gen-z support in GCToolKit

Integrate gen-z work into GCToolKit and any supporting classes that may need to know about this collector. Much of this work is yet to be defined.

[brunoborges]

/relevance-check

[github-actions]

Relevance Assessment: Likely Outdated

• Summary: The core generational ZGC support requested in this issue has been implemented across multiple PRs merged between February and September 2025. Remaining gaps are tracked by separate, more specific issues.

• Evidence:

  • PR ZGC Generational Support #414 ("ZGC Generational Support") was merged on Feb 25, 2025 — added the foundational generational ZGC parsing, new event types (ZGCYoungCollection, ZGCOldCollection), the GENERATIONAL_ZGC diary flag, and parser logic to distinguish generational vs. legacy ZGC. (2,164 additions across 31 files)
  • PR [ZGC] Add support for heap capacity, nMethod and relocation summary #426 ("[ZGC] Add support for heap capacity, nMethod and relocation summary") was merged Apr 10, 2025 — added more generational ZGC data parsing for heap capacity, nMethod tracking, and relocation/age table information.
  • PR Report ZGC individual collections instead of cycles (#445) #447 ("Report ZGC individual collections instead of cycles") was merged Jun 23, 2025 — major refactoring to correctly handle concurrent generational ZGC collections, fixing issues where data was lost when minor cycles overlapped major cycles.
  • PR Fix "No Detail" Use Cases for Legacy and Generational ZGC logging #448 ("Fix 'No Detail' Use Cases for Legacy and Generational ZGC logging") was merged Sep 10, 2025 — fixed edge cases for logs without detailed output.
  • The codebase now contains: GenZPatterns.java, generational branching in ZGCParser.java (diary.isGenerationalZGC()), event types ZGCYoungCollection and ZGCOldCollection, comprehensive test coverage in GenerationalZGCParserTest.java, and the GENERATIONAL_ZGC flag in SupportedFlags.java and Diary.java.
  • Remaining ZGC work is tracked by more specific open issues: ZGC parsing refactoring #439 (ZGC parsing refactoring / DRY + thread counts), ZGC missing data #381 (ZGC missing data — safepoints, mark summary, references, etc.), and ZGC events GarbageCollectionType comes "Unknown" #380 (ZGC GarbageCollectionType reported as "Unknown").

• Recommendation: 🗄️ Consider closing — The generational ZGC integration described in this issue ("Integrate gen-z work into GCToolKit and any supporting classes") has been substantially completed through PRs ZGC Generational Support #414, [ZGC] Add support for heap capacity, nMethod and relocation summary #426, Report ZGC individual collections instead of cycles (#445) #447, and Fix "No Detail" Use Cases for Legacy and Generational ZGC logging #448. The remaining work items are narrower in scope and already tracked by dedicated issues (ZGC parsing refactoring #439, ZGC missing data #381, ZGC events GarbageCollectionType comes "Unknown" #380). Keeping this broad issue open adds little value since the actionable work is better captured elsewhere.

Generated by Relevance Check Agent for issue #280