threads and Tkinter

[Petr Klyushkin]

Hello, Alex!

>>>>> "Alex" == Alex Martelli writes:

 Alex> Petr Klyushkin wrote:
 >> Hello again!
 >> 
 >> I have one more question about Tkinter. This time it is related
 >> with threads.  I have a program which uses Tkinter as its GUI
 >> toolkit.  It runs a separate "worker" thread for doing some
 >> time-consuming operation.  Sometimes worker thread has to update
 >> GUI.

 Alex> http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/82965

 Alex> It's also in the printed Cookbook, with some minor
 Alex> enhancements, but you can get the gist from the online-posted
 Alex> version at this URL.

Hmm, two persons already answered on this post here and it seems that
none of them even looked below the first paragraph of it because it
sounds like a FAQ.  I already know about 'periodical queue check'
solution.  I just want to know whether Tkinter is thread-safe. It
seemed to me that it is because of Tcl lock in _tkinter.c

I have received an advise by e-mail to unite thread messages and Tk
messages handling in one function by overriding mainloop() method in
Tkinter.Tk derived class.  Here is a code snippet (i've tested it and
it works nice for now on Windows and Linux):

    def mainloop(self, *args):
        """similar to mainloop, but also checks our Queue"""
        while not self.__quitMainLoop:
            while not self.thr_msg_queue.empty():
                # process message from thread
                dispatch = self.thr_msg_queue.get()
                apply(dispatch[0], dispatch[1:])
            # Do one event.  Don't block if no events available.
            # '2' means TCL_DONT_BLOCK:
            # tcl.h: #define TCL_DONT_WAIT (1<<1)
            result = self.tk.dooneevent(2)
            if result == 0:
                time.sleep(0.020)  #sleep for 20ms to allow other threads run
            if result < 0:
                break

self.thr_msg_queue is Queue.Queue instance used by worker threads to
communicate with GUI thread.  Messages are really ready-to-use
arguments for apply() function: function object and arguments.

Are there any caveats and disadvantages in this code comparing to
usual 'polling' solution?

 Alex> Alex


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