[ISSUE #10892] Tolerate concurrent topic cache eviction

[Aias00]

Closes #10892.

Summary

• select a candidate topic through a single iterator in both the Java producer and Proxy route service
• avoid the check-then-iterate race when concurrent cache eviction removes the final entry
• add deterministic regression tests for both affected paths

Tests

• JAVA_HOME=$(/usr/libexec/java_home -v 1.8) PATH="$JAVA_HOME/bin:$PATH" mvn -q -pl client -am -Dtest=DefaultMQProducerImplTest -DfailIfNoTests=false test
• JAVA_HOME=$(/usr/libexec/java_home -v 1.8) PATH="$JAVA_HOME/bin:$PATH" mvn -q -pl proxy -am -Dtest=ClusterTopicRouteServiceTest,LocalTopicRouteServiceTest -DfailIfNoTests=false test

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.

[RockteMQ-AI]

Summary

This PR fixes a real race condition in pickTopic() across both the Java producer (DefaultMQProducerImpl) and Proxy route service (TopicRouteService).

The original code had a check-then-act gap: isEmpty() returns false, but before keySet().iterator().next() executes, a concurrent cache eviction could remove the last entry, causing NoSuchElementException. The fix correctly replaces the two-step check with a single iterator: iterator.hasNext() + iterator.next(), which is safe under ConcurrentHashMap's weakly consistent iteration semantics.

Verdict: LGTM — clean, minimal, well-tested fix.

Findings

• [Info] client/.../DefaultMQProducerImpl.java:182 — The ClearingConcurrentMap test helper is duplicated in both DefaultMQProducerImplTest and ClusterTopicRouteServiceTest. Consider extracting to a shared test utility if similar patterns emerge in the future. Minor, not blocking.

---

Automated review by "github-manager-bot"

[codecov-commenter]

Codecov Report

❌ Patch coverage is 66.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 48.51%. Comparing base (293f588) to head (e9587aa).

Files with missing lines	Patch %	Lines
...mq/client/impl/producer/DefaultMQProducerImpl.java	66.66%	0 Missing and 1 partial ⚠️
...ocketmq/proxy/service/route/TopicRouteService.java	66.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             develop   #10893      +/-   ##
=============================================
- Coverage      48.60%   48.51%   -0.09%     
+ Complexity     13690    13655      -35     
=============================================
  Files           1381     1381              
  Lines         101464   101466       +2     
  Branches       13187    13189       +2     
=============================================
- Hits           49318    49230      -88     
- Misses         46158    46223      +65     
- Partials        5988     6013      +25     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[RockteMQ-AI]

Summary

Fixes race condition in topic cache eviction by using single iterator. Good defensive fix with regression tests.

LGTM.

---

Automated review by github-manager-bot

[Aias00]

Rebased onto current develop and revalidated DefaultMQProducerImplTest plus ClusterTopicRouteServiceTest. The previous Bazel failure was PopPriorityIT, an unrelated integration test; the branch update will trigger a fresh CI run.