Re: ThreadSafe Note Scheduling Code (Was Re: Threading)
Re: ThreadSafe Note Scheduling Code (Was Re: Threading)
- Subject: Re: ThreadSafe Note Scheduling Code (Was Re: Threading)
- From: Philippe Wicker <email@hidden>
- Date: Fri, 8 Aug 2003 22:18:36 +0200
On Friday, August 8, 2003, at 08:52 PM, Chris Rogers wrote:
Hi Robert,
Yes, the code Bill posted is only thread-safe with two threads
involved,
a queuing thread and a rendering thread. The thread safety breaks down
if you want to support multiple threads other than the render thread.
However, I think the code covers the 90% usage case, and I think it
would be
quite considerably more expensive to expect all MusicDevice AudioUnits
to
support multiple "secondary" threads, since this would requires thread
synchronization locks which in addition to being expensive could
block the render thread which would be really bad! I think at this
point,
the host would have to provide responsibility for the thread
synchronization,
and luckily I think this would rarely be necessary.
I think the code is completely thread safe for one single queuing
thread and one rendering thread, although it's always nice to have
people look at it to verify our assumptions...
This kind of queue is still thread-safe when used in a (n producers / 1
consumer) configuration provided that a lock (a mutex) is added on the
producer side. This mutex protects against concurrent producers
accesses without any blocking side effect on the consumer side. So
provided this additional mutex, the pthread_mutex_init and
pthread_mutex_lock/unlock calls at the correct places, the same code
could be used with n midi threads and 1 render thread. At first glance,
it should be enough to enclose the code of QueueExtendedNoteOn and
QueueExtendedNoteOff with a pair of pthread_mutex_lock/unlock.
Chris Rogers
Core Audio
Apple Computer
Maybe I'm missing something - but can somebody point out where the
thread safety comes in? What about the possibility that the AU is fed
MIDI data from multiple threads for example a MIDI Clock tick from
one MIDI source and MIDI notes from another?
And I agree with Urs that this queue should be always used which is
why I suggested a queue be part of the framework rather than
something to be added by each Music AU implementor.
Thanks,
Robert.
Philippe Wicker
email@hidden
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