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From whe...@apache.org
Subject [10/12] hadoop git commit: HDFS-8053. Move DFSIn/OutputStream and related classes to hadoop-hdfs-client. Contributed by Mingliang Liu.
Date Sat, 26 Sep 2015 18:17:19 GMT
http://git-wip-us.apache.org/repos/asf/hadoop/blob/94cbb6d1/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSClientFaultInjector.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSClientFaultInjector.java b/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSClientFaultInjector.java
new file mode 100644
index 0000000..12496e2
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSClientFaultInjector.java
@@ -0,0 +1,60 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs;
+
+import java.util.concurrent.atomic.AtomicLong;
+
+import com.google.common.annotations.VisibleForTesting;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+
+/**
+ * Used for injecting faults in DFSClient and DFSOutputStream tests.
+ * Calls into this are a no-op in production code. 
+ */
+@VisibleForTesting
+@InterfaceAudience.Private
+public class DFSClientFaultInjector {
+  private static DFSClientFaultInjector instance = new DFSClientFaultInjector();
+  public static AtomicLong exceptionNum = new AtomicLong(0);
+
+  public static DFSClientFaultInjector get() {
+    return instance;
+  }
+  public static void set(DFSClientFaultInjector instance) {
+    DFSClientFaultInjector.instance = instance;
+  }
+
+  public boolean corruptPacket() {
+    return false;
+  }
+
+  public boolean uncorruptPacket() {
+    return false;
+  }
+
+  public boolean failPacket() {
+    return false;
+  }
+
+  public void startFetchFromDatanode() {}
+
+  public void fetchFromDatanodeException() {}
+
+  public void readFromDatanodeDelay() {}
+}

http://git-wip-us.apache.org/repos/asf/hadoop/blob/94cbb6d1/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSHedgedReadMetrics.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSHedgedReadMetrics.java b/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSHedgedReadMetrics.java
new file mode 100644
index 0000000..2a228e8
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSHedgedReadMetrics.java
@@ -0,0 +1,58 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+
+import java.util.concurrent.atomic.AtomicLong;
+
+/**
+ * The client-side metrics for hedged read feature.
+ * This class has a number of metrics variables that are publicly accessible,
+ * we can grab them from client side, like HBase.
+ */
+@InterfaceAudience.Private
+public class DFSHedgedReadMetrics {
+  public final AtomicLong hedgedReadOps = new AtomicLong();
+  public final AtomicLong hedgedReadOpsWin = new AtomicLong();
+  public final AtomicLong hedgedReadOpsInCurThread = new AtomicLong();
+
+  public void incHedgedReadOps() {
+    hedgedReadOps.incrementAndGet();
+  }
+
+  public void incHedgedReadOpsInCurThread() {
+    hedgedReadOpsInCurThread.incrementAndGet();
+  }
+
+  public void incHedgedReadWins() {
+    hedgedReadOpsWin.incrementAndGet();
+  }
+
+  public long getHedgedReadOps() {
+    return hedgedReadOps.longValue();
+  }
+
+  public long getHedgedReadOpsInCurThread() {
+    return hedgedReadOpsInCurThread.longValue();
+  }
+
+  public long getHedgedReadWins() {
+    return hedgedReadOpsWin.longValue();
+  }
+}

http://git-wip-us.apache.org/repos/asf/hadoop/blob/94cbb6d1/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSInotifyEventInputStream.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSInotifyEventInputStream.java b/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSInotifyEventInputStream.java
new file mode 100644
index 0000000..11a1d29
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSInotifyEventInputStream.java
@@ -0,0 +1,239 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.hdfs;
+
+import com.google.common.collect.Iterators;
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+import org.apache.hadoop.hdfs.inotify.EventBatch;
+import org.apache.hadoop.hdfs.inotify.EventBatchList;
+import org.apache.hadoop.hdfs.inotify.MissingEventsException;
+import org.apache.hadoop.hdfs.protocol.ClientProtocol;
+import org.apache.hadoop.util.Time;
+import org.apache.htrace.Sampler;
+import org.apache.htrace.Trace;
+import org.apache.htrace.TraceScope;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+import java.util.Iterator;
+import java.util.Random;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * Stream for reading inotify events. DFSInotifyEventInputStreams should not
+ * be shared among multiple threads.
