Re: interrupt handing and the GUI (bug #37672)

[Daniel J Sebald]

On 11/11/2013 01:47 AM, Daniel J Sebald wrote:
> On 11/11/2013 12:35 AM, John W. Eaton wrote:
> > On 11/10/2013 10:45 PM, Daniel J Sebald wrote:
> >
> > > The last answer at this link seems to know more than the rest of us:
> > >
> > > http://stackoverflow.com/questions/12820765/can-i-send-signals-to-different-threads
> > >
> > >
> > >
> > > Maybe there is something there.
> >
> > Yes, it mentions pthread_kill. That appears to allow us to direct a
> > signal to a particular thread.
> >
> > I'm attaching a patch that seems to at least partially work for me.
> > At least interrupts seem to work now inside sleep and long running
> > functions like "inv (large_matrix)", but now I also get random
> > segfaults when typing Ctrl-C in the command window after a few
> > interrupts have been processed (it seems random).
>
> There is a lot there. The only thing that seems somewhat suspicious from
> first glance is the fact that
>
> + interpreter_thread = pthread_self ();
> +
>
> I.e., the fact that a thread might be interrupting itself. On the other
> hand, the pthread documentation says that is fine, but more than that it
> looks like the GUI thread is actually initiating the pthread_kill()
> using the above pointer so the thread really isn't interrupting itself.
>
> I'm not sure what the problem might be for the random seg fault, and yes
> pthread_kill might not be portable.

Here's a "maybe" scenario.  This article:

http://mayaposch.wordpress.com/2011/11/01/how-to-really-truly-use-qthreads-the-full-explanation/

gives a word of caution about allocating heap objects in the constructor 
of the QObject because that memory will reside in the main thread, not 
the "worker" thread.  That isn't something you've quite done, but maybe 
close:

octave_interpreter (new octave_main_thread ())
+{
+  connect (this, SIGNAL (execute_interpreter_signal (void)),
+           octave_interpreter, SLOT (execute_interpreter (void)));
+
+  connect (this, SIGNAL (interrupt_interpreter_signal (void)),
+           octave_interpreter, SLOT (interrupt_interpreter (void)));
+
+  octave_interpreter->moveToThread (main_thread);

octave_interpreter is being passed a pointer to something created in one 
thread and is then moved to another thread.  Just a guess.

Dan