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From "Colin Patrick McCabe (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-8429) Death of watcherThread making other local read blocked
Date Wed, 20 May 2015 19:06:00 GMT

    [ https://issues.apache.org/jira/browse/HDFS-8429?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14552875#comment-14552875

Colin Patrick McCabe commented on HDFS-8429:

Thanks.  We shouldn't need to modify {{DomainSocketWatcher#add}} and {{DomainSocketWatcher#remove}},
since the finally block clears {{toAdd}} and {{toRemove}} prior to calling {{signalAll}}.
 The modifications to the finally block look reasonable.  I think we are going to need a unit
test for this as well.  Perhaps simply send an interrupt to a thread in the unit test.

> Death of watcherThread making other local read blocked
> ------------------------------------------------------
>                 Key: HDFS-8429
>                 URL: https://issues.apache.org/jira/browse/HDFS-8429
>             Project: Hadoop HDFS
>          Issue Type: Bug
>    Affects Versions: 2.6.0
>            Reporter: zhouyingchao
>            Assignee: zhouyingchao
>         Attachments: HDFS-8429-001.patch
> In our cluster, an application is hung when doing a short circuit read of local hdfs
block. By looking into the log, we found the DataNode's DomainSocketWatcher.watcherThread
has exited with following log:
> {code}
> ERROR org.apache.hadoop.net.unix.DomainSocketWatcher: Thread[Thread-25,5,main] terminating
on unexpected exception
> java.lang.NullPointerException
>         at org.apache.hadoop.net.unix.DomainSocketWatcher$2.run(DomainSocketWatcher.java:463)
>         at java.lang.Thread.run(Thread.java:662)
> {code}
> The line 463 is following code snippet:
> {code}
>          try {
>             for (int fd : fdSet.getAndClearReadableFds()) {
>               sendCallbackAndRemove("getAndClearReadableFds", entries, fdSet,
>                 fd);
>             }
> {code}
> getAndClearReadableFds is a native method which will malloc an int array. Since our memory
is very tight, it looks like the malloc failed and a NULL pointer is returned.
> The bad thing is that other threads then blocked in stack like this:
> {code}
> "DataXceiver for client unix:/home/work/app/hdfs/c3prc-micloud/datanode/dn_socket [Waiting
for operation #1]" daemon prio=10 tid=0x00007f0c9c086d90 nid=0x8fc3 waiting on condition [0x00007f09b9856000]
>    java.lang.Thread.State: WAITING (parking)
>         at sun.misc.Unsafe.park(Native Method)
>         - parking to wait for  <0x00000007b0174808> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
>         at java.util.concurrent.locks.LockSupport.park(LockSupport.java:156)
>         at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1987)
>         at org.apache.hadoop.net.unix.DomainSocketWatcher.add(DomainSocketWatcher.java:323)
>         at org.apache.hadoop.hdfs.server.datanode.ShortCircuitRegistry.createNewMemorySegment(ShortCircuitRegistry.java:322)
>         at org.apache.hadoop.hdfs.server.datanode.DataXceiver.requestShortCircuitShm(DataXceiver.java:403)
>         at org.apache.hadoop.hdfs.protocol.datatransfer.Receiver.opRequestShortCircuitShm(Receiver.java:214)
>         at org.apache.hadoop.hdfs.protocol.datatransfer.Receiver.processOp(Receiver.java:95)
>         at org.apache.hadoop.hdfs.server.datanode.DataXceiver.run(DataXceiver.java:235)
>         at java.lang.Thread.run(Thread.java:662)
> {code}
> IMO, we should exit the DN so that the users can know that something go  wrong  and fix

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