8367848: Parallel: Use NMethodToOopClosure during Young GC #27336

albertnetymk · 2025-09-17T09:00:22Z

Replace MarkingNMethodClosure with NMethodToOopClosure during young-gc. After that, a new local ThreadsClaimTokenScope is introduced instead of StrongRootsScope to make the thread-claim-token logic visible in the current context.

Test: tier1-3

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Issue

JDK-8367848: Parallel: Use NMethodToOopClosure during Young GC (Enhancement - P4)

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Stefan Karlsson (@stefank - Reviewer)
Thomas Schatzl (@tschatzl - Reviewer)

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bridgekeeper · 2025-09-17T09:02:04Z

👋 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 · 2025-09-17T09:02:24Z

@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:

8367848: Parallel: Use NMethodToOopClosure during Young GC

Reviewed-by: stefank, tschatzl

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At the time when this comment was updated there had been 44 new commits pushed to the master branch:

48d394a: 8356995: Provide default methods min(T, T) and max(T, T) in Comparator interface
898fcff: 8367325: [s390x] build failure due to JDK-8361376
5855fd2: 8367784: java/awt/Focus/InitialFocusTest/InitialFocusTest1.java failed with Wrong focus owner
... and 41 more: https://git.openjdk.org/jdk/compare/976207df1fcebf76a5f732b26424d6a4896b359e...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

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openjdk · 2025-09-17T09:03:24Z

@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 · 2025-09-17T09:06:59Z

Webrevs

stefank · 2025-09-17T14:41:11Z

src/hotspot/share/gc/parallel/psScavenge.cpp

+  struct ThreadsClaimTokenScope : StackObj {
+    ThreadsClaimTokenScope() {
+      Threads::change_thread_claim_token();
+    }
+    ~ThreadsClaimTokenScope() {
+      Threads::assert_all_threads_claimed();
+    }
+  };


Could this class be placed in Threads together with these functions:

static uintx thread_claim_token() static void change_thread_claim_token(); static void assert_all_threads_claimed() NOT_DEBUG_RETURN; static void possibly_parallel_oops_do(bool is_par, OopClosure* f, NMethodClosure* cf);

There's other GC code that could benefit from using this helper.

Moved to threads.hpp

stefank · 2025-09-17T15:05:16Z

src/hotspot/share/gc/parallel/psScavenge.cpp

@@ -234,7 +234,7 @@ class PSThreadRootsTaskClosure : public ThreadClosure {
 };

 class ScavengeRootsTask : public WorkerTask {
-  StrongRootsScope _strong_roots_scope; // needed for Threads::possibly_parallel_threads_do
+  Threads::ThreadsClaimTokenScope _threads_claim_token_scope; // needed for Threads::possibly_parallel_threads_do


I wonder if this class could just be named ClaimTokenScope so that we don't need to see the word Threads twice?

Threads::ThreadsClaimTokenScope

vs

Threads::ClaimTokenScope

OTOH, the function is named change_thread_claim_token. Maybe the second reviewer could weigh in on this.

ThreadsClaimTokenScope should only be used by GC code, so I can put it in GC-shared code instead of threads.

Well, Threads::change_thread_claim_token() are also only used by GC but it is still located in Threads. Another alternative could be to put ThreadsClaimTokenScope at the end of threads.hpp.

Moved to the end of threads.hpp.

stefank · 2025-09-17T15:05:27Z

src/hotspot/share/runtime/threads.hpp

+  struct ThreadsClaimTokenScope : StackObj {
+    ThreadsClaimTokenScope() {
+      Threads::change_thread_claim_token();
+    }
+    ~ThreadsClaimTokenScope() {
+      Threads::assert_all_threads_claimed();
+    }
+  };


I wonder if the implementation should be moved to the cpp file or if we consider this small enough to include here?

stefank · 2025-09-17T15:07:55Z

Adding runtime because this now also touches the Threads class.
/label add hotspot-runtime

openjdk · 2025-09-17T15:10:13Z

@stefank
The hotspot-runtime label was successfully added.

albertnetymk · 2025-09-19T07:34:53Z

Thanks for review.

/integrate

openjdk · 2025-09-19T07:37:18Z

Going to push as commit 28879d3.
Since your change was applied there have been 44 commits pushed to the master branch:

48d394a: 8356995: Provide default methods min(T, T) and max(T, T) in Comparator interface
898fcff: 8367325: [s390x] build failure due to JDK-8361376
5855fd2: 8367784: java/awt/Focus/InitialFocusTest/InitialFocusTest1.java failed with Wrong focus owner
... and 41 more: https://git.openjdk.org/jdk/compare/976207df1fcebf76a5f732b26424d6a4896b359e...master

Your commit was automatically rebased without conflicts.

openjdk · 2025-09-19T07:37:27Z

@albertnetymk Pushed as commit 28879d3.

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

pgc-nmethod

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openjdk bot changed the title ~~8367848~~ 8367848: Parallel: Use NMethodToOopClosure during Young GC Sep 17, 2025

openjdk bot added hotspot-gc [email protected] rfr Pull request is ready for review labels Sep 17, 2025

stefank reviewed Sep 17, 2025

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albertnetymk deleted the pgc-nmethod branch September 19, 2025 07:39

8367848: Parallel: Use NMethodToOopClosure during Young GC #27336

8367848: Parallel: Use NMethodToOopClosure during Young GC #27336

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