[jira] [Commented] (KAFKA-5395) Distributed Herder Deadlocks on Shutdown

["Michael Jaschob (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-5395?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16040257#comment-16040257 ] 

Michael Jaschob commented on KAFKA-5395:
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Probably didn't mean to synchronize the public [close|https://github.com/apache/kafka/blob/0.10.2.1/clients/src/main/java/org/apache/kafka/clients/consumer/internals/AbstractCoordinator.java#L664] method. Think removing synchronization there would fix this (the protected version synchronizes after the heartbeat thread has joined).

> Distributed Herder Deadlocks on Shutdown
> ----------------------------------------
>
>                 Key: KAFKA-5395
>                 URL: https://issues.apache.org/jira/browse/KAFKA-5395
>             Project: Kafka
>          Issue Type: Bug
>          Components: KafkaConnect
>    Affects Versions: 0.10.2.1
>            Reporter: Michael Jaschob
>         Attachments: connect_01021_shutdown_deadlock.txt
>
>
> We're trying to upgrade Kafka Connect to 0.10.2.1 and see that the process does not shut down cleanly. It hangs instead. From what I can tell [KAFKA-4786|https://github.com/apache/kafka/commit/ba4eafa7874988374abcd9f48fbab96abb2032a4] introduced this deadlock.
> [close|https://github.com/apache/kafka/blob/0.10.2.1/clients/src/main/java/org/apache/kafka/clients/consumer/internals/AbstractCoordinator.java#L664] on the AbstractCoordinator is marked as synchronized and acquires the coordinator's monitor. The first thing it tries to do is [join|https://github.com/apache/kafka/blob/0.10.2.1/clients/src/main/java/org/apache/kafka/clients/consumer/internals/AbstractCoordinator.java#L323] the heartbeat thread.
> Meanwhile, the heartbeat thread is [synchronized on the same monitor|https://github.com/apache/kafka/blob/0.10.2.1/clients/src/main/java/org/apache/kafka/clients/consumer/internals/AbstractCoordinator.java#L891], which it relinquishes when it [waits|https://github.com/apache/kafka/blob/0.10.2.1/clients/src/main/java/org/apache/kafka/clients/consumer/internals/AbstractCoordinator.java#L926]. But for the wait to return (and the run method of the heartbeat to terminate) it needs to reacquire that monitor.
> There's no way for the heartbeat thread to reacquire the monitor since it is held by the distributed herder thread. And the distributed herder will never relinquish the monitor since it is waiting for the heartbeat thread to join.
> I am attaching a thread dump illustrating the situation. Take note in particular of threads #178 (the heartbeat thread) and #159 (the herder thread). The former is BLOCKED trying to reacquire 0x00000007406cc0c0, and the latter is WAITING on the heartbeat thread to join, having itself acquired 0x00000007406cc0c0.



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