audio: wake up the core when audio buffer is running low

And also add a function ao_need_data(), which AO drivers can call if
their audio buffer runs low.

This change intends to make it easier for the playback thread: instead
of making the playback thread calculate a timeout at which the audio
buffer should be refilled, make the push.c audio thread wakeup the core
instead.

ao_need_data() is going to be used by ao_pulse, and we need to
workaround a stupid situation with pulseaudio causing a deadlock because
its callback still holds the internal pulseaudio lock.

For AOs that don't call ao_need_data(), the deadline is calculated by
the buffer fill status and latency, as before.

0 files changed, 0 insertions, 0 deletions