[jdk18] RFR: 8278389: SuspendibleThreadSet::_suspend_all should be volatile/atomic

[Thomas Schatzl]

Hi all,

can I have reviews for this change that makes SuspendibleThreadSet::_suspend_all volatile and all accesses to it use Atomic helpers?

I found that the only getter for that member is called SuspendibleThreadSet::should_yield(), which contradicts our naming rules; to keep the change minimal (and the naming discussion out of this PR because I do not feel that _suspend_all is particularly good) I introduced a private suspend_all() method.
I can of course add some renaming in this change (but then for jdk19+ only).

Testing: gha, local compilation

Thanks,
Thomas

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Commit messages:
 - Initial change

Changes: https://git.openjdk.java.net/jdk18/pull/10/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk18&pr=10&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8278389
  Stats: 20 lines in 2 files changed: 5 ins; 1 del; 14 mod
  Patch: https://git.openjdk.java.net/jdk18/pull/10.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk18 pull/10/head:pull/10

PR: https://git.openjdk.java.net/jdk18/pull/10