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From "Jitendra Nath Pandey (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-14214) DomainSocketWatcher::add()/delete() should not self interrupt while looping await()
Date Thu, 23 Mar 2017 05:14:41 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-14214?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15937739#comment-15937739
] 

Jitendra Nath Pandey commented on HADOOP-14214:
-----------------------------------------------

The wait is to ensure the domain-socket fd is added to the DomainSocketWatcher thread's collection.
It is a very short wait, but important so that fd's are managed appropriately. The interrupt
is not lost, {{awaitUninterruptibly}} ensures interrupt is set when it returns.

> DomainSocketWatcher::add()/delete() should not self interrupt while looping await()
> -----------------------------------------------------------------------------------
>
>                 Key: HADOOP-14214
>                 URL: https://issues.apache.org/jira/browse/HADOOP-14214
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: hdfs-client
>            Reporter: Mingliang Liu
>            Assignee: Mingliang Liu
>            Priority: Critical
>         Attachments: HADOOP-14214.000.patch
>
>
> Our hive team found a TPCDS job whose queries running on LLAP seem to be getting stuck.
Dozens of threads were waiting for the {{DfsClientShmManager::lock}}, as following jstack:
> {code}
> Thread 251 (IO-Elevator-Thread-5):
>   State: WAITING
>   Blocked count: 3871
>   Wtaited count: 4565
>   Waiting on java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject@16ead198
>   Stack:
>     sun.misc.Unsafe.park(Native Method)
>     java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
>     java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitUninterruptibly(AbstractQueuedSynchronizer.java:1976)
>     org.apache.hadoop.hdfs.shortcircuit.DfsClientShmManager$EndpointShmManager.allocSlot(DfsClientShmManager.java:255)
>     org.apache.hadoop.hdfs.shortcircuit.DfsClientShmManager.allocSlot(DfsClientShmManager.java:434)
>     org.apache.hadoop.hdfs.shortcircuit.ShortCircuitCache.allocShmSlot(ShortCircuitCache.java:1017)
>     org.apache.hadoop.hdfs.BlockReaderFactory.createShortCircuitReplicaInfo(BlockReaderFactory.java:476)
>     org.apache.hadoop.hdfs.shortcircuit.ShortCircuitCache.create(ShortCircuitCache.java:784)
>     org.apache.hadoop.hdfs.shortcircuit.ShortCircuitCache.fetchOrCreate(ShortCircuitCache.java:718)
>     org.apache.hadoop.hdfs.BlockReaderFactory.getBlockReaderLocal(BlockReaderFactory.java:422)
>     org.apache.hadoop.hdfs.BlockReaderFactory.build(BlockReaderFactory.java:333)
>     org.apache.hadoop.hdfs.DFSInputStream.actualGetFromOneDataNode(DFSInputStream.java:1181)
>     org.apache.hadoop.hdfs.DFSInputStream.fetchBlockByteRange(DFSInputStream.java:1118)
>     org.apache.hadoop.hdfs.DFSInputStream.pread(DFSInputStream.java:1478)
>     org.apache.hadoop.hdfs.DFSInputStream.read(DFSInputStream.java:1441)
>     org.apache.hadoop.fs.FSInputStream.readFully(FSInputStream.java:121)
>     org.apache.hadoop.fs.FSDataInputStream.readFully(FSDataInputStream.java:111)
>     org.apache.orc.impl.RecordReaderUtils$DefaultDataReader.readStripeFooter(RecordReaderUtils.java:166)
>     org.apache.hadoop.hive.llap.io.metadata.OrcStripeMetadata.<init>(OrcStripeMetadata.java:64)
>     org.apache.hadoop.hive.llap.io.encoded.OrcEncodedDataReader.readStripesMetadata(OrcEncodedDataReader.java:622)
> {code}
> The thread that is expected to signal those threads is calling {{DomainSocketWatcher::add()}}
method, but it gets stuck there dealing with InterruptedException infinitely. The jstack is
like:
