On Tue, 2003-01-14 at 12:23, Paul Davis wrote:
> >2) start first linked stream (thus all in paralel or serial or combination
> > sequence)
> >3) poll the last stream handle for valid position
> >
> >And you don't need your complicate function.
>
> i just can't agree with that. on return from JACK's alsa_driver_wait, the
> caller knows:
>
> * how many frames are available (rounded to whole periods)
> * what delay was encountered in waiting for the data/space
> * whether an xrun occured
> * if some other error occured
>
> your proposed snd_pcm_wait_many() doesn't do any of that.
>
> i think that josh's point was perhaps a little different than you are
> thinking. i don't think he was suggesting a version of snd_pcm_wait()
> that waited on multiple handles instead of just one. i think he was
> suggesting a function that does something that most applications need:
>
> to wait until a known-sized chunk of data/space (or multiple thereof)
> is ready on *all* handles being used. since doing this involves much
> more than just calling poll(), which is fundamentally all that
> snd_pcm_wait() does, so would the multi-handle version.
You're right, that is really what I'm looking for. Maybe I could have
avoided confusion by not comparing it with snd_pcm_wait to begin with.
More than anything else, what I want to avoid having to do is set up and
interpret the results of poll() manually. For example, I infer by
reading the JACK code that POLLERR means an xrun was detected. It would
be much easier to receive this information from an ALSA function.
So perhaps a revised function signature could be:
int snd_pcm_poll( snd_pcm_t **handles, int num_handles, int timeout )
returns:
the number of frames available on all handles, or negative if an
error occured. -EPIPE if an xrun occured, -ETIMEDOUT if not all
handles were ready before timeout.
Originally I was going to write "returns the number of frames on all
handles, rounded down to the greatest complete period," but I realized
that the period size could be different for different handles.
Josh
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