+ */
+@InterfaceAudience.Public
+@InterfaceStability.Unstable
+public class DFSInotifyEventInputStream {
+  public static final Logger LOG = LoggerFactory.getLogger(
+      DFSInotifyEventInputStream.class);
+
+  /**
+   * The trace sampler to use when making RPCs to the NameNode.
+   */
+  private final Sampler<?> traceSampler;
+
+  private final ClientProtocol namenode;
+  private Iterator<EventBatch> it;
+  private long lastReadTxid;
+  /**
+   * The most recent txid the NameNode told us it has sync'ed -- helps us
+   * determine how far behind we are in the edit stream.
+   */
+  private long syncTxid;
+  /**
+   * Used to generate wait times in {@link DFSInotifyEventInputStream#take()}.
+   */
+  private Random rng = new Random();
+
+  private static final int INITIAL_WAIT_MS = 10;
+
+  DFSInotifyEventInputStream(Sampler<?> traceSampler, ClientProtocol namenode)
+        throws IOException {
+    // Only consider new transaction IDs.
+    this(traceSampler, namenode, namenode.getCurrentEditLogTxid());
+  }
+
+  DFSInotifyEventInputStream(Sampler traceSampler, ClientProtocol namenode,
+        long lastReadTxid) throws IOException {
+    this.traceSampler = traceSampler;
+    this.namenode = namenode;
+    this.it = Iterators.emptyIterator();
+    this.lastReadTxid = lastReadTxid;
+  }
+
+  /**
+   * Returns the next batch of events in the stream or null if no new
+   * batches are currently available.
+   *
+   * @throws IOException because of network error or edit log
+   * corruption. Also possible if JournalNodes are unresponsive in the
+   * QJM setting (even one unresponsive JournalNode is enough in rare cases),
+   * so catching this exception and retrying at least a few times is
+   * recommended.
+   * @throws MissingEventsException if we cannot return the next batch in the
+   * stream because the data for the events (and possibly some subsequent
+   * events) has been deleted (generally because this stream is a very large
+   * number of transactions behind the current state of the NameNode). It is
+   * safe to continue reading from the stream after this exception is thrown
+   * The next available batch of events will be returned.
+   */
+  public EventBatch poll() throws IOException, MissingEventsException {
+    TraceScope scope =
+        Trace.startSpan("inotifyPoll", traceSampler);
+    try {
+      // need to keep retrying until the NN sends us the latest committed txid
+      if (lastReadTxid == -1) {
+        LOG.debug("poll(): lastReadTxid is -1, reading current txid from NN");
+        lastReadTxid = namenode.getCurrentEditLogTxid();
+        return null;
+      }
+      if (!it.hasNext()) {
+        EventBatchList el = namenode.getEditsFromTxid(lastReadTxid + 1);
+        if (el.getLastTxid() != -1) {
+          // we only want to set syncTxid when we were actually able to read some
+          // edits on the NN -- otherwise it will seem like edits are being
+          // generated faster than we can read them when the problem is really
+          // that we are temporarily unable to read edits
+          syncTxid = el.getSyncTxid();
+          it = el.getBatches().iterator();
+          long formerLastReadTxid = lastReadTxid;
+          lastReadTxid = el.getLastTxid();
+          if (el.getFirstTxid() != formerLastReadTxid + 1) {
+            throw new MissingEventsException(formerLastReadTxid + 1,
+                el.getFirstTxid());
+          }
+        } else {
+          LOG.debug("poll(): read no edits from the NN when requesting edits " +
+            "after txid {}", lastReadTxid);
+          return null;
+        }
+      }
+
+      if (it.hasNext()) { // can be empty if el.getLastTxid != -1 but none of the
+        // newly seen edit log ops actually got converted to events
+        return it.next();
+      } else {
+        return null;
+      }
+    } finally {
+      scope.close();
+    }
+  }
+
+  /**
+   * Return a estimate of how many transaction IDs behind the NameNode's
+   * current state this stream is. Clients should periodically call this method
+   * and check if its result is steadily increasing, which indicates that they
+   * are falling behind (i.e. transaction are being generated faster than the
+   * client is reading them). If a client falls too far behind events may be
+   * deleted before the client can read them.
