Exiting from snd_pcm_wait or snd_pcm_write.

Exiting from snd_pcm_wait or snd_pcm_write.

[James Courtier-Dutton]

Hi all,

If I have an application running 2 or more threads.
Thread 1 is currently calling snd_pcm_wait() waiting for enough 
availiable space to appear in the sound buffer.
Thread 2 wants to stop thread 1 doing that( abort the snd_pcm_wait() 
call), and then wants thread 1 to restart with new data.

Can Thread 2 just call snd_pcm_drop() while thread 1 is calling 
snd_pcm_wait() ?
What about Thread 2 calling snd_pcm_reset() while thread 1 is calling 
snd_pcm_wait()?

We basically want the user seeking through an audio stream.
So, as the user seeks across the stream, a few audio frames/clippets of 
sound are played as one goes.
So, basically, the user is continually changing the source of samples 
being sent to the audio card.
In order for this changing to happen quickly, we need the some way to 
safely abort the snd_pcm_wait() and snd_pcm_write() calls.

Can we do this?

Cheers
James




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Re: Exiting from snd_pcm_wait or snd_pcm_write.

[Takashi Iwai]

At Sun, 06 Apr 2003 21:25:06 +0100,
James Courtier-Dutton wrote:
> 
> Hi all,
> 
> If I have an application running 2 or more threads.
> Thread 1 is currently calling snd_pcm_wait() waiting for enough 
> availiable space to appear in the sound buffer.
> Thread 2 wants to stop thread 1 doing that( abort the snd_pcm_wait() 
> call), and then wants thread 1 to restart with new data.
> 
> Can Thread 2 just call snd_pcm_drop() while thread 1 is calling 
> snd_pcm_wait() ?

it should be ok.  the thread 1 will be woken up after the pcm is
stopped, but POLLOUT won't be set in this case.

> What about Thread 2 calling snd_pcm_reset() while thread 1 is calling 
> snd_pcm_wait()?

this may not work (although i'm not 100% sure).
the thread 1 might lose sync.


ciao,

Takashi


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