[crac] RFR: RCU Lock - RW lock with very lightweight read- and heavyweight write-locking [v7]

[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:

  Don't use SwitchPoints

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Changes:
  - all: https://git.openjdk.org/crac/pull/58/files
  - new: https://git.openjdk.org/crac/pull/58/files/984cb5d3..22e75f7c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=crac&pr=58&range=06
 - incr: https://webrevs.openjdk.org/?repo=crac&pr=58&range=05-06

  Stats: 88 lines in 1 file changed: 26 ins; 58 del; 4 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