LiamClarkeNZ commented on a change in pull request #11920:
URL: https://github.com/apache/kafka/pull/11920#discussion_r833080985
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File path: core/src/main/scala/kafka/server/DynamicBrokerConfig.scala
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@@ -201,7 +202,9 @@ class DynamicBrokerConfig(private val kafkaConfig:
KafkaConfig) extends Logging
private[server] val staticDefaultConfigs =
ConfigDef.convertToStringMapWithPasswordValues(KafkaConfig.defaultValues.asJava).asScala
private val dynamicBrokerConfigs = mutable.Map[String, String]()
private val dynamicDefaultConfigs = mutable.Map[String, String]()
- private val reconfigurables = mutable.Buffer[Reconfigurable]()
+
+ // Use COWArrayList to prevent concurrent modification exception when
reconfigurable added while iteration over list occurring
+ private val reconfigurables = new CopyOnWriteArrayList[Reconfigurable]()
private val brokerReconfigurables = mutable.Buffer[BrokerReconfigurable]()
Review comment:
That's a good question. I am happy to do so, I don't have much
experience in this area of code, I just wanted to help eliminate some flaky
tests, but I can't see any downsides to doing so.
I chose to use a `CopyOnWriteArrayList` because iteration over the
reconfigurables is a lot more common than adding items, so the overhead is
cheap.
I also looked at a `ConcurrentQueue`, as that also avoids the concurrent
modification exception, and is cheaper to add items to.
I chose the COWArrayList because iteration over a ConcurrentQueue one is
non-deterministic - i.e., a freshly added Reconfigurable could appear in an
iteration that's currently occurring, and I could envisage a bunch of subtle
ways that could maybe cause issues.
Whereas the CopyOnWriteArrayList offers deterministic iteration, which feels
safer. But there's some additional cost on adding items to the
brokerReconfigurables.
If that cost is acceptable, and people are happy for me to defensively
extend the change to the brokerReconfigurables also, I'd be pleased to do so :)
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