RFR: 8269417: Minor clarification on NonblockingQueue utility [v3]

[Man Cao]

> Hi,
> 
> Could you review this change mainly based on the comments in https://github.com/openjdk/jdk/pull/4379?
> I also added an assertion to ensure and better understand why the Atomic::store() in append() is correct.
> 
> Stress tested with fastdebug build with:
> $ make test TEST="gtest:NonblockingQueueTestBasics gtest:NonblockingQueueTest" GTEST="REPEAT=-1"

Man Cao has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Merge remote-tracking branch 'origin/master' into 8269417
 - Clarify cmpxchg only fail due to try_pop.
 - Clarify NonblockingQueue's comments and add an assertion.

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4600/files
  - new: https://git.openjdk.java.net/jdk/pull/4600/files/e7890729..32d68b7b

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4600&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4600&range=01-02

  Stats: 2543 lines in 133 files changed: 1729 ins; 433 del; 381 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4600.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4600/head:pull/4600

PR: https://git.openjdk.java.net/jdk/pull/4600