[GitHub] [pulsar] codelipenghui commented on a change in pull request #12654: Remove unused listeners if it have no listeners.

[GitBox <gi...@apache.org>]

codelipenghui commented on a change in pull request #12654:
URL: https://github.com/apache/pulsar/pull/12654#discussion_r744478204



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File path: pulsar-broker/src/main/java/org/apache/pulsar/broker/service/SystemTopicBasedTopicPoliciesService.java
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@@ -474,7 +475,13 @@ public void registerListener(TopicName topicName, TopicPolicyListener<TopicPolic
 
     @Override
     public void unregisterListener(TopicName topicName, TopicPolicyListener<TopicPolicies> listener) {
-        listeners.computeIfAbsent(topicName, k -> Lists.newCopyOnWriteArrayList()).remove(listener);

Review comment:
       It should be a problem if thread A reaches line 478 first, then thread B reaches line 473 and then add a listener. After that, thread A continues to remove the listener, finally, the added listener will be removed, but actually, the `unregisterListener` operation happens first, we will get unexpected behavior.




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