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From Hugo Arès (JIRA) <j...@apache.org>
Subject [jira] [Commented] (SSHD-348) Some SSH threads get blocked in Object.wait() method forever
Date Thu, 11 Dec 2014 16:49:13 GMT

    [ https://issues.apache.org/jira/browse/SSHD-348?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14242768#comment-14242768

Hugo Arès commented on SSHD-348:

More info on the stream-events command and why it's used:
stream-events command is used by anyone who wants to see in events hapenning on the gerrit
server in real time. The connection will not disconnect until the client disconnect and every
time an event is hapenning, client will receive the event detail, one event per line.

The most common use case is for build tools to get notified when something happens on Gerrit
and trigger builds accordingly. The most common integration (a least for our company) is Gerrit-Trigger,
which is a Jenkins plugin. Gerrit-Trigger is using jsch so this is why I only saw stuck threads
with jsch since almost all the stream-events command towards our Gerrit server are initiated
by Gerrit-Trigger.

> Some SSH threads get blocked in Object.wait() method forever
> ------------------------------------------------------------
>                 Key: SSHD-348
>                 URL: https://issues.apache.org/jira/browse/SSHD-348
>             Project: MINA SSHD
>          Issue Type: Bug
>    Affects Versions: 0.10.0, 0.10.1, 0.11.0, 0.12.0, 0.13.0
>         Environment: Gerrit Code Review 2.9.1 (SSHD 0.12.0)
> Gerrit Code Review 2.9.2 (SSHD 0.13.0)
> Gerrit Code Review 2.9.3 (Downgraded to SSHD 0.9)
>            Reporter: David Ostrovsky
>            Assignee: Guillaume Nodet
>            Priority: Blocker
>             Fix For: 0.14.0
>         Attachments: 0001-Prepare-release-sshd-0.13.0-72f868e26.patch, diff
> This seems to be a regression started from 0.10.1.
> In Gerrit we have SSH commamds that returns immediately and so called stream-events command
which keeps connection open until clients disconnect. Basically for days or weeks. This is
used for example to inform CI system (jenkins) about events in gerrit, like new patch set
upload etc.
> In Gerrit we have configurable "SSH-Stream-Worker" thread pool which is dedicated to
the mentioned stream-events SSH command. The observed behaviour on latest SSHD release is
that after some time all threads are stuck. They aren't stuck at the same time, but one after
another untill at some time all threads are stuck and Gerrit must be restarted. Usually after
one week. The stack dump of all such stuck thread are the same, see below. If we had a patch
we could apply it to our production Gerrit instance and try if this helps.
> {code}
> "SSH-Stream-Worker-10" cpu=95400.00 [reset 95400.00] ms elapsed=146444.30 [reset 146444.30]
s allocated=5526700000 B (5.15 GB) [reset 5526700000 B (5.15 GB)] defined_classes=0
> io= file i/o: 15622752/0 B, net i/o: 0/0 B, files opened:0, socks opened:0  [reset file
i/o: 15622752/0 B, net i/o: 0/0 B, files opened:0, socks opened:0 ] 
> prio=10 tid=0x00007f54514df800 nid=0x1c71 / 7281  pthread-id=139999281374976 in Object.wait()
 [_thread_blocked (_at_safepoint), stack(0x00007f541f5f6000,0x00007f541f6f7000)] [0x00007f541f6f5000]
>    java.lang.Thread.State: WAITING (on object monitor)
> 	at java.lang.Object.wait(J)V(Native Method)
> 	- waiting on <0x00007f553aa530d0> (a org.apache.sshd.common.channel.Window)
> 	at java.lang.Object.wait()V(Object.java:503)
> 	at org.apache.sshd.common.channel.Window.waitForSpace()I(Window.java:148)
> 	- locked <0x00007f553aa530d0> (a org.apache.sshd.common.channel.Window)
> 	at org.apache.sshd.common.channel.ChannelOutputStream.flush()V(ChannelOutputStream.java:116)
> 	- locked <0x00007f553aa55060> (a org.apache.sshd.common.channel.ChannelOutputStream)
> 	at org.apache.sshd.common.channel.ChannelOutputStream.write([BII)V(ChannelOutputStream.java:84)
> 	- locked <0x00007f553aa55060> (a org.apache.sshd.common.channel.ChannelOutputStream)
> 	at sun.nio.cs.StreamEncoder.writeBytes()V(StreamEncoder.java:221)
> 	at sun.nio.cs.StreamEncoder.implFlushBuffer()V(StreamEncoder.java:291)
> 	at sun.nio.cs.StreamEncoder.implFlush()V(StreamEncoder.java:295)
> 	at sun.nio.cs.StreamEncoder.flush()V(StreamEncoder.java:141)
> 	- locked <0x00007f553aa7e258> (a java.io.OutputStreamWriter)
> 	at java.io.OutputStreamWriter.flush()V(OutputStreamWriter.java:229)
> 	at java.io.BufferedWriter.flush()V(BufferedWriter.java:254)
> 	- locked <0x00007f553aa7e258> (a java.io.OutputStreamWriter)
> 	at java.io.PrintWriter.flush()V(PrintWriter.java:320)
> 	- locked <0x00007f553aa7e210> (a java.io.BufferedWriter)
> 	at java.io.PrintWriter.checkError()Z(PrintWriter.java:357)
> 	at com.google.gerrit.sshd.commands.StreamEvents.writeEvents()V(StreamEvents.java:186)
> 	at com.google.gerrit.sshd.commands.StreamEvents.access$100(Lcom/google/gerrit/sshd/commands/StreamEvents;)V(StreamEvents.java:43)
> 	at com.google.gerrit.sshd.commands.StreamEvents$3.run()V(StreamEvents.java:82)
> 	at java.util.concurrent.Executors$RunnableAdapter.call()Ljava/lang/Object;(Executors.java:471)
> 	at java.util.concurrent.FutureTask.run()V(FutureTask.java:262)
> 	at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(Ljava/util/concurrent/ScheduledThreadPoolExecutor$ScheduledFutureTask;)V(ScheduledThreadPoolExecutor.java:178)
> 	at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run()V(ScheduledThreadPoolExecutor.java:292)
> 	at com.google.gerrit.server.git.WorkQueue$Task.run()V(WorkQueue.java:364)
> 	at java.util.concurrent.ThreadPoolExecutor.runWorker(Ljava/util/concurrent/ThreadPoolExecutor$Worker;)V(ThreadPoolExecutor.java:1145)
> 	at java.util.concurrent.ThreadPoolExecutor$Worker.run()V(ThreadPoolExecutor.java:615)
> 	at java.lang.Thread.run()V(Thread.java:812)
> {code}

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