+   * <p/>
+   * A return value of -1 indicates that an estimate could not be produced, and
+   * should be ignored. The value returned by this method is really only useful
+   * when compared to previous or subsequent returned values.
+   */
+  public long getTxidsBehindEstimate() {
+    if (syncTxid == 0) {
+      return -1;
+    } else {
+      assert syncTxid >= lastReadTxid;
+      // this gives the difference between the last txid we have fetched to the
+      // client and syncTxid at the time we last fetched events from the
+      // NameNode
+      return syncTxid - lastReadTxid;
+    }
+  }
+
+  /**
+   * Returns the next event batch in the stream, waiting up to the specified
+   * amount of time for a new batch. Returns null if one is not available at the
+   * end of the specified amount of time. The time before the method returns may
+   * exceed the specified amount of time by up to the time required for an RPC
+   * to the NameNode.
+   *
+   * @param time number of units of the given TimeUnit to wait
+   * @param tu the desired TimeUnit
+   * @throws IOException see {@link DFSInotifyEventInputStream#poll()}
+   * @throws MissingEventsException
+   * see {@link DFSInotifyEventInputStream#poll()}
+   * @throws InterruptedException if the calling thread is interrupted
+   */
+  public EventBatch poll(long time, TimeUnit tu) throws IOException,
+      InterruptedException, MissingEventsException {
+    TraceScope scope = Trace.startSpan("inotifyPollWithTimeout", traceSampler);
+    EventBatch next = null;
+    try {
+      long initialTime = Time.monotonicNow();
+      long totalWait = TimeUnit.MILLISECONDS.convert(time, tu);
+      long nextWait = INITIAL_WAIT_MS;
+      while ((next = poll()) == null) {
+        long timeLeft = totalWait - (Time.monotonicNow() - initialTime);
+        if (timeLeft <= 0) {
+          LOG.debug("timed poll(): timed out");
+          break;
+        } else if (timeLeft < nextWait * 2) {
+          nextWait = timeLeft;
+        } else {
+          nextWait *= 2;
+        }
+        LOG.debug("timed poll(): poll() returned null, sleeping for {} ms",
+            nextWait);
+        Thread.sleep(nextWait);
+      }
+    } finally {
+      scope.close();
+    }
+    return next;
+  }
+
+  /**
+   * Returns the next batch of events in the stream, waiting indefinitely if
+   * a new batch  is not immediately available.
+   *
+   * @throws IOException see {@link DFSInotifyEventInputStream#poll()}
+   * @throws MissingEventsException see
+   * {@link DFSInotifyEventInputStream#poll()}
+   * @throws InterruptedException if the calling thread is interrupted
+   */
+  public EventBatch take() throws IOException, InterruptedException,
+      MissingEventsException {
+    TraceScope scope = Trace.startSpan("inotifyTake", traceSampler);
+    EventBatch next = null;
+    try {
+      int nextWaitMin = INITIAL_WAIT_MS;
+      while ((next = poll()) == null) {
+        // sleep for a random period between nextWaitMin and nextWaitMin * 2
+        // to avoid stampedes at the NN if there are multiple clients
+        int sleepTime = nextWaitMin + rng.nextInt(nextWaitMin);
+        LOG.debug("take(): poll() returned null, sleeping for {} ms", sleepTime);
+        Thread.sleep(sleepTime);
+        // the maximum sleep is 2 minutes
+        nextWaitMin = Math.min(60000, nextWaitMin * 2);
+      }
+    } finally {
+      scope.close();
+    }
+
+    return next;
+  }
+}

http://git-wip-us.apache.org/repos/asf/hadoop/blob/94cbb6d1/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSInputStream.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSInputStream.java b/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSInputStream.java
new file mode 100644
index 0000000..139a27c
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSInputStream.java
@@ -0,0 +1,1915 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs;
+
+import java.io.EOFException;
+import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.nio.ByteBuffer;
+import java.util.AbstractMap;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.EnumSet;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Set;
