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From "Amar Kamat (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4977) Deadlock between reclaimCapacity and assignTasks
Date Mon, 12 Jan 2009 11:39:59 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4977?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12662943#action_12662943

Amar Kamat commented on HADOOP-4977:

Few comments:
- {{updateQSIObjects()}} and {{updateQSIObjects(...)}} might make it confusing as to which
api to use. There seems to be no documentation to clarify which to call when. So I feel we
can have only one api named {{updateQSIObjects()}} which first takes a snapshot of the required
parameters from {{TaskTrackerManager}} and then syncs on the remaining main code.
- there is a extra line which says "for debugging"

> Deadlock between reclaimCapacity and assignTasks
> ------------------------------------------------
>                 Key: HADOOP-4977
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4977
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: contrib/capacity-sched
>    Affects Versions: 0.19.0
>            Reporter: Matei Zaharia
>            Assignee: Vivek Ratan
>            Priority: Blocker
>             Fix For: 0.20.0
>         Attachments: 4977.1.patch, 4977.2.patch, jstack.txt
> I was running the latest trunk with the capacity scheduler and saw the JobTracker lock
up with the following deadlock reported in jstack:
> Found one Java-level deadlock:
> =============================
> "18107298@qtp0-4":
>   waiting to lock monitor 0x08085b40 (object 0x56605100, a org.apache.hadoop.mapred.JobTracker),
>   which is held by "IPC Server handler 4 on 54311"
> "IPC Server handler 4 on 54311":
>   waiting to lock monitor 0x0808594c (object 0x5660e518, a org.apache.hadoop.mapred.CapacityTaskScheduler$MapSchedulingMgr),
>   which is held by "reclaimCapacity"
> "reclaimCapacity":
>   waiting to lock monitor 0x08085b40 (object 0x56605100, a org.apache.hadoop.mapred.JobTracker),
>   which is held by "IPC Server handler 4 on 54311"
> Java stack information for the threads listed above:
> ===================================================
> "18107298@qtp0-4":
> 	at org.apache.hadoop.mapred.JobTracker.getClusterStatus(JobTracker.java:2695)
> 	- waiting to lock <0x56605100> (a org.apache.hadoop.mapred.JobTracker)
> 	at org.apache.hadoop.mapred.jobtracker_jsp._jspService(jobtracker_jsp.java:93)
> 	at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:97)
> 	at javax.servlet.http.HttpServlet.service(HttpServlet.java:820)
> 	at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:502)
> 	at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:363)
> 	at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
> 	at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:181)
> 	at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:766)
> 	at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:417)
> 	at org.mortbay.jetty.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:230)
> 	at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
> 	at org.mortbay.jetty.Server.handle(Server.java:324)
> 	at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:534)
> 	at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:864)
> 	at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:533)
> 	at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:207)
> 	at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:403)
> 	at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:409)
> 	at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:522)
> "IPC Server handler 4 on 54311":
> 	at org.apache.hadoop.mapred.CapacityTaskScheduler$TaskSchedulingMgr.updateQSIObjects(CapacityTaskScheduler.java:564)
> 	- waiting to lock <0x5660e518> (a org.apache.hadoop.mapred.CapacityTaskScheduler$MapSchedulingMgr)
> 	at org.apache.hadoop.mapred.CapacityTaskScheduler$TaskSchedulingMgr.assignTasks(CapacityTaskScheduler.java:855)
> 	at org.apache.hadoop.mapred.CapacityTaskScheduler$TaskSchedulingMgr.access$1000(CapacityTaskScheduler.java:294)
> 	at org.apache.hadoop.mapred.CapacityTaskScheduler.assignTasks(CapacityTaskScheduler.java:1336)
> 	- locked <0x5660dd20> (a org.apache.hadoop.mapred.CapacityTaskScheduler)
> 	at org.apache.hadoop.mapred.JobTracker.heartbeat(JobTracker.java:2288)
> 	- locked <0x56605100> (a org.apache.hadoop.mapred.JobTracker)
> 	at sun.reflect.GeneratedMethodAccessor16.invoke(Unknown Source)
> 	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
> 	at java.lang.reflect.Method.invoke(Method.java:597)
> 	at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:508)
> 	at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:959)
> Unfortunately I didn't manage to select all of the output by mistake, so some is missing,
but it appears that reclaimCapacity locks the MapSchedulingMgr and then tries to lock the
JobTracker, whereas the updateQSIObjects called in assignTasks holds a lock on the JobTracker
(the JobTracker grabs this lock when it calls assignTasks) and then tries to lock the MapSchedulingMgr.
The other thread listed there is a Jetty thread for the web interface and isn't part of the
circular locking. The solution to this would be to lock the JobTracker in reclaimCapacity
before locking anything else.

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