RFR: 8280828: Improve invariants in NonblockingQueue::append [v2]

[Kim Barrett]

On Tue, 8 Feb 2022 13:12:40 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

>> Kim Barrett 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 branch 'master' into append-invariant
>>  - minor comment fixes
>>  - append invariant
>
> src/hotspot/share/utilities/nonblockingQueue.inline.hpp line 200:
> 
>> 198:     // cmpxchg indicates a concurrent operation updated _head first.  That
>> 199:     // could be either a push/append or a try_pop in [Clause 1b].
>> 200:     Atomic::cmpxchg(&_head, result, (T*)NULL);
> 
> These `NULL`s could be replaced by `nullptr`.

I'm planning to do that, since this code has been going through a lot of recent churn anyway.  But I didn't want to mix that cleanup with functional changes.

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

PR: https://git.openjdk.java.net/jdk/pull/7250