> {code}
> Thread 44417 (TezTR-257387_2840_12_10_52_0):
>   State: RUNNABLE
>   Blocked count: 3
>   Wtaited count: 5
>   Stack:
>     java.lang.Throwable.fillInStackTrace(Native Method)
>     java.lang.Throwable.fillInStackTrace(Throwable.java:783)
>     java.lang.Throwable.<init>(Throwable.java:250)
>     java.lang.Exception.<init>(Exception.java:54)
>     java.lang.InterruptedException.<init>(InterruptedException.java:57)
>     java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2034)
>     org.apache.hadoop.net.unix.DomainSocketWatcher.add(DomainSocketWatcher.java:325)
>     org.apache.hadoop.hdfs.shortcircuit.DfsClientShmManager$EndpointShmManager.allocSlot(DfsClientShmManager.java:266)
>     org.apache.hadoop.hdfs.shortcircuit.DfsClientShmManager.allocSlot(DfsClientShmManager.java:434)
>     org.apache.hadoop.hdfs.shortcircuit.ShortCircuitCache.allocShmSlot(ShortCircuitCache.java:1017)
>     org.apache.hadoop.hdfs.BlockReaderFactory.createShortCircuitReplicaInfo(BlockReaderFactory.java:476)
>     org.apache.hadoop.hdfs.shortcircuit.ShortCircuitCache.create(ShortCircuitCache.java:784)
>     org.apache.hadoop.hdfs.shortcircuit.ShortCircuitCache.fetchOrCreate(ShortCircuitCache.java:718)
>     org.apache.hadoop.hdfs.BlockReaderFactory.getBlockReaderLocal(BlockReaderFactory.java:422)
>     org.apache.hadoop.hdfs.BlockReaderFactory.build(BlockReaderFactory.java:333)
>     org.apache.hadoop.hdfs.DFSInputStream.actualGetFromOneDataNode(DFSInputStream.java:1181)
>     org.apache.hadoop.hdfs.DFSInputStream.fetchBlockByteRange(DFSInputStream.java:1118)
>     org.apache.hadoop.hdfs.DFSInputStream.pread(DFSInputStream.java:1478)
>     org.apache.hadoop.hdfs.DFSInputStream.read(DFSInputStream.java:1441)
>     org.apache.hadoop.fs.FSInputStream.readFully(FSInputStream.java:121)
> {code}
> The whole job makes no progress because of this.
> The thread in {{DomainSocketWatcher::add()}} is expected to eventually break the while
loop where it waits for the newly added entry being deleted by another thread. However, if
this thread is ever interrupted, chances are that it will hold the lock forever so {{if(!toAdd.contains(entry))}}
always be false.
> {code:title=DomainSocketWatcher::add()}
>   public void add(DomainSocket sock, Handler handler) {
>     lock.lock();
>     try {
>       ......
>       toAdd.add(entry);
>       kick();
>       while (true) {
>         try {
>           processedCond.await();
>         } catch (InterruptedException e) {
>           Thread.currentThread().interrupt();
>         }
>         if (!toAdd.contains(entry)) {
>           break;
>         }
>       }
>     } finally {
>       lock.unlock();
>     }
>   }
> {code}
> The reason here is that, this method catches the InterruptedException and self interrupts
during await(). The await() method internally calls {{AbstractQueuedSynchronizer::await()}},
which will throw a new InterruptedException if it's interrupted.
> {code:title=AbstractQueuedSynchronizer::await()}
>         public final void await() throws InterruptedException {
>             if (Thread.interrupted())
>                 throw new InterruptedException();
>             Node node = addConditionWaiter();
>             ...
> {code}
> Our code in {{DomainSocketWatcher::add()}} catches this exception (again) and self interrupt
(again). Please note in this process, the associated lock is never released so that the other
thread which is supposed to make {{if(!toAdd.contains(entry))}} be true is still pending on
the lock.
> {{DomainSocketWatcher::delete()}} has similar code logic and should suffer from similar
problems. 
> Thanks [~jdere] for testing and reporting this.



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