[SSHD-348] Some SSH threads get blocked in Object.wait() method forever

• Type: Bug
• Status: Resolved
• Priority: Blocker
• Resolution: Fixed
• Affects Version/s: 0.10.0, 0.10.1, 0.11.0, 0.12.0, 0.13.0
• Fix Version/s: 0.14.0
• 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)
• Assignee: Guillaume Nodet
• Reporter: David Ostrovsky
• Created: 12/Sep/14 08:00
• Updated: 19/Dec/19 17:36
• Resolved: 24/Feb/15 15:09

Description

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.

"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)

Issue Links

• depends upon: SSHD-360 Rework CloseableUtils code