+import java.util.concurrent.Callable;
+import java.util.concurrent.CancellationException;
+import java.util.concurrent.CompletionService;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorCompletionService;
+import java.util.concurrent.Future;
+import java.util.concurrent.ThreadLocalRandom;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicBoolean;
+
+import com.google.common.base.Preconditions;
+import org.apache.commons.io.IOUtils;
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.fs.ByteBufferReadable;
+import org.apache.hadoop.fs.ByteBufferUtil;
+import org.apache.hadoop.fs.CanSetDropBehind;
+import org.apache.hadoop.fs.CanSetReadahead;
+import org.apache.hadoop.fs.CanUnbuffer;
+import org.apache.hadoop.fs.ChecksumException;
+import org.apache.hadoop.fs.FSInputStream;
+import org.apache.hadoop.fs.FileEncryptionInfo;
+import org.apache.hadoop.fs.HasEnhancedByteBufferAccess;
+import org.apache.hadoop.fs.ReadOption;
+import org.apache.hadoop.fs.StorageType;
+import org.apache.hadoop.fs.UnresolvedLinkException;
+import org.apache.hadoop.hdfs.client.impl.DfsClientConf;
+import org.apache.hadoop.hdfs.protocol.ClientDatanodeProtocol;
+import org.apache.hadoop.hdfs.protocol.DatanodeInfo;
+import org.apache.hadoop.hdfs.protocol.ExtendedBlock;
+import org.apache.hadoop.hdfs.protocol.LocatedBlock;
+import org.apache.hadoop.hdfs.protocol.LocatedBlocks;
+import org.apache.hadoop.hdfs.protocol.datatransfer.InvalidEncryptionKeyException;
+import org.apache.hadoop.hdfs.security.token.block.BlockTokenIdentifier;
+import org.apache.hadoop.hdfs.security.token.block.InvalidBlockTokenException;
+import org.apache.hadoop.hdfs.server.datanode.CachingStrategy;
+import org.apache.hadoop.hdfs.server.datanode.ReplicaNotFoundException;
+import org.apache.hadoop.hdfs.shortcircuit.ClientMmap;
+import org.apache.hadoop.io.ByteBufferPool;
+import org.apache.hadoop.ipc.RPC;
+import org.apache.hadoop.ipc.RemoteException;
+import org.apache.hadoop.net.NetUtils;
+import org.apache.hadoop.security.token.SecretManager.InvalidToken;
+import org.apache.hadoop.security.token.Token;
+import org.apache.hadoop.util.IdentityHashStore;
+import org.apache.htrace.Span;
+import org.apache.htrace.Trace;
+import org.apache.htrace.TraceScope;
+
+import com.google.common.annotations.VisibleForTesting;
+
+/****************************************************************
+ * DFSInputStream provides bytes from a named file.  It handles 
+ * negotiation of the namenode and various datanodes as necessary.
+ ****************************************************************/
+@InterfaceAudience.Private
+public class DFSInputStream extends FSInputStream
+implements ByteBufferReadable, CanSetDropBehind, CanSetReadahead,
+    HasEnhancedByteBufferAccess, CanUnbuffer {
+  @VisibleForTesting
+  public static boolean tcpReadsDisabledForTesting = false;
+  private long hedgedReadOpsLoopNumForTesting = 0;
+  protected final DFSClient dfsClient;
+  protected AtomicBoolean closed = new AtomicBoolean(false);
+  protected final String src;
+  protected final boolean verifyChecksum;
+
+  // state by stateful read only:
+  // (protected by lock on this)
+  /////
+  private DatanodeInfo currentNode = null;
+  protected LocatedBlock currentLocatedBlock = null;
+  protected long pos = 0;
+  protected long blockEnd = -1;
+  private BlockReader blockReader = null;
+  ////
+
+  // state shared by stateful and positional read:
+  // (protected by lock on infoLock)
+  ////
+  protected LocatedBlocks locatedBlocks = null;
+  private long lastBlockBeingWrittenLength = 0;
+  private FileEncryptionInfo fileEncryptionInfo = null;
+  protected CachingStrategy cachingStrategy;
+  ////
+
+  protected final ReadStatistics readStatistics = new ReadStatistics();
+  // lock for state shared between read and pread
+  // Note: Never acquire a lock on <this> with this lock held to avoid deadlocks
+  //       (it's OK to acquire this lock when the lock on <this> is held)
+  protected final Object infoLock = new Object();
+
+  /**
+   * Track the ByteBuffers that we have handed out to readers.
