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https://issues.apache.org/jira/browse/AVRO-747?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13054746#comment-13054746
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James Baldassari commented on AVRO-747:
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As of AVRO-539, CallFuture no longer contains a Semaphore. However, I think
this enhancement still applies. If the transceiver is explicitly closed (as
opposed to the connection being lost for some other reason), any pending
requests should be canceled. I should be able to roll this behavior into the
patch I just submitted for AVRO-842.
> NettyTransceiver: release semaphores on close so that clients are not blocked.
> ------------------------------------------------------------------------------
>
> Key: AVRO-747
> URL: https://issues.apache.org/jira/browse/AVRO-747
> Project: Avro
> Issue Type: Improvement
> Components: java
> Affects Versions: 1.5.0
> Reporter: Bruno Dumon
> Assignee: Bruno Dumon
> Fix For: 1.5.2
>
> Attachments: avro-747v2-patch.txt,
> netty-transceiver-release-semaphores-on-close-patch.txt
>
>
> I use Avro RPC with the NettyTransceiver.
> When I kill the server, often the client hangs, jstack shows the following:
> {noformat}
> "pool-6-thread-1" prio=10 tid=0x09fef000 nid=0x3382 waiting on condition
> [0x76fc7000]
> java.lang.Thread.State: WAITING (parking)
> at sun.misc.Unsafe.park(Native Method)
> - parking to wait for <0xa1df2e40> (a
> java.util.concurrent.Semaphore$NonfairSync)
> at java.util.concurrent.locks.LockSupport.park(LockSupport.java:158)
> at
> java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:811)
> at
> java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireSharedInterruptibly(AbstractQueuedSynchronizer.java:969)
> at
> java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireSharedInterruptibly(AbstractQueuedSynchronizer.java:1281)
> at java.util.concurrent.Semaphore.acquire(Semaphore.java:286)
> at
> org.apache.avro.ipc.NettyTransceiver$CallFuture.get(NettyTransceiver.java:207)
> at
> org.apache.avro.ipc.NettyTransceiver.transceive(NettyTransceiver.java:137)
> at org.apache.avro.ipc.Requestor.request(Requestor.java:123)
> - locked <0xa20986c0> (a org.apache.avro.specific.SpecificRequestor)
> at
> org.apache.avro.specific.SpecificRequestor.invoke(SpecificRequestor.java:52)
> ...
> {noformat}
> Not that this matters much, but the client application is written such that
> it discovers the available servers via ZooKeeper. When a server disappears,
> it calls close on the corresponding NettyTransceiver.
> I have adjusted the NettyTransceiver.close() method to release any remaining
> semaphores, the same as is done in the exceptionCaught method of the
> UpstreamHandler. This solves the problem for me.
> Alternatively, we could handle channel close events in handleUpstream(), but
> I'm not sure if Netty automatically reconnects if the server re-appears, in
> which case this wouldn't be a good idea. OTOH, if the server would never come
> back, client threads could hang forever?
> Patch in attachment, against svn r1064125.
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