[all-commits] [llvm/llvm-project] 3f981f: sanitizer_common: add new mutex

[Dmitry Vyukov via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 3f981fc1861a0683eb00b442d4cad7410d4a8e59
      https://github.com/llvm/llvm-project/commit/3f981fc1861a0683eb00b442d4cad7410d4a8e59
  Author: Dmitry Vyukov <dvyukov at google.com>
  Date:   2021-07-20 (Tue, 20 Jul 2021)

  Changed paths:
    M compiler-rt/lib/sanitizer_common/sanitizer_mutex.h
    M compiler-rt/lib/sanitizer_common/tests/sanitizer_mutex_test.cpp

  Log Message:
  -----------
  sanitizer_common: add new mutex

We currently have 3 different mutexes:
 - RWMutex
 - BlockingMutex
 - __tsan::Mutex

RWMutex and __tsan::Mutex are roughly the same,
except that tsan version supports deadlock detection.
BlockingMutex degrades better under heavy contention
from lots of threads (blocks in OS), but much slower
for light contention and has non-portable performance
and has larger static size and is not reader-writer.

Add a new mutex that combines all advantages of these
mutexes: it's reader-writer, has fast non-contended path,
supports blocking to gracefully degrade under higher contention,
has portable size/performance.

For now it's named Mutex2 for incremental submission. The plan is to:
 - land this change
 - then move deadlock detection logic from tsan
 - then rename it to Mutex and remove tsan Mutex
 - then typedef RWMutex/BlockingMutex to this mutex

SpinMutex stays as separate type because it has faster fast path:
1 atomic RMW per lock/unlock as compared to 2 for this mutex.

Reviewed By: vitalybuka, melver

Differential Revision: https://reviews.llvm.org/D106231