* Paul Davis ([EMAIL PROTECTED]) wrote:
> >Also, how should programs interpret multiple poll descriptors: if the
> >poll succeeds on some descriptors but not others, does this mean the
> >stream is only "partially" ready?
>
> yes. see the internals of JACK's jack/drivers/alsa/alsa_driver.c
Honestly, I'm afraid to look at that file too carefully since it is GPL
and PortAudio is BSD. This puts me in kind of a weird situation.
> >Also, is snd_pcm_poll_descriptors_revents() understood to return the
> >events that have triggered on just *one* poll descriptor or on *all*? In
> >other words, are you ANDing bitmasks or ORing them? Right now the
> >semantics are impossible to deduce because the function just returns the
> >revents verbatim since there is only one poll descriptor.
>
> The semantics are those of POSIX poll(2): it returns the status for
> each file descriptor. ALSA's low level and mid level drivers don't
> modify this in anyway. If there 3 fd's for playback and 2 for capture,
> then the return data would indicate status for each of the 5 fd's
> (assuming you asked for it for all 5).
The prototype for this function is:
int snd_pcm_poll_descriptors_revents ( snd_pcm_t *pcm,
struct pollfd *pfds,
unsigned int nfds,
unsigned short * revents
)
Are you saying that the revents paramter is treated as an array? I was
under the impression that it is treated as a pointer to a single short.
This code fragment from test/pcm.c seems to confirm this interpretation:
static int wait_for_poll(snd_pcm_t *handle, struct pollfd *ufds, unsigned
int count)
{
unsigned short revents;
while (1) {
poll(ufds, count, -1);
snd_pcm_poll_descriptors_revents(handle, ufds, count, &revents);
if (revents & POLLERR)
return -EIO;
if (revents & POLLOUT)
return 0;
}
}
This gives me the impression that snd_pcm_poll_descriptors_revents() is a
function that somehow "summarizes" all of the pfds into a single revents
that speaks to the status of the entire PCM handle.
Josh
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