[Vm-dev] re: Mac OS Cocoa MIDI Plugin

Craig Latta craig at blackpagedigital.com
Fri May 20 11:02:24 UTC 2016

Hi Eliot--

> First, Cog on Linux in 2010 had to use the itimer heartbeat because
> pthreads only supported one priority, and so the heartbeat couldn't
> be a thread. The itimer heartbeat works by delivering signals, and
> ALSA didn't cope with interrupted system calls.  Second, the X11 GUI
> and socket i/o depend on delivering SIGIO and ALSA interfered with
> signal delivery.  When ALSA loaded it installed its own SIGIO handler
> but didn't check for any previously installed handler and so broke
> the system.
> To fix these two problems I had to maintain my own corrected version
> of the ALSA code, we were under time pressure and this was quicker
> than trying to engage the ALSA author(s) to correct the code.

     Aha, I'm curious to know if your signal fix involved a separate
host process for ALSA, and/or the SIGRTMIN signals, as mentioned in [1].
I guess I'll find out soon enough. :)

> So if ALSA is the only game in town I guess we must get the code
> fixed.  How is ALSA maintained and by whom?

     The project hosts a git repository[2]. The core team is listed at [3].

> Is the code still broken as described above?

     I suspect so; do you have a minimal regression test I can build and

> > I found an enlightening and sad summary of the Linux audio
> > processing architecture[4] which, although written in 2010, seems
> > to jibe with the current Wikipedia pages for ALSA[5],
> > PulseAudio[6], JACK[7] (another sound server), and OSS[8], and with
> > a similarly sad Linux MIDI summary[9].
> I'll try and find time to read this.  Care to summarize?

     Oh, just that there are far too many pieces, with feature sets that
overlap and build on each other in ever stranger ways over time. It's
easy to think that one piece is "standard" for a particular role, when
it actually does something very different. But at least there are
reasonable overviews now.

     For Linux Squeak MIDI, the upshot is that we want to play nicely
with ALSA, and PortMIDI is a good way to do that. More broadly, using
the PortMedia libraries/APIs would make Squeak audio and MIDI much more
pleasant on Linux, Windows, and Mac OS. Indeed, let's start by getting
your ALSA bug confirmed for 2016, then probably get your fix integrated.

     thanks again,


[1] https://tinyurl.com/z2o58km (linuxquestions.org)
[2] http://www.alsa-project.org/main/index.php/GIT_Server
[3] http://www.alsa-project.org/main/index.php/Alsa_Team

[4] http://tuxradar.com/content/how-it-works-linux-audio-explained
[5] https://en.wikipedia.org/wiki/Advanced_Linux_Sound_Architecture
[6] https://en.wikipedia.org/wiki/PulseAudio
[7] https://en.wikipedia.org/wiki/JACK_Audio_Connection_Kit
[8] https://en.wikipedia.org/wiki/Open_Sound_System
[9] http://www.tedfelix.com/linux/linux-midi.html

Craig Latta
Black Page Digital
craig at blackpagedigital.com
+31   6 2757 7177 (SMS ok)
+ 1 415  287 3547 (no SMS)

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