refactor: throw exception in registerConsumer + lock-free StoreStatsService

[juincen]

Changes

1. registerConsumer: throw MQClientException instead of returning boolean

Move the duplicate-group exception throwing from callers into MQClientInstance.registerConsumer() itself, removing redundant if (!registerOK) throw checks in all three consumer implementations.

• MQClientInstance.java - throw exception instead of returning false
• DefaultMQPushConsumerImpl.java - remove redundant check
• DefaultMQPullConsumerImpl.java - remove redundant check
• DefaultLitePullConsumerImpl.java - remove redundant check

2. StoreStatsService: lock-free AtomicLong for max tracking

Replace volatile long + ReentrantLock with AtomicLong.accumulateAndGet() for thread-safe max-value tracking on the hot message path.

• putMessageEntireTimeMax / getMessageEntireTimeMax — eliminate lock contention in hot put/get path
• dispatchMaxBuffer — fix TOCTOU race condition in volatile read-modify-write
• toString() — chained StringBuilder.append() instead of string concatenation

[RockteMQ-AI]

Summary

Two clean improvements: (1) moves duplicate-group exception throwing into registerConsumer() itself, eliminating redundant throw-after-check patterns in all three consumer implementations; (2) replaces volatile long + ReentrantLock with AtomicLong.accumulateAndGet(Math::max) in StoreStatsService for lock-free max tracking.

Findings

• [Info] DefaultMQPushConsumerImpl.java — The original code called consumeMessageService.shutdown() in the registration-failed error path before throwing. The refactored version removes this since the exception is now thrown inside registerConsumer() before any service state changes. This is correct behavior (the service was never started), but worth confirming that no caller depends on the shutdown side-effect.
• [Info] StoreStatsService.java:73 — AtomicLong.accumulateAndGet with Math::max is a good lock-free replacement. Note that under high contention this may spin, but for a stats counter the contention should be low.

LGTM.

---

Automated review by github-manager-bot