8367240: Parallel: Refactor PSScavengeCLDClosure #27165

albertnetymk · 2025-09-09T08:59:10Z

Refactor PSScavengeCLDClosure and its "enclosing" PSScavengeFromCLDClosure so that all CLD logic is encapsulated in the CLD closure, without polluting the oop closure.

Test: tier1-3

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JDK-8367240: Parallel: Refactor PSScavengeCLDClosure (Enhancement - P4)

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Stefan Karlsson (@stefank - Reviewer)

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@fandreuz (no known openjdk.org user name / role)

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bridgekeeper · 2025-09-09T09:01:13Z

👋 Welcome back ayang! 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 · 2025-09-09T09:01:23Z

@albertnetymk This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8367240: Parallel: Refactor PSScavengeCLDClosure

Reviewed-by: stefank

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At the time when this comment was updated there had been 15 new commits pushed to the master branch:

edae355: 8246325: Add DRYRUN facility to SetupExecute
33244c8: 8344030: Improved handling of TOOLCHAIN_PATH
5c9f60d: 8367259: Clean up make/scripts and bin directory
... and 12 more: https://git.openjdk.org/jdk/compare/cc6d34b2fa299a68a05e65e25c1f41dffa67c118...master

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openjdk · 2025-09-09T09:02:50Z

@albertnetymk The following label will be automatically applied to this pull request:

hotspot-gc

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

mlbridge · 2025-09-09T09:06:56Z

Webrevs

stefank · 2025-09-09T11:15:15Z

src/hotspot/share/gc/parallel/psClosure.inline.hpp

-      // if references are left in the young gen.
-      _oop_closure.set_scanned_cld(cld);
+      // Reset before iterating oops.
+      _oop_closure._has_oop_into_young_gen = false;


I wonder if this wouldn't be cleaner if you set up a new PSScavengeFromCLDClosure here instead. Then you wouldn't have to explicitly reset _has_oop_into_young_gen here.

if (cld->has_modified_oops()) { PSScavengeFromCLDClosure oop_closure(_pm); // Clean the cld since we're going to scavenge all the metadata. cld->oops_do(&oop_closure, ClassLoaderData::_claim_none, /*clear_modified_oops*/true); if (oop_closure.has_oops_into_young_gen()) { cld->record_modified_oops(); } }

Maybe you don't have to hide PSScavengeFromCLDClosure inside PSScavengeCLDClosure. I find it more distracting that what we had before. If you don't agree with that, maybe the PSScavengeCLDClosure name could be changed so that we don't repeat the PSScavenge prefix for the internal class.

I have simplified the class name and moved it inside the do_cld method.

stefank · 2025-09-09T15:11:17Z

src/hotspot/share/gc/parallel/psClosure.inline.hpp

-};
+    public:
+      // Records whether this CLD contains oops pointing into young-gen after scavenging.
+      bool _has_oop_into_young_gen;


Comment says oops but name says oop. Maybe use _has_oops_into_young_gen?

stefank · 2025-09-09T15:16:55Z

src/hotspot/share/gc/parallel/psClosure.inline.hpp

-    _scanned_cld = cld;
-  }
+    // Scavenges a single oop in a ClassLoaderData.
+    class CLDOopClosure : public OopClosure {


This makes the do_cld function much harder to read, IMHO. So, three alternatives:

Keep the class outside PSScavengeCLDClosure, just like it was before this patch.

Have the class inside PSScavengeCLDClosure, but not in a function

Have the class inside a function inside PSScavengeCLDClosure.

I prefer (1) because it allows you to look at PSScavengeCLDClosure without having to see the details about the second class. I'm OK with (2) and like that it encapsulates the other class. I don't think we should do (3) because it significantly hurts the readability of do_cld.

I have moved the oop-closure class def outside.

stefank

Thanks for fixing the style. I've added two small nits, but otherwise I've approved the PR.

stefank · 2025-09-09T15:36:59Z

src/hotspot/share/gc/parallel/psClosure.inline.hpp

@@ -77,17 +77,19 @@ class PSRootsClosure: public OopClosure {
 typedef PSRootsClosure</*promote_immediately=*/false> PSScavengeRootsClosure;
 typedef PSRootsClosure</*promote_immediately=*/true> PSPromoteRootsClosure;

+


Suggested change

stefank · 2025-09-09T15:40:07Z

src/hotspot/share/gc/parallel/psClosure.inline.hpp

 };

 // Scavenges the oop in a ClassLoaderData.
 class PSScavengeCLDClosure: public CLDClosure {
-private:
-  PSScavengeFromCLDClosure _oop_closure;
+  PSPromotionManager* _pm;


To make the two classes consistent w.r.t. newlines.

Suggested change

PSPromotionManager* _pm;

PSPromotionManager* _pm;

fandreuz · 2025-09-10T09:45:41Z

src/hotspot/share/gc/parallel/psClosure.inline.hpp

@@ -97,43 +98,33 @@ class PSScavengeFromCLDClosure: public OopClosure {
      oop new_obj = _pm->copy_to_survivor_space</*promote_immediately=*/false>(o);
      RawAccess<IS_NOT_NULL>::oop_store(p, new_obj);

-      if (PSScavenge::is_obj_in_young(new_obj)) {
-        do_cld_barrier();
+      if (PSScavenge::is_obj_in_young(new_obj) && !_has_oops_into_young_gen) {


Why do you need to check !_has_oops_into_young_gen ?

It's to avoid writing _has_oops_into_young_gen multiple times, if it's already true. (Both versions are correct though.)

Yeah, I was curious why it's needed. What's the problem with just writing true if it's already true?

There is no problem; just redundant work.

albertnetymk · 2025-09-10T12:48:37Z

Thanks for review.

/integrate

openjdk · 2025-09-10T12:49:44Z

Going to push as commit 385c132.
Since your change was applied there have been 18 commits pushed to the master branch:

46ae1ee: 8277444: Data race between JvmtiClassFileReconstituter::copy_bytecodes and class linking
703d930: 8366980: TestTransparentHugePagesHeap.java fails when run with -UseCompressedOops
4d4e51c: 8365483: Test sun/rmi/runtime/Log/6409194/NoConsoleOutput.java sometimes fails
... and 15 more: https://git.openjdk.org/jdk/compare/cc6d34b2fa299a68a05e65e25c1f41dffa67c118...master

Your commit was automatically rebased without conflicts.

openjdk · 2025-09-10T12:49:57Z

@albertnetymk Pushed as commit 385c132.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

pgc-cld

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openjdk bot changed the title ~~8367240~~ 8367240: Parallel: Refactor PSScavengeCLDClosure Sep 9, 2025

openjdk bot added hotspot-gc [email protected] rfr Pull request is ready for review labels Sep 9, 2025

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stefank suggested changes Sep 9, 2025

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albertnetymk added 2 commits September 9, 2025 17:23

Merge branch 'master' into pgc-cld

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stefank approved these changes Sep 9, 2025

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albertnetymk deleted the pgc-cld branch September 10, 2025 12:55

stefank mentioned this pull request Sep 11, 2025

8367401: Parallel: Remove unused field in PSKeepAliveClosure #27210

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3 tasks

		@@ -77,17 +77,19 @@ class PSRootsClosure: public OopClosure {
		typedef PSRootsClosure</promote_immediately=/false> PSScavengeRootsClosure;
		typedef PSRootsClosure</promote_immediately=/true> PSPromoteRootsClosure;

8367240: Parallel: Refactor PSScavengeCLDClosure #27165

8367240: Parallel: Refactor PSScavengeCLDClosure #27165

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