RFR: 8360046: Scalability issue when submitting virtual threads with almost empty tasks [v5]

[Viktor Klang]

On Thu, 7 Aug 2025 14:03:40 GMT, Doug Lea <dl at openjdk.org> wrote:

>> This set of updates reduces contention-based performance loss under heavy over-subscription, while also improving perfomance more generally.
>
> Doug Lea has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Avoid underutilization on resize

src/java.base/share/classes/java/util/concurrent/ForkJoinPool.java line 2003:

> 2001:                                     continue rescan;
> 2002:                                 if (b == (b = q.base) && a[bk] == null) {
> 2003:                                     if (a[nk] == null && a[(b + 2) & m] == null) {

@DougLea Seems worth it to add a comment around why we're looking at b + 2 here.

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PR Review Comment: https://git.openjdk.org/jdk/pull/26479#discussion_r2272712916