+   * 
+   * The value type can be either ByteBufferPool or ClientMmap, depending on
+   * whether we this is a memory-mapped buffer or not.
+   */
+  private IdentityHashStore<ByteBuffer, Object> extendedReadBuffers;
+
+  private synchronized IdentityHashStore<ByteBuffer, Object>
+        getExtendedReadBuffers() {
+    if (extendedReadBuffers == null) {
+      extendedReadBuffers = new IdentityHashStore<ByteBuffer, Object>(0);
+    }
+    return extendedReadBuffers;
+  }
+
+  public static class ReadStatistics {
+    public ReadStatistics() {
+      clear();
+    }
+
+    public ReadStatistics(ReadStatistics rhs) {
+      this.totalBytesRead = rhs.getTotalBytesRead();
+      this.totalLocalBytesRead = rhs.getTotalLocalBytesRead();
+      this.totalShortCircuitBytesRead = rhs.getTotalShortCircuitBytesRead();
+      this.totalZeroCopyBytesRead = rhs.getTotalZeroCopyBytesRead();
+    }
+
+    /**
+     * @return The total bytes read.  This will always be at least as
+     * high as the other numbers, since it includes all of them.
+     */
+    public long getTotalBytesRead() {
+      return totalBytesRead;
+    }
+
+    /**
+     * @return The total local bytes read.  This will always be at least
+     * as high as totalShortCircuitBytesRead, since all short-circuit
+     * reads are also local.
+     */
+    public long getTotalLocalBytesRead() {
+      return totalLocalBytesRead;
+    }
+
+    /**
+     * @return The total short-circuit local bytes read.
+     */
+    public long getTotalShortCircuitBytesRead() {
+      return totalShortCircuitBytesRead;
+    }
+    
+    /**
+     * @return The total number of zero-copy bytes read.
+     */
+    public long getTotalZeroCopyBytesRead() {
+      return totalZeroCopyBytesRead;
+    }
+
+    /**
+     * @return The total number of bytes read which were not local.
+     */
+    public long getRemoteBytesRead() {
+      return totalBytesRead - totalLocalBytesRead;
+    }
+    
+    void addRemoteBytes(long amt) {
+      this.totalBytesRead += amt;
+    }
+
+    void addLocalBytes(long amt) {
+      this.totalBytesRead += amt;
+      this.totalLocalBytesRead += amt;
+    }
+
+    void addShortCircuitBytes(long amt) {
+      this.totalBytesRead += amt;
+      this.totalLocalBytesRead += amt;
+      this.totalShortCircuitBytesRead += amt;
+    }
+
+    void addZeroCopyBytes(long amt) {
+      this.totalBytesRead += amt;
+      this.totalLocalBytesRead += amt;
+      this.totalShortCircuitBytesRead += amt;
+      this.totalZeroCopyBytesRead += amt;
+    }
+
+    void clear() {
+      this.totalBytesRead = 0;
+      this.totalLocalBytesRead = 0;
+      this.totalShortCircuitBytesRead = 0;
+      this.totalZeroCopyBytesRead = 0;
+    }
+    
+    private long totalBytesRead;
+
+    private long totalLocalBytesRead;
+
+    private long totalShortCircuitBytesRead;
+
+    private long totalZeroCopyBytesRead;
+  }
+  
+  /**
+   * This variable tracks the number of failures since the start of the
+   * most recent user-facing operation. That is to say, it should be reset
+   * whenever the user makes a call on this stream, and if at any point
+   * during the retry logic, the failure count exceeds a threshold,
+   * the errors will be thrown back to the operation.
