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

[pliden]

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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Issue

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

Reviewers

• Stefan Karlsson (@stefank - Reviewer)
• Erik Österlund (@fisk - Reviewer)

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

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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

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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

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Thanks for reviewing!

/integrate

[openjdk]

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]

@pliden Pushed as commit 6b833db.

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