mumrah commented on a change in pull request #10008:
URL: https://github.com/apache/kafka/pull/10008#discussion_r568149064
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File path:
core/src/main/scala/kafka/coordinator/group/GroupMetadataManager.scala
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@@ -78,7 +78,20 @@ class GroupMetadataManager(brokerId: Int,
private val shuttingDown = new AtomicBoolean(false)
/* number of partitions for the consumer metadata topic */
- private val groupMetadataTopicPartitionCount =
getGroupMetadataTopicPartitionCount
+ private var _groupMetadataTopicPartitionCount: Option[Int] = Option.empty //
lazy, once-only evaluation
+ private def groupMetadataTopicPartitionCount: Int = {
+ _groupMetadataTopicPartitionCount match {
+ case Some(partitionCount) => partitionCount
+ case None => synchronized { // make sure we only invoke the function once
+ _groupMetadataTopicPartitionCount match {
+ case Some(partitionCount) => partitionCount // another thread beat
us to it
+ case None =>
+ _groupMetadataTopicPartitionCount =
Some(offsetsTopicPartitionCountFunc())
Review comment:
It's worth noting that if our underlying function throws an error, this
will throw as well for any usages of `groupMetadataTopicPartitionCount` (e.g.,
`GroupMetadataManager#partitionFor`). That wasn't possible in the ZK world
(since this value was cached on startup), so we should probably make sure the
callers can all tolerate an exception.
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