[Python-ideas] Adding threading.RepeatTimer class

[Brian Curtin]

On Thu, Jan 27, 2011 at 12:03, Daniel da Silva <ddasilva at umd.edu> wrote:

> We have a threading.Timer class which executes after a given delay and then
> terminates. I was thinking about a pre-made class that would execute, wait
> an interval, and then repeat. It would cut down on the logic people need to
> implement themselves, and make simple scripts faster.
>
> Here are some use cases:
>
> # Send a ping message to all connected clients every 120 seconds
> from server import ping_all_clients
> pinger = threading.RepeatTimer(120, ping_all_clients)
> pinger.start()
>
> # Check for updates every 3 hours
> from mymodule import check_for_updates
> update_checker = threading.RepeatTimer(60*60*3, check_for_updates)
> update_checker.start()
>
>
> I was thinking of the class having an initializer signature as follows:
>
> class threading.RepeatTimer(interval, function, args=[], kwargs={},
> limit=None)
>      Create a timer that will run function with args and kwargs and repeat
> every interval secods. If limit is
>      an integer, limits repetitions to that many calls.
>
>      cancel()
>          Stop the repeat timer. If in the middle of a call, the call is
> allowed to finish.
>
> Daniel


I'm not sure this is a good fit in the standard library. There's too much
that the implementer might want to customize for their repeating needs. For
your pinger, what if a ping fails? Keep pinging while it fails? Timeout for
a bit and try again? Increasing timeouts? Just exit? I don't think there's a
general enough use case that a repetitive timer has in order to be included.

The following will likely do what you want.

import threading

class RepeatTimer(threading.Thread):
    def __init__(self, interval, callable, *args, **kwargs):
        threading.Thread.__init__(self)
        self.interval = interval
        self.callable = callable
        self.args = args
        self.kwargs = kwargs
        self.event = threading.Event()
        self.event.set()

    def run(self):
        while self.event.is_set():
            t = threading.Timer(self.interval, self.callable,
                                self.args, self.kwargs)
            t.start()
            t.join()

    def cancel(self):
        self.event.clear()
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