Re: avoiding VM page swaps for big sample buffers
Re: avoiding VM page swaps for big sample buffers
- Subject: Re: avoiding VM page swaps for big sample buffers
- From: David Duncan <email@hidden>
- Date: Sat, 25 Sep 2004 11:53:17 -0400
On Sep 25, 2004, at 11:34 AM, Frank (Steim) wrote:
In pre OSX systems if the user needed a big buffer he/she just
assigned as much fysical memory as available and that was it. Now of
course this is no longer possible with the result that if I load a
sample of more than an hour long (16bits stereo, 44.1 kHz) into my
buffer that is set to be 4000 seconds long (using a machine with 1Gb
of RAM), and just wanting to play from the buffer I get a
kAudioDeviceProcessorOverload notifiaction very often, resulting in
interrupted audio playback.
Is there any way my app can claim a certain amount of RAM AND to avoid
this to be swapped by the VM Manager? I tried the HoldMemory call but
to no effect.
I would say that you are using a buffer that is WAY too large. It is
possible to hold a certain amount of RAM (see man mlock) but this is
VERY rude for large amounts of memory (like a sample buffer). You would
do far better if you streamed in the data from disk during your
playback from a secondary thread and then played back from a much
smaller (say 30 sec max) buffer. There is some example code for a
lock-less ring buffer in the ComplexPlayThru example (link below). This
will let you read from your CA callback without blocking.
Complex Play Thru:
<http://developer.apple.com/samplecode/ComplexPlayThru/
ComplexPlayThru.html>
--
Reality is what, when you stop believing in it, doesn't go away.
Failure is not an option. It is a privilege reserved for those who try.
David Duncan
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