RFR: 8274987 G1: reuse the newly allocated G1SegmentedArrayBuffer even if current thread failed the race [v3]

[Hamlin Li]

> This is a follow-up of JDK-8273626.
> 
> Current (original) implementation just drops the newly allocated G1SegmentedArrayBuffer if current thread fails race, but seems reuse (e.g adding to freelist) will bring some benefit.

Hamlin Li has updated the pull request incrementally with one additional commit since the last revision:

  Fix cransh on Mac; remove unnecessary code

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6034/files
  - new: https://git.openjdk.java.net/jdk/pull/6034/files/0f719443..39d20268

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6034&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6034&range=01-02

  Stats: 13 lines in 1 file changed: 1 ins; 4 del; 8 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6034.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6034/head:pull/6034

PR: https://git.openjdk.java.net/jdk/pull/6034