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https://issues.apache.org/jira/browse/KAFKA-2168?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14582524#comment-14582524
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Jason Gustafson commented on KAFKA-2168:
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Updated reviewboard https://reviews.apache.org/r/34789/diff/
against branch upstream/trunk
> New consumer poll() can block other calls like position(), commit(), and
> close() indefinitely
> ---------------------------------------------------------------------------------------------
>
> Key: KAFKA-2168
> URL: https://issues.apache.org/jira/browse/KAFKA-2168
> Project: Kafka
> Issue Type: Bug
> Components: clients, consumer
> Reporter: Ewen Cheslack-Postava
> Assignee: Jason Gustafson
> Attachments: KAFKA-2168.patch, KAFKA-2168_2015-06-01_16:03:38.patch,
> KAFKA-2168_2015-06-02_17:09:37.patch, KAFKA-2168_2015-06-03_18:20:23.patch,
> KAFKA-2168_2015-06-03_21:06:42.patch, KAFKA-2168_2015-06-04_14:36:04.patch,
> KAFKA-2168_2015-06-05_12:01:28.patch, KAFKA-2168_2015-06-05_12:44:48.patch,
> KAFKA-2168_2015-06-11_14:09:59.patch
>
>
> The new consumer is currently using very coarse-grained synchronization. For
> most methods this isn't a problem since they finish quickly once the lock is
> acquired, but poll() might run for a long time (and commonly will since
> polling with long timeouts is a normal use case). This means any operations
> invoked from another thread may block until the poll() call completes.
> Some example use cases where this can be a problem:
> * A shutdown hook is registered to trigger shutdown and invokes close(). It
> gets invoked from another thread and blocks indefinitely.
> * User wants to manage offset commit themselves in a background thread. If
> the commit policy is not purely time based, it's not currently possibly to
> make sure the call to commit() will be processed promptly.
> Two possible solutions to this:
> 1. Make sure a lock is not held during the actual select call. Since we have
> multiple layers (KafkaConsumer -> NetworkClient -> Selector -> nio Selector)
> this is probably hard to make work cleanly since locking is currently only
> performed at the KafkaConsumer level and we'd want it unlocked around a
> single line of code in Selector.
> 2. Wake up the selector before synchronizing for certain operations. This
> would require some additional coordination to make sure the caller of
> wakeup() is able to acquire the lock promptly (instead of, e.g., the poll()
> thread being woken up and then promptly reacquiring the lock with a
> subsequent long poll() call).
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