RE: newbie trap

[Ross Clement <rclement dmu ac uk>]

Thanks Tristian and Jan for the answers.

I'm not calling 

 while ( gtk_events_pending ())
         gtk_main_iteration ();

from event handlers, they are being called from the main thread. I have
several threads running in my program. Two are the threads created by
PortAudio which read audio data into or out of ring buffers. The output
ring buffer is only written to by the main thread, the input ring buffer
is only written to by the the PortAudio thread. Audio processing is then
done by my main thread.

My gtk event handlers typically change the values of variables. The main
thread then notices that the values have changed and performs the
necessary actions. My program is (I believe) simple enough so that this
mechanism for communicating GUI events to the main thread should be
sufficient. I hope.

Very early on I noticed that if I called gtk_main_iteration() from a
secondary thread while the main thread was running gtk_main() that gtk
complained. That's when I deleted gtk_main(), and made the secondary
thread the primary one. Everything seems to be working since then, but I
was concerned about traps for young players.

I think I have avoided problems of reentrant code. E.g. I have a
"record" button. If the button is pressed again during recording or
processing of audio, the main thread will go back and start recording
again from scratch. This seems to me, without going into great detail
about my program, a reasonable user interface. Although while writing
this paragraph I went over and fixed a tiny bug by making sure that the
text of my progress bar was reset to "recording" if this happens :-)

Cheers,

Ross-c


On Wed, 2006-04-12 at 15:01 +0100, Andersen, Jan wrote:
> Ross Clement wrote:
> > Hi. I find myself writing a program that processes the gtk gui events
> > itself. E.g. code vaguely similar to the pseudo-code:
> >
> > while( large_compute_bound_job_not_finished )
> > {
> >   process_next_block_of_data();
> >   gtk_progress_bar_set_fraction( progressBar, fraction );
> >   
> >   while ( gtk_events_pending ())
> >           gtk_main_iteration ();
> > }
> >
> > Is this something that it is frequently sensible to do, or have I fallen
> > into a big newbie trap?
> I'm not sure I understand you correctly, but one thing to think about is reentrance; are the screen update 
> functions reeantrant? I remember from my Windows days (now happily in the remote past) that anything to do 
> with the desktop was not reentrant. What that means is that you can not update the screen from anything 
> other than the main thread; I have got used to simply avoiding that, so I don't know if X can handle it.
>
> One trap Windows programmers always used to fall in was to update a progress indicator whenever a network 
> packet arrived; this went well as long as the update managed to return before the next packet arrived, but 
> it caused intermittent errors and crashes when the load got too big.
>
> /jan
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