[GitHub] [kafka] chia7712 commented on a change in pull request #8657: KAFKA-8334 Make sure the thread which tries to complete delayed reque…

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chia7712 commented on a change in pull request #8657:
URL: https://github.com/apache/kafka/pull/8657#discussion_r482743072



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File path: core/src/test/scala/unit/kafka/coordinator/AbstractCoordinatorConcurrencyTest.scala
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@@ -201,8 +201,8 @@ object AbstractCoordinatorConcurrencyTest {
         }
       }
       val producerRequestKeys = entriesPerPartition.keys.map(TopicPartitionOperationKey(_)).toSeq
-      watchKeys ++= producerRequestKeys
       producePurgatory.tryCompleteElseWatch(delayedProduce, producerRequestKeys)
+      watchKeys ++= producerRequestKeys

Review comment:
       @junrao This change avoids deadlock in ```TransactionCoordinatorConcurrencyTest```.
   
   If we update ```watchKeys``` before ```tryCompleteElseWatch```, the other threads can take the same key to complete delayed request.  Hence the deadlock happens due to following conditions.
   
   **thread_1**  holds ```stateLock``` of TransactionStateManager to call ```appendRecords``` and it requires lock of delayed request to call ```tryCompleteElseWatch```.
   
   **thread_2** holds lock of delayed request to call ```onComplete``` (updateCacheCallback) and ```updateCacheCallback``` requires ```stateLock``` of TransactionStateManager.




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