Concurrency API, ReadWriteLock
Revert "Concurrency API, ReadWriteLock"

This reverts commit 277fb6df07bdf19badbf76f5d3c091859bca70a7.
Revert "Revert "Concurrency API, ReadWriteLock""

This reverts commit 2696510b5ff4874d06d564524159ed2d587250f1.
Revert "Revert "Revert "Concurrency API, ReadWriteLock"""

This reverts commit 65a4e833c362d5fbf28a684665894975eee9f93d.