+   *
+   * Specifically this counts the number of times the client has gone
+   * back to the namenode to get a new list of block locations, and is
+   * capped at maxBlockAcquireFailures
+   */
+  protected int failures = 0;
+
+  /* XXX Use of CocurrentHashMap is temp fix. Need to fix 
+   * parallel accesses to DFSInputStream (through ptreads) properly */
+  private final ConcurrentHashMap<DatanodeInfo, DatanodeInfo> deadNodes =
+             new ConcurrentHashMap<DatanodeInfo, DatanodeInfo>();
+
+  private byte[] oneByteBuf; // used for 'int read()'
+
+  void addToDeadNodes(DatanodeInfo dnInfo) {
+    deadNodes.put(dnInfo, dnInfo);
+  }
+  
+  DFSInputStream(DFSClient dfsClient, String src, boolean verifyChecksum,
+      LocatedBlocks locatedBlocks) throws IOException, UnresolvedLinkException {
+    this.dfsClient = dfsClient;
+    this.verifyChecksum = verifyChecksum;
+    this.src = src;
+    synchronized (infoLock) {
+      this.cachingStrategy = dfsClient.getDefaultReadCachingStrategy();
+    }
+    this.locatedBlocks = locatedBlocks;
+    openInfo(false);
+  }
+
+  /**
+   * Grab the open-file info from namenode
+   * @param refreshLocatedBlocks whether to re-fetch locatedblocks
+   */
+  void openInfo(boolean refreshLocatedBlocks) throws IOException,
+      UnresolvedLinkException {
+    final DfsClientConf conf = dfsClient.getConf();
+    synchronized(infoLock) {
+      lastBlockBeingWrittenLength =
+          fetchLocatedBlocksAndGetLastBlockLength(refreshLocatedBlocks);
+      int retriesForLastBlockLength = conf.getRetryTimesForGetLastBlockLength();
+      while (retriesForLastBlockLength > 0) {
+        // Getting last block length as -1 is a special case. When cluster
+        // restarts, DNs may not report immediately. At this time partial block
+        // locations will not be available with NN for getting the length. Lets
+        // retry for 3 times to get the length.
+        if (lastBlockBeingWrittenLength == -1) {
+          DFSClient.LOG.warn("Last block locations not available. "
+              + "Datanodes might not have reported blocks completely."
+              + " Will retry for " + retriesForLastBlockLength + " times");
+          waitFor(conf.getRetryIntervalForGetLastBlockLength());
+          lastBlockBeingWrittenLength =
+              fetchLocatedBlocksAndGetLastBlockLength(true);
+        } else {
+          break;
+        }
+        retriesForLastBlockLength--;
+      }
+      if (retriesForLastBlockLength == 0) {
+        throw new IOException("Could not obtain the last block locations.");
+      }
+    }
+  }
+
+  private void waitFor(int waitTime) throws IOException {
+    try {
+      Thread.sleep(waitTime);
+    } catch (InterruptedException e) {
+      throw new IOException(
+          "Interrupted while getting the last block length.");
+    }
+  }
+
+  private long fetchLocatedBlocksAndGetLastBlockLength(boolean refresh)
+      throws IOException {
+    LocatedBlocks newInfo = locatedBlocks;
+    if (locatedBlocks == null || refresh) {
+      newInfo = dfsClient.getLocatedBlocks(src, 0);
+    }
+    if (DFSClient.LOG.isDebugEnabled()) {
+      DFSClient.LOG.debug("newInfo = " + newInfo);
+    }
+    if (newInfo == null) {
+      throw new IOException("Cannot open filename " + src);
+    }
+
+    if (locatedBlocks != null) {
+      Iterator<LocatedBlock> oldIter = locatedBlocks.getLocatedBlocks().iterator();
+      Iterator<LocatedBlock> newIter = newInfo.getLocatedBlocks().iterator();
+      while (oldIter.hasNext() && newIter.hasNext()) {
+        if (! oldIter.next().getBlock().equals(newIter.next().getBlock())) {
+          throw new IOException("Blocklist for " + src + " has changed!");
+        }
+      }
+    }
+    locatedBlocks = newInfo;
+    long lastBlockBeingWrittenLength = 0;
+    if (!locatedBlocks.isLastBlockComplete()) {
+      final LocatedBlock last = locatedBlocks.getLastLocatedBlock();
+      if (last != null) {
+        if (last.getLocations().length == 0) {
+          if (last.getBlockSize() == 0) {
+            // if the length is zero, then no data has been written to
+            // datanode. So no need to wait for the locations.
