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Re: [Denemo-devel] Denemo hangs on quit when device is in use

From: Richard Shann
Subject: Re: [Denemo-devel] Denemo hangs on quit when device is in use
Date: Fri, 18 May 2012 10:28:29 +0100

On Fri, 2012-05-18 at 02:27 +0200, Dominic Sacré wrote:
> Hi Andreas,
> On Thursday 17 May 2012 17:41:26 Andreas Schneider wrote:
> > you can hang Denemo (0.9.4rc4) the following way:
> > * start a music player which uses the playback devive (e.g. xmms)
> > * start playback in the music player
> > * start Denemo
> > * quit Denemo
> > the program hangs; console output:
> > 
> > destroying PortMidi backend
> > PortMidi found host error...
> >   Kein passendes Gerät bzw. keine passende Adresse gefunden
> > type ENTER...
> > 
> > Hitting enter does not revive the process, you have to kill it (or do
> > fg and hit Ctrl-C).
> Thanks for reporting this.
> Ugh... The "type ENTER" message comes from PortMidi, not from Denemo 
> itself. Instead of letting us handle (or ignore) the error, PortMidi waits 
> for user input, which really is a terrible thing for a library to do.

... it as if they are deliberately being obstructive - you cannot even
use atexit() to catch the error and save your score because they hang on
stdin which may not be connected to anything. For this reason I
disallowed use in Denemo of the Input->Midi action while a score is
unsaved, in case the midi keyboard is switched off and portmidi pulls
that trick. We really should put it to the developers of portmidi that
they shouldn't be doing this by default (if indeed they need to do it at


> This "feature" can be disabled when building PortMidi, but apparently 
> distributions don't do that.
> Of course, another question is why the error occurs in the first place. 
> Which MIDI input/output devices did you configure Denemo to use? Which 
> audio subsystem (ALSA, OSS, PulseAudio, ...) do your music player and 
> Denemo use?
> Dominic
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