8351374: Improve comment about queue.remove timeout in CleanerImpl.run #23952

kimbarrett · 2025-03-07T23:17:53Z

Please review this revision of a previously puzzling comment intending to
provide the rationale for a bit of non-obvious code.

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JDK-8351374: Improve comment about queue.remove timeout in CleanerImpl.run (Enhancement - P4)

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Roger Riggs (@RogerRiggs - Reviewer)
Aleksey Shipilev (@shipilev - Reviewer) Review applies to 68c2579c

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bridgekeeper · 2025-03-07T23:18:45Z

👋 Welcome back kbarrett! 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 · 2025-03-07T23:19:34Z

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

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8351374: Improve comment about queue.remove timeout in CleanerImpl.run

Reviewed-by: rriggs, shade

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At the time when this comment was updated there had been 122 new commits pushed to the master branch:

3239919: 8350835: C2 SuperWord: assert/wrong result when using Float.float16ToFloat with byte instead of short input
47c1960: 8351689: -Xshare:dump with default classlist fails on static JDK
6b82b42: 8348598: Update Libpng to 1.6.47
2674a31: 8351891: Disable TestBreakSignalThreadDump.java#with_jsig and XCheckJSig.java on static JDK
4c6a523: 8352096: Test jdk/jfr/event/profiling/TestFullStackTrace.java shouldn't be executed with -XX:+DeoptimizeALot
d68775d: 8351995: JFR: Leftovers from removal of Security Manager
e62becc: 8350964: Add an ArtifactResolver.fetch(clazz) method
dbf47d6: 8351876: RISC-V: enable and fix some float round tests
d207ed3: 8352066: JVM.commit() and JVM.flush() exhibit race conditions against JFR epochs
0450ba9: 8351999: JFR: Incorrect scaling of throttled values
... and 112 more: https://git.openjdk.org/jdk/compare/7c9a7840ea75a9a7df3f240d063e9833f535e6ec...master

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openjdk · 2025-03-07T23:20:00Z

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

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mlbridge · 2025-03-07T23:23:24Z

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01: Full - Incremental (1c15bce8)
00: Full (68c2579c)

RogerRiggs

Nice clear description. Thanks

bchristi-git · 2025-03-10T23:14:23Z

src/java.base/share/classes/jdk/internal/ref/CleanerImpl.java

+                // If the application cleans all remaining cleanables, there
+                // won't be any references enqueued to unblock this.  Using a


I agree that calling queue.remove() with a timeout is the right approach.
But I have a question:
In the case where the Cleaner's CleanerCleanable has already run, and we get to processing the last registered cleanable on activeList:
When we do the ref.clean(), the activeList becomes empty, and we'll drop out of the while() loop. So I'm not seeing how we would attempt another queue.remove() in this case.
What am I missing?

You are missing that this loop is not the only place that potentially removes
references from activeList. The application may also do so, when directly
cleaning (as part of a close() operation or the like). So the cleaner's
cleanable may be dropped, removed, and cleaned but with live entries still in
activeList, and this loop ends up blocked in remove because there's
nothing for it to do. The application later closes all of the remaining
entries in the activeList, which doesn't cause anything to be enqueued on
the cleaner's queue, so the cleaner thread remains blocked in remove. But
now activeList is empty and will never be added to, and the queue is also
empty, and the thread is blocked in remove with nothing (other than the
timeout) to break it out.

Got it, thanks.

I'd like to suggest a small update:
If the application explicitly calls clean() on all remaining Cleanables, there...

bchristi-git · 2025-03-13T19:54:34Z

src/java.base/share/classes/jdk/internal/ref/CleanerImpl.java

+                // If the application cleans all remaining cleanables, there
+                // won't be any references enqueued to unblock this.  Using a


Got it, thanks.

I'd like to suggest a small update:
If the application explicitly calls clean() on all remaining Cleanables, there...

kimbarrett · 2025-03-18T18:59:09Z

Thanks for reviews.

kimbarrett · 2025-03-18T18:59:15Z

/integrate

openjdk · 2025-03-18T18:59:43Z

Going to push as commit 355b2f3.
Since your change was applied there have been 136 commits pushed to the master branch:

a3540be: 8352163: [AIX] SIGILL in AttachOperation::ReplyWriter::write_fully after 8319055
53c5b93: 8352180: AttachListenerThread causes many tests to timeout on Windows
b025d8c: 8350663: AArch64: Enable UseSignumIntrinsic by default
a37d843: 8352015: LIBVERIFY_OPTIMIZATION remove special optimization settings
b891bfa: 8352022: RISC-V: Support Zfa fminm_h/fmaxm_h for float16
20f1bca: 8351187: Add JFR monitor notification event
46b3d1d: 8351382: New test containers/docker/TestMemoryWithSubgroups.java is failing
558c015: 8351921: G1: Pinned regions with pinned objects only reachable by native code crash VM
f8c2122: 8352138: G1: Remove G1AddMetaspaceDependency.java test
e1bcff3: 8345687: Improve the implementation of SegmentFactories::allocateSegment
... and 126 more: https://git.openjdk.org/jdk/compare/7c9a7840ea75a9a7df3f240d063e9833f535e6ec...master

Your commit was automatically rebased without conflicts.

openjdk · 2025-03-18T18:59:51Z

@kimbarrett Pushed as commit 355b2f3.

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

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kimbarrett deleted the improve-cleanableimpl-comment branch November 24, 2025 07:08

		// If the application cleans all remaining cleanables, there
		// won't be any references enqueued to unblock this. Using a

8351374: Improve comment about queue.remove timeout in CleanerImpl.run #23952

8351374: Improve comment about queue.remove timeout in CleanerImpl.run #23952

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