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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