8369611: Remove safepoint synchronization from ParallelScavengeHeap and SerialHeap

[rm-gh-8]

Backporting JDK-8369611: Remove safepoint synchronization from ParallelScavengeHeap and SerialHeap

This PR removes unnecessary conditional STS (Safepoint Thread Synchronization) code from ParallelScavengeHeap and SerialHeap. The cleanup is possible because StringDedup threads are now derived from JavaThread (changed in JDK-8369392), eliminating the need for special conditional synchronization logic that was previously required when StringDedup threads had different threading characteristics.

This backport has internal demand.

Ran related tests on linux-x64, linux-aarch64, macos-aarch64 and windows-x64:

make test TEST=test/hotspot/jtreg/vmTestbase/gc

Results attached:

windows-x64-specific-test.log
macos-aarch64-specific-test.log
linux-x64-specific-test.log
linux-aarch64-specific-test.log

---

Progress

• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• JDK-8369611 needs maintainer approval

Issue

• JDK-8369611: Remove safepoint synchronization from ParallelScavengeHeap and SerialHeap (Enhancement - P4 - Requested)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk25u-dev.git pull/136/head:pull/136
$ git checkout pull/136

Update a local copy of the PR:
$ git checkout pull/136
$ git pull https://git.openjdk.org/jdk25u-dev.git pull/136/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 136

View PR using the GUI difftool:
$ git pr show -t 136

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk25u-dev/pull/136.diff

Using Webrev

Link to Webrev Comment

[bridgekeeper]

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[openjdk]

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See the Progress checklist in the description for automated requirements.

[openjdk]

This backport pull request has now been updated with issue from the original commit.

[openjdk]

⚠️ @rm-gh-8 This change is now ready for you to apply for maintainer approval. This can be done directly in each associated issue or by using the /approval command.

[mlbridge]

Webrevs

• 00: Full (87e2f6b1)

[rm-gh-8]

/approval request for backport of JDK-8369611: Remove safepoint synchronization from ParallelScavengeHeap and SerialHeap

This PR removes unnecessary conditional STS (Safepoint Thread Synchronization) code from ParallelScavengeHeap and SerialHeap.

This backport has internal demand.

Low risk - Fix is based on previous architectural change (JDK-8369392) with known implications, though any change to safepoint synchronization could affect GC pause times or thread coordination.

[openjdk]

@rm-gh-8
8369611: The approval request has been created successfully.

[GoeLin]

Hi Roland,
you are backporting enhancements and similar. As they are in GC, very central, I would prefer that these rather go to April or July updates, so that they are tested in 26 for some time.

[rm-gh-8]

Hi Goetz,

The earliest opportunity that meets the maintainers (and product) quality gates would be preferable.

[shipilev]

This one is one the simpler side, so we can have it in April release, I think? More complicated ones can indeed go into July release.