Question

I have simple PyGTK app. Since I have to run multiple periodic tasks to fetch some data and refresh GUI, I extended Thread like this:

class MyThread(threading.Thread):        
    def __init__(self):
        threading.Thread.__init__(self)
        self.setDaemon(True)
        self.event = threading.Event()
        self.event.set()

    def run(self):
        while self.event.is_set():
            timer = threading.Timer(60, self._run)   
            timer.start()
            timer.join()

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

    def _run(self):
        gtk.threads_enter()
        # do what need to be done, fetch data, update GUI
        gtk.threads_leave()

I start threads on app bootstrap, save them in some list and cancel them before exit. This works just perfect.

But now I want to add refresh button which will force one of the threads to run immediately and not wait period of time to be run, if not currently running.

I tried to do that by adding bool var to MyThread to indicate whether a thread is running or not (set before _run, reset on complete), and then just call MyThread._run() if not running, but that causes my app to become unresponsive and _run task to never finish execution.

I’m not sure why this happens. What is the best way to solve this problem? It would be also fine if I can make refresh running in background so it does not block GUI.

Maybe to call run and pass in number of seconds to 1 so timer can trigger it sooner?

Answer 1

Instead of using a Timer, use another Event object in combination with a timeout. You can then set that event from within your button callback. The following code illustrates this (I’ve stripped your cancelling code to keep it short):

import threading

class MyThread(threading.Thread):

    def __init__(self):
        threading.Thread.__init__(self)
        self.sleep_event = threading.Event()
        self.damon = True

    def run(self):
        while True:
            self.sleep_event.clear()
            self.sleep_event.wait(60)
            threading.Thread(target=self._run).start()

    def _run(self):
        print "run"

my_thread = MyThread()
my_thread.start()

while True:
    raw_input("Hit ENTER to force execution\n")
    my_thread.sleep_event.set()

By default “run” will be printed every 60 seconds. If you hit ENTER it will be printed immediately, and then again after 60 seconds, etc.