Re: [Denemo-devel] midi input weirdness

[Richard Shann]

Ha!
I was just entering a sonata by Cannabich and it got to an A# which it
sounded on the organ, and found that indeed it had entered B-flat.
So then I remembered that I had just been writing of the dangers of
using the Modulation Wheel to change the set of sharps and flats (the
"enharmonic set").
So I saved the score and upped the modulation wheel and bingo! it
segfaulted

Program received signal SIGSEGV, Segmentation fault.
0x00000000004cac8b in scheme_output_midi_bytes (input=0x44af220)
    at ../../denemo/src/scheme-callbacks.c:4316
4316      for (i = 0, next = bytes; *next; next++)
(gdb) call gtk_main()

the call to gtk_main() brought the program back to life.

So, it seems this may be a fairly reliable way of triggering the bug.
Not one that could be automated however.
For now, stick to the buttons in the MIDI-in control panel or the
Input->MIDI menu for changing the enharmonic set.

Any threading experts who can give advice on how to debug this - please
do!

Richard

On Sun, 2014-03-23 at 15:11 +0000, Richard Shann wrote:
> On Sun, 2014-03-23 at 09:41 -0500, Jeremiah Benham wrote:
> > I may be a bit confused. I thought this was all dependant upon how the
> > modwheel is set on the midi controller.
> 
> Well, it doesn't matter how you last left the mod wheel - only changes
> to the mod wheel that you make after starting Denemo are registered.
> 
> >  When I do midi input I put the modwheel half way if I was in the key
> > of c and then move it up if I start to see flats when sharps are
> > expected and visa versa. I was not sure if that is how it is supposed
> > to work but I think I remember Richard talking about this once so I
> > tried it and it worked.
> 
> yes, the default callback for the mod wheel does exactly that. I didn't
> mention it because there is a threading bug with audio output which
> makes it crash on occasions. (It makes notes of different pitches to let
> you know which range of sharps/flats you have set, higher ones for
> sharper ranges).
> 
>  In fact I recently had this threading bug bite me while entering
> figured bass by MIDI filter, which also uses a timer to turn off a midi
> note. I discovered something remarkable: as I was running under gdb the
> segfault from the threading bug left me at the gdb prompt. I executed
> the following:
> 
> call gtk_main()
> 
> this also returned me to the prompt (the note was still playing) but
> after a couple more invocations the program was running again and I
> could save my work. I didn't write to the list about this yet, as I
> don't want to give the impression that this is something a typical user
> is likely to encounter, but it is a serious worry. I have been over the
> threading code, as best I can and did not see where the trouble lay.
> The crash occurs in the function
> 
> scheme_output_midi_bytes()
> 
> where the data are nonsensical - it is in a timer callback to turn of a
> note that has been started earlier.
> 
> If anyone can review the code to see where the threading bug arises I
> would sleep easier at night.
> 
> Richard
> 
> 
> 
> 
> 
> _______________________________________________
> Denemo-devel mailing list
> address@hidden
> https://lists.gnu.org/mailman/listinfo/denemo-devel