poorbarcode commented on code in PR #23795:
URL: https://github.com/apache/pulsar/pull/23795#discussion_r1901421451
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pulsar-broker/src/main/java/org/apache/pulsar/broker/service/persistent/PersistentStickyKeyDispatcherMultipleConsumersClassic.java:
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@@ -560,8 +593,11 @@ public boolean hasSameKeySharedPolicy(KeySharedMeta ksm) {
&& ksm.isAllowOutOfOrderDelivery() ==
this.allowOutOfOrderDelivery);
}
- public LinkedHashMap<Consumer, Position> getRecentlyJoinedConsumers() {
- return recentlyJoinedConsumers;
+ public synchronized LinkedHashMap<Consumer, Position>
getRecentlyJoinedConsumers() {
+ if (recentlyJoinedConsumers == null) {
+ return null;
+ }
+ return new LinkedHashMap<>(recentlyJoinedConsumers);
Review Comment:
> We should return a unmodified map instead of a new copy of the map?
No, the thread that gets the unmodified map may encounter a
`ConcurrentModificationException`, see following case:
- `thread-1`: get an unmodified map
- call `map.foreach`
- `thread-2`: get the lock and remove an item from the map.
- `thread-1` will get a `ConcurrentModificationException` because its
`foreach` is in progress
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