G1 Concurrent undo cycle event

New G1 concurrent event that needs to be wired into GCToolkit. Implementation has been started

[brunoborges]

/relevance-check

[github-actions]

Relevance Assessment: Still Relevant

• Summary: The G1 Concurrent Undo Cycle event has a partial implementation in place, but the work is explicitly marked as incomplete with multiple TODO comments indicating it needs to be finished in a future PR.

• Evidence:

  • ✅ The G1ConcurrentUndoCycle event class exists in api/.../event/g1gc/G1ConcurrentUndoCycle.java
  • ✅ The GarbageCollectionTypes.G1GCConcurrentUndoCycle enum entry exists (line 46)
  • ✅ Parse rules CONCURRENT_UNDO_CYCLE_START and CONCURRENT_UNDO_CYCLE_END are defined in UnifiedG1GCPatterns.java
  • ✅ Parser methods and publish logic exist in UnifiedG1GCParser.java
  • ⚠️ TODO on line 574: //todo: ????? this is a different type of concurrent cycle
  • ⚠️ TODO on line 580: //todo: need support for JDK 17 undo concurrent cycle event.. started here, commented out for a future PR.
  • ⚠️ buildEvent() returns null for this case (G1GCForwardReference.java line 762-767) with comment: "This event will be filled in a future PR."
  • 🐛 Possible bug in G1ConcurrentUndoCycle.java line 17: the second constructor passes GarbageCollectionTypes.G1GCConcurrentCleanup instead of G1GCConcurrentUndoCycle
  • No related PRs have been submitted to complete this work

• Recommendation: ✅ Keep open — The scaffolding is in place, but the implementation is explicitly incomplete with TODO markers awaiting a future PR. The buildEvent() method returns null for this event type, and the TODO comments from the original author confirm more work is needed. The issue was filed by a now-deleted user account, so it may benefit from additional context or acceptance criteria from current maintainers.

Generated by Relevance Check Agent for issue #186