[PR] Optimize reactor sort, model pool, and phase comparator performance [maven]

["gnodet (via GitHub)" <gi...@apache.org>]

gnodet opened a new pull request, #12652:
URL: https://github.com/apache/maven/pull/12652

   ## Summary
   
   JFR profiling of a 4,383-module reactor build revealed three hotspots that together consume ~35% of CPU time. All three share the same root cause: **O(n) linear scans used inside tight loops or comparators**.
   
   ### Fixes
   
   - **`DefaultGraphBuilder`** (23.5% CPU): Three call sites use `result.sort(comparing(sortedProjects::indexOf))` where `ArrayList.indexOf()` is O(n), causing **O(n² log n)** total `MavenProject.equals()` calls (~230M for 4,383 modules). Replaced with a `HashMap<MavenProject, Integer>` index built in O(n), reducing each sort comparison to O(1).
   
   - **`DefaultModelObjectPool`** (~8% CPU, ~2.4 GB allocation pressure):
     - `getPooledTypes()` re-parses a comma-separated property string into a new `Stream` → `Set` **on every `process()` call** (hundreds of thousands of times). Cached at construction time.
     - `PoolKey.dependencyHashCode()` uses `Objects.hash()` with 12 arguments, allocating a `new Object[12]` on every call. Inlined the hash computation.
     - Added hashCode fast-rejection to `PoolKey.equals()` to skip expensive deep equality when hashes differ.
   
   - **`PhaseComparator`** (~2% CPU): `List.indexOf()` in `compare()` is O(n) per call. Pre-built a `HashMap<String, Integer>` in the constructor for O(1) phase index lookups.
   
   ### JFR Profile (before these fixes)
   
   | Rank | Method | CPU % | Root Cause |
   |------|--------|------:|------------|
   | 1 | `MavenProject.equals` | 23.5% | Called from `ArrayList.indexOf` in `DefaultGraphBuilder` sort |
   | 2 | `DefaultModelObjectPool$PoolKey.*` | ~8% | Stream re-parse + `Objects.hash` varargs |
   | 3 | `DefaultDependencyManagementImporter.importManagement` | 5.8% | (not addressed — model-level, not a data-structure issue) |
   | 4 | `PhaseComparator.compare` | ~2% | `List.indexOf` per comparison |
   
   ### Complexity reduction
   
   | Component | Before | After |
   |-----------|--------|-------|
   | `DefaultGraphBuilder` sort | O(n² log n) | O(n log n) |
   | `DefaultModelObjectPool.process()` | O(k) stream + alloc per call | O(1) Set.contains |
   | `PoolKey.dependencyHashCode` | 1 Object[12] alloc per call | 0 allocations |
   | `PhaseComparator.compare` | O(n) per comparison | O(1) per comparison |
   
   ## Test plan
   
   - [x] `DefaultModelObjectPoolTest` passes
   - [x] Full `maven-impl` test suite passes
   - [ ] `DefaultGraphBuilderTest` (blocked by pre-existing `ProjectBuildLogAppender` compile error on master — unrelated to this PR)
   - [ ] CI validation
   
   🤖 Generated with [Claude Code](https://claude.com/claude-code)


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Re: [PR] Optimize reactor sort, model pool, and phase comparator performance [maven]

["gnodet (via GitHub)" <gi...@apache.org>]

gnodet merged PR #12652:
URL: https://github.com/apache/maven/pull/12652


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