+            return 0;
+          }
+          return -1;
+        }
+        final long len = readBlockLength(last);
+        last.getBlock().setNumBytes(len);
+        lastBlockBeingWrittenLength = len; 
+      }
+    }
+
+    fileEncryptionInfo = locatedBlocks.getFileEncryptionInfo();
+
+    return lastBlockBeingWrittenLength;
+  }
+
+  /** Read the block length from one of the datanodes. */
+  private long readBlockLength(LocatedBlock locatedblock) throws IOException {
+    assert locatedblock != null : "LocatedBlock cannot be null";
+    int replicaNotFoundCount = locatedblock.getLocations().length;
+    
+    final DfsClientConf conf = dfsClient.getConf();
+    for(DatanodeInfo datanode : locatedblock.getLocations()) {
+      ClientDatanodeProtocol cdp = null;
+      
+      try {
+        cdp = DFSUtilClient.createClientDatanodeProtocolProxy(datanode,
+            dfsClient.getConfiguration(), conf.getSocketTimeout(),
+            conf.isConnectToDnViaHostname(), locatedblock);
+        
+        final long n = cdp.getReplicaVisibleLength(locatedblock.getBlock());
+        
+        if (n >= 0) {
+          return n;
+        }
+      }
+      catch(IOException ioe) {
+        if (ioe instanceof RemoteException &&
+          (((RemoteException) ioe).unwrapRemoteException() instanceof
+            ReplicaNotFoundException)) {
+          // special case : replica might not be on the DN, treat as 0 length
+          replicaNotFoundCount--;
+        }
+        
+        if (DFSClient.LOG.isDebugEnabled()) {
+          DFSClient.LOG.debug("Failed to getReplicaVisibleLength from datanode "
+              + datanode + " for block " + locatedblock.getBlock(), ioe);
+        }
+      } finally {
+        if (cdp != null) {
+          RPC.stopProxy(cdp);
+        }
+      }
+    }
+
+    // Namenode told us about these locations, but none know about the replica
+    // means that we hit the race between pipeline creation start and end.
+    // we require all 3 because some other exception could have happened
+    // on a DN that has it.  we want to report that error
+    if (replicaNotFoundCount == 0) {
+      return 0;
+    }
+
+    throw new IOException("Cannot obtain block length for " + locatedblock);
+  }
+  
+  public long getFileLength() {
+    synchronized(infoLock) {
+      return locatedBlocks == null? 0:
+          locatedBlocks.getFileLength() + lastBlockBeingWrittenLength;
+    }
+  }
+
+  // Short circuit local reads are forbidden for files that are
+  // under construction.  See HDFS-2757.
+  boolean shortCircuitForbidden() {
+    synchronized(infoLock) {
+      return locatedBlocks.isUnderConstruction();
+    }
+  }
+
+  /**
+   * Returns the datanode from which the stream is currently reading.
+   */
+  public synchronized DatanodeInfo getCurrentDatanode() {
+    return currentNode;
+  }
+
+  /**
+   * Returns the block containing the target position. 
+   */
+  synchronized public ExtendedBlock getCurrentBlock() {
+    if (currentLocatedBlock == null){
+      return null;
+    }
+    return currentLocatedBlock.getBlock();
+  }
+
+  /**
+   * Return collection of blocks that has already been located.
