This PR is for the jdk26 branch, not main line. The changes in [JDK-8360046](https://bugs.openjdk.org/browse/JDK-8360046) improve the scalability of virtual threads but introduce a subtle issue with signal filtering and a regression in some SPECjbb2015 runs. [pull/28797](https://git.openjdk.org/jdk/pull/28797) is in progress for main line to address these issues.
For the jdk26 branch, the proposal is to backout the changes to ForkJoinPool from JDK-8360046 but leave the small change to VirtualThread to submit(ForkJoinTask) consistently. As part of the change, the acquire fence change to address [JDK-8372835](https://bugs.openjdk.org/browse/JDK-8372835) are proposed to be included, to avoid bringing back an issue that was fixed by JDK-8360046. So a somewhat complicated story due to jdk26 being in RDP1. Testing: test1-5, repeat testing of java/util/concurrent and java/lang/Thread/virtual tests. ------------- Commit messages: - Backout JDK-8360046, incorporate JDK-8372835 Changes: https://git.openjdk.org/jdk/pull/29187/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29187&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8375130 Stats: 470 lines in 2 files changed: 143 ins; 143 del; 184 mod Patch: https://git.openjdk.org/jdk/pull/29187.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/29187/head:pull/29187 PR: https://git.openjdk.org/jdk/pull/29187
