android_frameworks_av/media/libnbaio

libnbaio (for "Non-Blocking Audio I/O") was originally intended to

be a purely non-blocking API.  It has evolved to now include

a few blocking implementations of the interface.



Note: as used here, "short transfer count" means the return value for

read() or write() that indicates the actual number of successfully

transferred frames is less than the requested number of frames.



Pipe

----

supports 1 writer and N readers



no mutexes, so safe to use between SCHED_NORMAL and SCHED_FIFO threads



writes:

  non-blocking

  never return a short transfer count

  overwrite data if not consumed quickly enough



reads:

  non-blocking

  return a short transfer count if not enough data

  will lose data if reader doesn't keep up



MonoPipe

--------

supports 1 writer and 1 reader



no mutexes, so safe to use between SCHED_NORMAL and SCHED_FIFO threads



write are optionally blocking:

  if configured to block, then will wait until space available before returning

  if configured to not block, then will return a short transfer count

    and will never overwrite data



reads:

  non-blocking

  return a short transfer count if not enough data

  never lose data