8325587: Shenandoah: ShenandoahLock should allow blocking in VM

[mmyxym]

Clean backport of fixing rare long hand shake while mutator threads in heavy contention on ShenandoahLock.

Additional testing:

• Linux aarch64 server fastdebug, hotspot/jtreg/tier1 with +UseShenandoahGC

---

Progress

• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• JDK-8325587 needs maintainer approval

Issue

• JDK-8325587: Shenandoah: ShenandoahLock should allow blocking in VM (Bug - P3)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk21u-dev.git pull/560/head:pull/560
$ git checkout pull/560

Update a local copy of the PR:
$ git checkout pull/560
$ git pull https://git.openjdk.org/jdk21u-dev.git pull/560/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 560

View PR using the GUI difftool:
$ git pr show -t 560

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk21u-dev/pull/560.diff

Webrev

Link to Webrev Comment

[bridgekeeper]

👋 Welcome back lmao! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

❗ This change is not yet ready to be integrated.
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]

⚠️ @mmyxym 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 (cb87b771)

[mmyxym]

/approval request Clean backport of fixing rare long hand shake while mutator threads in heavy contention on ShenandoahLock. Risk is quite low.

[openjdk]

@mmyxym
8325587: The approval request has been created successfully.

[GoeLin]

Please backport to 22 first.

[shipilev]

Too early for 21u-dev anyway; there are follow-up improvements that we want to resolve first, and then backport all of them at once, so that JDK 21 is not in some intermediate state.

[RealCLanger]

Too early for 21u-dev anyway; there are follow-up improvements that we want to resolve first, and then backport all of them at once, so that JDK 21 is not in some intermediate state.

Rampdown for 21.0.4 started. So, @shipilev, is it time now to approve this for 21.0.5 or shall we wait?

[shipilev]

Rampdown for 21.0.4 started. So, @shipilev, is it time now to approve this for 21.0.5 or shall we wait?

We are working on JDK-8331411, I would instead prefer wait for that to complete and then backport both back to back.

[RealCLanger]

Rampdown for 21.0.4 started. So, @shipilev, is it time now to approve this for 21.0.5 or shall we wait?

We are working on JDK-8331411, I would instead prefer wait for that to complete and then backport both back to back.

OK, then I'll remove the fix-request label for now. Please re-request when this is ready.