tree e975a36b49e362bed9de64d77d109578b09aa14b
parent b49d47d0a272b9f40fc9b79973769f5ed8671b35
author Glenn Kasten <gkasten@google.com> 1475438419 -0700
committer Glenn Kasten <gkasten@google.com> 1476316336 -0700

fifo: improve blocking and hysteresis

Work-in-progress to eventually allow the application to independently
specify whether or not each index (both front and rear) is also treated
as a futex, and if so whether it is single-process or multi-process.
This involves replacing mIsPrivate by an enum for futex types.
Still to do:
 - provide an API to configure this
 - better testing

Continued work on the setHysteresis() API.
Still to do:
 - better testing and debugging, especially for the read side.
 - do the right thing based on data currently in the buffer

Added available() API to return the number of frames that could
be obtain()ed.  For reader, this is the fill level.

Miscellaneous:
 - renamed sharedRear to writerRear
 - improved Doxygen comments
 - address code review comments by explaining why some paramters are
   passed by reference and some as pointers
 - updated tests
 - fixed bug: iovec was not being clear on error
 - changed default value of throttlesWriter to true

Test: tests/fifo_*
Change-Id: I0e19052abc90453ca48a0299d2c2de62468de6cb