8355789: GenShen: assert(_degen_point == ShenandoahGC::_degenerated_unset) failed: Should not be set yet: Outside of Cycle

[earthling-amzn]

When old generation marking is cancelled to run a young collection. we still set a _degen_point for reasons that became vestigial after JDK-8349094. When old marking is cancelled, the _degen_point should only be set if the marking was cancelled because of an allocation failure (and it should still only be set to "outside of cycle"). The following sequence could lead to this assertion failure:

1. Control thread is marking old
2. Young GC preempts it
3. Control thread sets the degen point because the old GC was "cancelled"
4. The concurrent young GC fails and attempts to set a degenerated point
5. This trips the assert because we already (incorrectly) set the degen point in 3.

---

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Issue

• JDK-8355789: GenShen: assert(_degen_point == ShenandoahGC::_degenerated_unset) failed: Should not be set yet: Outside of Cycle (Bug - P4)

Reviewers

• Kelvin Nilsen (@kdnilsen - Committer)
• Y. Srinivas Ramakrishna (@ysramakrishna - Reviewer)

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[bridgekeeper]

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[openjdk]

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

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

8355789: GenShen: assert(_degen_point == ShenandoahGC::_degenerated_unset) failed: Should not be set yet: Outside of Cycle

Reviewed-by: kdnilsen, ysr

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At the time when this comment was updated there had been 21 new commits pushed to the master branch:

• 8b16897: 8355262: Test sun/security/ssl/SSLSessionImpl/NoInvalidateSocketException.java failed: accept timed out
• bf52eb0: 8355632: WhiteBox.waitForReferenceProcessing() fails assert for return type
• c2485d5: 8351113: RC2ParameterSpec throws IllegalArgumentException when offset is negative
• ... and 18 more: https://git.openjdk.org/jdk/compare/1fd136cd6b863ebee70e42b2966584218d0919ec...master

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[openjdk]

@earthling-amzn The following labels will be automatically applied to this pull request:

• hotspot-gc
• shenandoah

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[mlbridge]

Webrevs

• 00: Full (7071fdf3)

[ysramakrishna]

This looks fine, but it also leaves me with the feeling that we should sit down and review the interaction of the state machines for the young and old collections with the mutator allocations, and see if we can simplify the interaction protocol.

🚢

[earthling-amzn]

/integrate

[openjdk]

Going to push as commit 5e27547.
Since your change was applied there have been 22 commits pushed to the master branch:

• 6850757: 8355689: Wrong native entry name for FloatMaxVector vector math stubs with -XX:MaxVectorSize=8
• 8b16897: 8355262: Test sun/security/ssl/SSLSessionImpl/NoInvalidateSocketException.java failed: accept timed out
• bf52eb0: 8355632: WhiteBox.waitForReferenceProcessing() fails assert for return type
• ... and 19 more: https://git.openjdk.org/jdk/compare/1fd136cd6b863ebee70e42b2966584218d0919ec...master

Your commit was automatically rebased without conflicts.

[openjdk]

@earthling-amzn Pushed as commit 5e27547.

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