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From Ewen Cheslack-Postava <e...@confluent.io>
Subject Re: Hung Kafka Threads?
Date Tue, 14 Apr 2015 05:28:29 GMT
"Parking to wait for" just means the thread has been put to sleep while
waiting for some synchronized resource. In this case, "ConditionObject"
indicates it's probably await()ing on a condition variable. This almost
always means that thread is just waiting for notification from another
thread that there's something to do (AbstractQueuedSynchronizer is a
generic low-level synchronization utility and used for things like
BlockingQueues). The only way it would be hung in this condition is if no
other thread will ever wake it up (e.g. due to some deadlock, the thread it
relies on to wake it up dies, etc.)

With just the line given, you can't tell exactly what's going on, but
brokers especially may use very little CPU since most of what they do is
IO. Seeing these lines in a thread dump is completely normal since there
will often be threads just waiting for new work to do, so they shouldn't
worry you unless you have other reason to believe something is wrong.

On Mon, Apr 13, 2015 at 9:19 PM, Sharma, Prashant <psharma@netsuite.com>

>  Kafka version is On taking a thread dump against one of our
> servers in Kafka Cluster, i see lot of threads with message below:
> "SOMEID-9" id=67784 idx=0x75c tid=24485 prio=5 alive, parked,
> native_blocked, daemon
>     -- Parking to wait for:
> java/util/concurrent/locks/AbstractQueuedSynchronizer$ConditionObject@0x100a13500
>     at jrockit/vm/Locks.park0(J)V(Native Method)
> There are multiple threads with the message “Parking to wait for” with the
> same objectId- 0x100a13500.
> Does this imply that the consumer threads are  stuck or  just sitting
> idle?
> Thanks,
> Prashant
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