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https://issues.apache.org/jira/browse/HDFS-8429?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14560303#comment-14560303
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zhouyingchao commented on HDFS-8429:
------------------------------------
Colin, thank you for pointing out this issue. I've changed and uploaded the
patch accordingly.
> The DomainSocketWatcher thread should not block other threads if it dies
> ------------------------------------------------------------------------
>
> 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, HDFS-8429-002.patch,
> HDFS-8429-003.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 it.
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