tree 88ab3ab12a8ca1f539cabed92f067cec5d00f8ea
parent 1973687350e8431d316655c00fc0701c0e1c4597
author Hans Boehm <hboehm@google.com> 1555974953 -0700
committer Hans Boehm <hboehm@google.com> 1556125484 +0000

Use single contention counter for rw mutexes

This halves the number of sequentially consistent contention counter
loads when we release a mutex.

This is more expensive than keeping the contention counter as part
of the state word. But schemes to do that either risk overflow, or
seem more subtle than we we would like at this stage. This gets us
half-way to where we would like to be. And, since we were previously
always looking at both counters anyway, it seems like low risk
change.

Bug: 111835365
Test: Build and boot AOSP, TreeHugger
Change-Id: I752859f6c51283de3ba5078233d2873a733ad4a1