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From "Goldstein Lyor (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SSHD-721) deadlock: all nio workers wait to be woken up
Date Sat, 10 Dec 2016 09:23:58 GMT

    [ https://issues.apache.org/jira/browse/SSHD-721?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15737563#comment-15737563
] 

Goldstein Lyor commented on SSHD-721:
-------------------------------------

I don't understand the issue - your [very own remark|https://github.com/maggu2810/sshd-deadlock/tree/first-report]
seems to indicate the problem and its solution:
{quote}
As you can see if the number of workers is not big enough after some time all NIO workers
are waiting and there is no one to wake them up.
{quote}

{{the number of workers is not big enough}} - the SSHD code comes with some reasonable defaults
- if your code needs more resources, then it should configure them (unless I am missing something).
As far as {{All the worker reside in the waitFor function}} - the code seems to be doing what
it was intended. The NIO workers usage depends (indirectly) on the number of concurrent active
sessions. You may have a point about maybe using this pool more optimally - but this is a
separate issue (which you are welcome to open and describe *how* to manage it better - not
a simple task...). Does your code "freeze" when you increase the configured NIO workers thread
pool ? If not, then unless I am missing something, this does not look like a bug but rather
an improvement issue.

> deadlock: all nio workers wait to be woken up
> ---------------------------------------------
>
>                 Key: SSHD-721
>                 URL: https://issues.apache.org/jira/browse/SSHD-721
>             Project: MINA SSHD
>          Issue Type: Bug
>    Affects Versions: 1.3.0, 1.4.0
>            Reporter: Markus Rathgeb
>
> I am using sshd-core for a server machine (S) that accepts incoming connections and port
forwarding requests.
> There are client machines (C) that run servers that should be accessible by a tunnel
to the server.
> On the client machines (C) also an implementation using sshd-core is running that establish
the connection to the server (S) and initiate the port forwarding.
> Other clients are using the tunnelled connection to communicate with the servers that
are running on the client machines (C).
> Sometimes I realized that no data is transferred anymore (through the tunnels).
> All the worker reside in the waitFor function and no one wakes them up.
> {noformat}
> "sshd-SshServer[67de991c]-nio2-thread-3" - Thread t@125
>    java.lang.Thread.State: TIMED_WAITING
> 	at java.lang.Object.wait(Native Method)
> 	- waiting on <132c6b60> (a java.lang.Object)
> 	at org.apache.sshd.client.channel.AbstractClientChannel.waitFor(AbstractClientChannel.java:244)
> 	at org.apache.sshd.common.forward.DefaultTcpipForwarder$StaticIoHandler.messageReceived(DefaultTcpipForwarder.java:984)
> 	at org.apache.sshd.common.io.nio2.Nio2Session.handleReadCycleCompletion(Nio2Session.java:276)
> 	at org.apache.sshd.common.io.nio2.Nio2Session$1.onCompleted(Nio2Session.java:256)
> 	at org.apache.sshd.common.io.nio2.Nio2Session$1.onCompleted(Nio2Session.java:253)
> 	at org.apache.sshd.common.io.nio2.Nio2CompletionHandler.lambda$completed$0(Nio2CompletionHandler.java:38)
> 	at org.apache.sshd.common.io.nio2.Nio2CompletionHandler$$Lambda$45/1071326492.run(Unknown
Source)
> 	at java.security.AccessController.doPrivileged(Native Method)
> 	at org.apache.sshd.common.io.nio2.Nio2CompletionHandler.completed(Nio2CompletionHandler.java:37)
> 	at sun.nio.ch.Invoker.invokeUnchecked(Invoker.java:126)
> 	at sun.nio.ch.Invoker$2.run(Invoker.java:218)
> 	at sun.nio.ch.AsynchronousChannelGroupImpl$1.run(AsynchronousChannelGroupImpl.java:112)
> 	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
> 	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
> 	at java.lang.Thread.run(Thread.java:745)
>    Locked ownable synchronizers:
> 	- locked <6d02d7ed> (a java.util.concurrent.ThreadPoolExecutor$Worker)
> "sshd-SshServer[67de991c]-nio2-thread-2" - Thread t@124
>    java.lang.Thread.State: TIMED_WAITING
> 	at java.lang.Object.wait(Native Method)
> 	- waiting on <7e9f4eff> (a java.lang.Object)
> 	at org.apache.sshd.client.channel.AbstractClientChannel.waitFor(AbstractClientChannel.java:244)
> 	at org.apache.sshd.common.forward.DefaultTcpipForwarder$StaticIoHandler.messageReceived(DefaultTcpipForwarder.java:984)
> 	at org.apache.sshd.common.io.nio2.Nio2Session.handleReadCycleCompletion(Nio2Session.java:276)
> 	at org.apache.sshd.common.io.nio2.Nio2Session$1.onCompleted(Nio2Session.java:256)
> 	at org.apache.sshd.common.io.nio2.Nio2Session$1.onCompleted(Nio2Session.java:253)
> 	at org.apache.sshd.common.io.nio2.Nio2CompletionHandler.lambda$completed$0(Nio2CompletionHandler.java:38)
> 	at org.apache.sshd.common.io.nio2.Nio2CompletionHandler$$Lambda$45/1071326492.run(Unknown
