello, world"

t = Timer(30.0, hello)
t.start() # after 30 seconds, "hello, world" will be printed
t.cancel() # cancels execution, this only works before the 30 seconds is elapsed

This will not start every x seconds, rather it delays the thread for execution in x seconds. But you can still put that in a loop and use t.is_alive() to see its status.

Answer 3

A quick followup to Eric's answer: you can't subclass Timer in python 2, since it's actually a light function wrapper around the true class: _Timer. If you do you'll get the issue that pops up in this post.

Using _Timer instead fixes it:

from threading import _Timer

class RepeatingTimer(_Timer):
    def run(self):
        while not self.finished.is_set():
            self.function(*self.args, **self.kwargs)
            self.finished.wait(self.interval)


t = RepeatingTimer(30.0, self.mqConn.heartbeat_tick)
t.start() # every 30 seconds, call heartbeat_tick

# later
t.cancel() # cancels execution