[crac] RFR: RCU Lock - RW lock with very lightweight read- and heavyweight write-locking [v3]

[Radim Vansa]

> This implementation is suitable for uses where the write-locking happens very rarely (if at all), as in the case of CRaC checkpoint, and we don't want to slow down regular access to the protected resource.

Radim Vansa has updated the pull request incrementally with one additional commit since the last revision:

  Add Core.defaultLock()
  
  * Add RCU lock instance that's registered as JDKResource for
    synchronization around checkpoint.
  * Allow amend the list of read-critical methods.
  * Use binary search when searching the list of read-critical methods.

-------------

Changes:
  - all: https://git.openjdk.org/crac/pull/58/files
  - new: https://git.openjdk.org/crac/pull/58/files/98732ab9..6dacbc11

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=crac&pr=58&range=02
 - incr: https://webrevs.openjdk.org/?repo=crac&pr=58&range=01-02

  Stats: 191 lines in 5 files changed: 160 ins; 9 del; 22 mod
  Patch: https://git.openjdk.org/crac/pull/58.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/58/head:pull/58

PR: https://git.openjdk.org/crac/pull/58