Source)
> 	at java.security.AccessController.doPrivileged(Native Method)
> 	at org.apache.sshd.common.io.nio2.Nio2CompletionHandler.completed(Nio2CompletionHandler.java:37)
> 	at sun.nio.ch.Invoker.invokeUnchecked(Invoker.java:126)
> 	at sun.nio.ch.Invoker$2.run(Invoker.java:218)
> 	at sun.nio.ch.AsynchronousChannelGroupImpl$1.run(AsynchronousChannelGroupImpl.java:112)
> 	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
> 	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
> 	at java.lang.Thread.run(Thread.java:745)
>    Locked ownable synchronizers:
> 	- locked <35fbf3e8> (a java.util.concurrent.ThreadPoolExecutor$Worker)
> "sshd-SshServer[67de991c]-nio2-thread-1" - Thread t@122
>    java.lang.Thread.State: TIMED_WAITING
> 	at java.lang.Object.wait(Native Method)
> 	- waiting on <49ce93a9> (a java.lang.Object)
> 	at org.apache.sshd.client.channel.AbstractClientChannel.waitFor(AbstractClientChannel.java:244)
> 	at org.apache.sshd.common.forward.DefaultTcpipForwarder$StaticIoHandler.messageReceived(DefaultTcpipForwarder.java:984)
> 	at org.apache.sshd.common.io.nio2.Nio2Session.handleReadCycleCompletion(Nio2Session.java:276)
> 	at org.apache.sshd.common.io.nio2.Nio2Session$1.onCompleted(Nio2Session.java:256)
> 	at org.apache.sshd.common.io.nio2.Nio2Session$1.onCompleted(Nio2Session.java:253)
> 	at org.apache.sshd.common.io.nio2.Nio2CompletionHandler.lambda$completed$0(Nio2CompletionHandler.java:38)
> 	at org.apache.sshd.common.io.nio2.Nio2CompletionHandler$$Lambda$45/1071326492.run(Unknown
Source)
> 	at java.security.AccessController.doPrivileged(Native Method)
> 	at org.apache.sshd.common.io.nio2.Nio2CompletionHandler.completed(Nio2CompletionHandler.java:37)
> 	at sun.nio.ch.Invoker.invokeUnchecked(Invoker.java:126)
> 	at sun.nio.ch.Invoker.invokeDirect(Invoker.java:157)
> 	at sun.nio.ch.UnixAsynchronousSocketChannelImpl.implRead(UnixAsynchronousSocketChannelImpl.java:553)
> 	at sun.nio.ch.AsynchronousSocketChannelImpl.read(AsynchronousSocketChannelImpl.java:276)
> 	at sun.nio.ch.AsynchronousSocketChannelImpl.read(AsynchronousSocketChannelImpl.java:297)
> 	at org.apache.sshd.common.io.nio2.Nio2Session.doReadCycle(Nio2Session.java:304)
> 	at org.apache.sshd.common.io.nio2.Nio2Session.doReadCycle(Nio2Session.java:249)
> 	at org.apache.sshd.common.io.nio2.Nio2Session.startReading(Nio2Session.java:243)
> 	at org.apache.sshd.common.io.nio2.Nio2Session.startReading(Nio2Session.java:239)
> 	at org.apache.sshd.common.io.nio2.Nio2Session.startReading(Nio2Session.java:235)
> 	at org.apache.sshd.common.io.nio2.Nio2Session.startReading(Nio2Session.java:231)
> 	at org.apache.sshd.common.io.nio2.Nio2Session.startReading(Nio2Session.java:227)
> 	at org.apache.sshd.common.io.nio2.Nio2Acceptor$AcceptCompletionHandler.onCompleted(Nio2Acceptor.java:178)
> 	at org.apache.sshd.common.io.nio2.Nio2Acceptor$AcceptCompletionHandler.onCompleted(Nio2Acceptor.java:156)
> 	at org.apache.sshd.common.io.nio2.Nio2CompletionHandler.lambda$completed$0(Nio2CompletionHandler.java:38)
> 	at org.apache.sshd.common.io.nio2.Nio2CompletionHandler$$Lambda$45/1071326492.run(Unknown
Source)
> 	at java.security.AccessController.doPrivileged(Native Method)
> 	at org.apache.sshd.common.io.nio2.Nio2CompletionHandler.completed(Nio2CompletionHandler.java:37)
> 	at sun.nio.ch.Invoker.invokeUnchecked(Invoker.java:126)
> 	at sun.nio.ch.Invoker$2.run(Invoker.java:218)
> 	at sun.nio.ch.AsynchronousChannelGroupImpl$1.run(AsynchronousChannelGroupImpl.java:112)
> 	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
> 	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
> 	at java.lang.Thread.run(Thread.java:745)
>    Locked ownable synchronizers:
> 	- locked <7d1c59e6> (a java.util.concurrent.ThreadPoolExecutor$Worker)
> "sshd-SshServer[67de991c]-timer-thread-1" - Thread t@105
>    java.lang.Thread.State: TIMED_WAITING
> 	at sun.misc.Unsafe.park(Native Method)
> 	- parking to wait for <655c080c> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
> 	at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:215)
> 	at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2078)
> 	at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1093)
> 	at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:809)
> 	at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1067)
> 	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1127)
> 	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
> 	at java.lang.Thread.run(Thread.java:745)
>    Locked ownable synchronizers:
> - None
> {noformat}
> To eliminate some other code that could trigger that error I created a "minimal" example
-- a simple test application -- that could be used to demonstrate the hang (for me it is reproducible
using that code).
> Please have a look at https://github.com/maggu2810/sshd-deadlock/tree/first-report where
you could also find a readme with a short description about the code.



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