balodesecurity opened a new pull request, #8325:
URL: https://github.com/apache/hadoop/pull/8325
## Summary
`ExcessRedundancyMap` uses a single coarse-grained `synchronized` monitor
for all operations. Because `contains()`, `getSize4Testing()`, and
`getExcessRedundancyMap()` are purely read-only, they unnecessarily serialize
against each other under the block management write lock, reducing throughput
on read-heavy workloads.
### Changes
- Replace `synchronized` on every method with an explicit
`ReentrantReadWriteLock`:
- **Read lock**: `contains()`, `getSize4Testing()`,
`getExcessRedundancyMap()`
- **Write lock**: `add()`, `remove()`, `clear()`
- The `size` counter is already an `AtomicLong` and requires no additional
locking.
### Test
Added `TestExcessRedundancyMap` with 4 unit tests:
- `testAddContainsRemove` — basic correctness of add/contains/remove
- `testClear` — clear resets map and size counter
- `testConcurrentReads` — 8 concurrent readers all complete within 10 s (no
deadlock)
- `testConcurrentWritesProduceCorrectSize` — 10 concurrent writers produce a
consistent final size
All 4 tests pass.
## Test plan
- [x] `TestExcessRedundancyMap` (4 tests) — PASS
- [ ] Full `blockmanagement` test suite (CI)
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