tkinter redraw rates

fronagzen at fronagzen at
Thu Jul 18 11:10:38 CEST 2013

On Thursday, July 18, 2013 3:20:28 PM UTC+8, Christian Gollwitzer wrote:
> Am 18.07.13 06:38, schrieb fronagzen at
> > On Thursday, July 18, 2013 9:07:24 AM UTC+8, Dave Angel wrote:
> >> Nope - don't use that.  Instead, post an event on the queue, and return
> >> to the mainloop() from whence we came.
> >>           def test_thread(self):
> >>              if self.loader_thread.isAlive():
> >>                  self.root_window.after(100, self.test_thread)
> >>                  return
> > I see, though it should be noted that your method doesn't actually
> > block the rest of the even handler code from running, had to fiddle
> > with it a bit to get that to work. May I ask what exactly is the
> > rationale behind implementing it like this, though?
> Exactly this is the goal of it. Event handlers are supposed to run in as 
> short time as possible, and should never block. The reason is that you 
> want the events to be processed in the order they come in, such that he 
> user can still move the window, resize it, iconify/maximize etc.
> That said, the code still looks odd to me. I have used the Tk with 
> multithreading in the past, but directly from Tcl, and not from Python.
> The basic idea is to have the background thread (which does the work) 
> signal the main thread about its status, i.e. in the worker thread:
> for i in range(50):
>    some_odd_computation()
>    signal('progress', i)
> signal('finished')
> and in the main thread you bind() to the events fired from the worker 
> thread. That way you don't run any periodic polling.
> I fear that Tkinter has a shortcoming which does not allow this pattern 
> to be implemented. The tricky thing is to implement this signal() 
> function, which must post an event to another thread. From the C level, 
> there is Tcl_ThreadQueueEvent() which does this. It arranges for a C 
> function to be run from the event loop of another thread. From Tcl, 
> thread::send does this. To use it from Tkinter, it would be necessary to 
> create a Tcl interpreter in the worker thread *without* loading Tk.
> Some day I should dive into the innards of Tkinter to see if this is 
> possible. Then you could implement signal() simply by
> def signal(sig, data=''):
> 	tclinterp.eval('thread::send -async $mainthread {event generate . 
> <<%s>> -data {%s}'%sig%data)
> and in the main thread bind() to the virtual events.
> 	Christian
Ah, I see. Thank you for your help!

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