tree 40df67e22f19ed6a84c44694f7c871c1a4f6c0ff
parent c5016de66b6d778dd7c292e215aad6b5c079e92c
author Hans Boehm <hboehm@google.com> 1463015712 -0700
committer Hans Boehm <hboehm@google.com> 1463526671 -0700

Fix memory order and race bugs in Refbase.h & RefBase.cpp

Convert to use std::atomic directly.

Consistently use relaxed ordering for increments, release ordering
for decrements, and an added acquire fence when the count goes to
zero.

Fix what looks like another race in attemptIncStrong:
It seems entirely possible that the final adjustment for
INITIAL_STRONG_VALUE would see e.g. INITIAL_STRONG_VALUE + 1,
since we could be running in the middle of another initial
increment.

Attempt to somewhat document what this actually does, and
what's expected from the client. Hide the documentation in
the .cpp file for now.

Remove a confusing redundant test in decWeak. OBJECT_LIFETIME_STRONG
and OBJECT_LIFETIME_WEAK are the only options, in spite of some
of the original comments.

It's conceivable that either of these issues has resulted in
actual crashes, though I would guess the probability is small.
It's hard enough to reason about this code without the bugs.

Bug: 28705989
Change-Id: I4107a56c3fc0fdb7ee17fc8a8f0dd7fb128af9d8