[ISSUE #11080] Skip unused remoting client event executor

[qianye1001]

Which Issue(s) This PR Fixes

Fixes #11080

Brief Description

NettyRemotingClient.start() starts a NettyEventExecutor even when no ChannelEventListener is configured. Since connection handlers already skip event submission in that case, each such client keeps an unused thread polling an empty queue every three seconds. This includes internal clients built through MQClientAPIExt.

Start the executor only when channelEventListener != null. Clients with a listener retain their existing event dispatch behavior. The existing shutdown implementation safely handles an executor that was never started.

How Did You Test This Change?

Added regression tests covering startup and shutdown without an event thread when no listener is configured, and ACTIVE event delivery plus thread termination when a listener is configured.

Passed on JDK 11:

mvn -B -pl remoting -am -Dtest=NettyRemotingClientTest -Dsurefire.failIfNoSpecifiedTests=false test

All 16 tests passed, including the two new tests. Checkstyle and SpotBugs also passed.

[RockteMQ-AI]

Summary

Clean optimization — skip starting NettyEventExecutor when no ChannelEventListener is configured. The executor thread was polling an empty queue every 3 seconds for nothing, so this saves one thread per client instance that doesn't need channel event callbacks.

Review

• Correctness ✅ — The guard is safe: channelEventListener is set in the constructor and effectively final. Connection handlers already skip event submission when the listener is null, so the executor was indeed doing nothing.
• Tests ✅ — Good coverage of both paths (with/without listener). The reflection-based thread state verification is a pragmatic choice for lifecycle testing.
• Performance ✅ — Eliminates unnecessary thread creation and periodic wake-ups. Minor but meaningful for deployments with many client instances.
• Compatibility ✅ — No API changes, purely internal optimization.

LGTM.

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Automated review by github-manager-bot

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 48.89%. Comparing base (4fd0e3b) to head (811c92d).

Additional details and impacted files

@@              Coverage Diff              @@
##             develop   #11081      +/-   ##
=============================================
- Coverage      48.92%   48.89%   -0.04%     
+ Complexity     13846    13837       -9     
=============================================
  Files           1382     1382              
  Lines         101602   101603       +1     
  Branches       13213    13214       +1     
=============================================
- Hits           49709    49678      -31     
- Misses         45866    45882      +16     
- Partials        6027     6043      +16     

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