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8275329: ZGC: vmTestbase/gc/gctests/SoftReference/soft004/soft004.java fails with assert(_phases->length() <= 1000) failed: Too many recored phases? #6358

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@pliden pliden commented Nov 11, 2021

In ZGC, the phases the "Pause Mark End" and "Concurrent Mark Continue" can be executed multiple times in the same GC cycle. This can happen for two reasons:

  1. After "Concurrent Mark Continue" has terminated, but before "Pause Mark End" has started, a SoftReference or a WeakReference is resurrected by a call to Reference.get() from a Java thread.

  2. A Java thread "hides" work from the GC worker threads doing marking, by detaching unmarked objects from the graph and push it to a thread local mark stack, that the GC needs to flush out. An example of this is when a Java thread continuously removes the first element in a single linked list that hasn't been marked yet.

The above events are typically rare, but it is possible to write a program that causes the above GC phases to be executed a large number of times. The test that failed (soft004.java) runs into case 2 above, where it has ~50,000,000 SoftReferences in the reference processing pending list (a single linked list) and continuously removes the first element until the list if empty. This causes more than 1000 "Pause Mark End" attempt to happen. For that reason, we don't want TimePartitions to assert if there are more than 1000 phases. This patch disables the assert in question if ZGC is used. An alternative would be to remove the assert completely, but @stefank preferred to just disable it for ZGC.


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  • JDK-8275329: ZGC: vmTestbase/gc/gctests/SoftReference/soft004/soft004.java fails with assert(_phases->length() <= 1000) failed: Too many recored phases?

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…a fails with assert(_phases->length() <= 1000) failed: Too many recored phases?
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@bridgekeeper bridgekeeper bot commented Nov 11, 2021

👋 Welcome back pliden! 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.

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@openjdk openjdk bot commented Nov 11, 2021

@pliden 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.

@openjdk openjdk bot added the hotspot-gc label Nov 11, 2021
@pliden pliden marked this pull request as ready for review Nov 11, 2021
@openjdk openjdk bot added the rfr label Nov 11, 2021
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@mlbridge mlbridge bot commented Nov 11, 2021

Webrevs

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@openjdk openjdk bot commented Nov 11, 2021

@pliden 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:

8275329: ZGC: vmTestbase/gc/gctests/SoftReference/soft004/soft004.java fails with assert(_phases->length() <= 1000) failed: Too many recored phases?

Reviewed-by: stefank, eosterlund

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 2 new commits pushed to the master branch:

  • 2ca4ff8: 8244202: Implementation of JEP 418: Internet-Address Resolution SPI
  • c29cab8: 8276112: Inconsistent scalar replacement debug info at safepoints

Please see this link for an up-to-date comparison between the source branch of this pull request and the master branch.
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 openjdk bot added the ready label Nov 11, 2021
fisk
fisk approved these changes Nov 11, 2021
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@pliden pliden commented Nov 12, 2021

Thanks for reviewing!

/integrate

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@openjdk openjdk bot commented Nov 12, 2021

Going to push as commit 6b833db.
Since your change was applied there have been 10 commits pushed to the master branch:

  • 1e941de: 8275197: Remove unused fields in ThaiBuddhistChronology
  • 6954b98: 8186670: Implement _onSpinWait() intrinsic for AArch64
  • 3445e50: 8276265: jcmd man page is outdated
  • 0ca0acf: 8276947: Clarify how DateTimeFormatterBuilder.appendFraction handles value ranges
  • b0d7a9d: 8276994: java/nio/channels/Channels/TransferTo.java leaves multi-GB files in /tmp
  • 8aae88b: 8276763: java/nio/channels/SocketChannel/AdaptorStreams.java fails with "SocketTimeoutException: Read timed out"
  • 6f35eed: 8079267: [TEST_BUG] Test java/awt/Frame/MiscUndecorated/RepaintTest.java fails
  • 5e98f99: 8276800: Fix table headers in NumericShaper.html
  • 2ca4ff8: 8244202: Implementation of JEP 418: Internet-Address Resolution SPI
  • c29cab8: 8276112: Inconsistent scalar replacement debug info at safepoints

Your commit was automatically rebased without conflicts.

@openjdk openjdk bot closed this Nov 12, 2021
@openjdk openjdk bot added integrated and removed ready rfr labels Nov 12, 2021
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@openjdk openjdk bot commented Nov 12, 2021

@pliden Pushed as commit 6b833db.

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

@pliden pliden deleted the 8275329_zgc_too_many_phases branch Nov 15, 2021
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