using (or not) blocking mode with OSS4

[Joerg-Cyril.Hoehle at t-systems.com]

Hi,

I've had a glance at the OSS4 mmdevapi logs attached to bug #28056.
Among others, it appears that every renderer iteration takes way too
much time.  One possible explanation is that OSS write() takes a lot
of time to return, presumably in an attempt to write more than what's
possible without blocking.

If you look at AudioRenderClient_ReleaseBuffer and oss_write_data,
you'll see that it writes as much as it has, without querying
GETOSPACE.  So it can block.

open() is called without O_NONBLOCK, so write() will block when given
too much data.

I don't know yet whether O_NONBLOCK should be used. It's not what the
OSS people recommend.  One can argue that NONBLOCK is superfluous when
write is limited via GETOSPACE.
http://manuals.opensound.com/developer/open.html
http://manuals.opensound.com/developer/audio_timing.html
http://manuals.opensound.com/developer/SNDCTL_DSP_NONBLOCK.html

What do you think about using (or not) blocking mode with OSS?

W.r.t. ALSA, I'm considering keeping non-blocking mode but switch from
a periodic timer to poll(ALSA_fd, period_timeout).  Given a lot of
data, poll would return after the timeout, but when underrun is close,
this should allow to wake up closer to when data is actually needed.

Regards,
	Jörg Höhle