[hehuang139]

What is the purpose of the change?

Fixes #16149.

A metadata retry holds the instance listener monitor while fetching metadata from providers. If that request stalls, registry callbacks cannot update the provider list and subsequent retries continue using obsolete instances.

Update instance lists under a short synchronized section and let one refresh processor retrieve metadata from a snapshot. Notifications received during retrieval update the latest snapshot and return; obsolete results are discarded before address publication. Pending changes are also processed after a retrieval failure. Destroyed listeners reject late results and release queued instance events, including when destruction races with the next refresh iteration.

Validation on Linux with JDK 17 and Maven 3.9.9:

• Reproduced the issue before the fix: a provider-change callback timed out while a retry metadata fetch was paused.
• Passed 39 tests covering concurrent provider changes, obsolete snapshots with multiple revisions, repeated notification failures, event acceptance, destruction, existing listeners with both empty-protection settings, and service discovery registry behavior.
• Passed module spotless:check and git diff --check.

The test command was:

mvn -B -ntp -pl dubbo-registry/dubbo-registry-api -am test jacoco:report -Dtest=ServiceInstancesChangedListenerConcurrencyTest,ServiceInstancesChangedListenerTest,ServiceInstancesChangedListenerWithoutEmptyProtectTest,ServiceDiscoveryRegistryTest -Dsurefire.failIfNoSpecifiedTests=false -DfailIfNoTests=false -Pjacoco,skip-spotless -Dcheckstyle.skip=true -Drat.skip=true

Checklist

• Make sure there is a GitHub_issue field for the change.
• Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
• Write necessary unit-test to verify your logic correction.
• Make sure GitHub Actions can pass.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 90.74074% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 60.94%. Comparing base (b73b9d1) to head (1db131f).

Files with missing lines	Patch %	Lines
...vent/listener/ServiceInstancesChangedListener.java	90.74%	2 Missing and 3 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                3.3   #16522      +/-   ##
============================================
+ Coverage     60.89%   60.94%   +0.05%     
- Complexity    11753    11770      +17     
============================================
  Files          1953     1953              
  Lines         89278    89324      +46     
  Branches      13475    13485      +10     
============================================
+ Hits          54367    54440      +73     
+ Misses        29329    29305      -24     
+ Partials       5582     5579       -3     

Flag	Coverage Δ
integration-tests-java21	32.16% <64.81%> (+0.08%)	⬆️
integration-tests-java8	32.22% <64.81%> (+0.03%)	⬆️
samples-tests-java21	32.14% <55.55%> (+<0.01%)	⬆️
samples-tests-java8	29.75% <55.55%> (+<0.01%)	⬆️
unit-tests-java11	59.18% <90.74%> (+0.05%)	⬆️
unit-tests-java17	?
unit-tests-java21	58.67% <90.74%> (+0.06%)	⬆️
unit-tests-java25	58.62% <90.74%> (+0.05%)	⬆️
unit-tests-java8	59.20% <90.74%> (+0.02%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ 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.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[hehuang139]

Added follow-up coverage in 1db131f for repeated notification failures, obsolete multi-revision snapshots, ignored events, and destruction during refresh. Reviewing destruction also found a queued event that stayed referenced after the listener was destroyed. The listener now releases that event and safely stops before taking another snapshot.

The focused listener/registry run passes all 39 tests on Linux with JDK 17. Both Spotless and the diff checks pass. The five lines previously reported as missing by Codecov are exercised by the new tests; CI will validate the updated commit.