+   */
+  public List<LocatedBlock> getAllBlocks() throws IOException {
+    return getBlockRange(0, getFileLength());
+  }
+
+  /**
+   * Get block at the specified position.
+   * Fetch it from the namenode if not cached.
+   * 
+   * @param offset block corresponding to this offset in file is returned
+   * @return located block
+   * @throws IOException
+   */
+  protected LocatedBlock getBlockAt(long offset) throws IOException {
+    synchronized(infoLock) {
+      assert (locatedBlocks != null) : "locatedBlocks is null";
+
+      final LocatedBlock blk;
+
+      //check offset
+      if (offset < 0 || offset >= getFileLength()) {
+        throw new IOException("offset < 0 || offset >= getFileLength(), offset="
+            + offset
+            + ", locatedBlocks=" + locatedBlocks);
+      }
+      else if (offset >= locatedBlocks.getFileLength()) {
+        // offset to the portion of the last block,
+        // which is not known to the name-node yet;
+        // getting the last block
+        blk = locatedBlocks.getLastLocatedBlock();
+      }
+      else {
+        // search cached blocks first
+        int targetBlockIdx = locatedBlocks.findBlock(offset);
+        if (targetBlockIdx < 0) { // block is not cached
+          targetBlockIdx = LocatedBlocks.getInsertIndex(targetBlockIdx);
+          // fetch more blocks
+          final LocatedBlocks newBlocks = dfsClient.getLocatedBlocks(src, offset);
+          assert (newBlocks != null) : "Could not find target position " + offset;
+          locatedBlocks.insertRange(targetBlockIdx, newBlocks.getLocatedBlocks());
+        }
+        blk = locatedBlocks.get(targetBlockIdx);
+      }
+      return blk;
+    }
+  }
+
+  /** Fetch a block from namenode and cache it */
+  protected void fetchBlockAt(long offset) throws IOException {
+    synchronized(infoLock) {
+      int targetBlockIdx = locatedBlocks.findBlock(offset);
+      if (targetBlockIdx < 0) { // block is not cached
+        targetBlockIdx = LocatedBlocks.getInsertIndex(targetBlockIdx);
+      }
+      // fetch blocks
+      final LocatedBlocks newBlocks = dfsClient.getLocatedBlocks(src, offset);
+      if (newBlocks == null) {
+        throw new IOException("Could not find target position " + offset);
+      }
+      locatedBlocks.insertRange(targetBlockIdx, newBlocks.getLocatedBlocks());
+    }
+  }
+
+  /**
+   * Get blocks in the specified range.
+   * Fetch them from the namenode if not cached. This function
+   * will not get a read request beyond the EOF.
+   * @param offset starting offset in file
+   * @param length length of data
+   * @return consequent segment of located blocks
+   * @throws IOException
+   */
+  private List<LocatedBlock> getBlockRange(long offset,
+      long length)  throws IOException {
+    // getFileLength(): returns total file length
+    // locatedBlocks.getFileLength(): returns length of completed blocks
+    if (offset >= getFileLength()) {
+      throw new IOException("Offset: " + offset +
+        " exceeds file length: " + getFileLength());
+    }
+    synchronized(infoLock) {
+      final List<LocatedBlock> blocks;
+      final long lengthOfCompleteBlk = locatedBlocks.getFileLength();
+      final boolean readOffsetWithinCompleteBlk = offset < lengthOfCompleteBlk;
+      final boolean readLengthPastCompleteBlk = offset + length > lengthOfCompleteBlk;
+
+      if (readOffsetWithinCompleteBlk) {
+        //get the blocks of finalized (completed) block range
+        blocks = getFinalizedBlockRange(offset,
+          Math.min(length, lengthOfCompleteBlk - offset));
+      } else {
+        blocks = new ArrayList<LocatedBlock>(1);
+      }
+
+      // get the blocks from incomplete block range
+      if (readLengthPastCompleteBlk) {
+         blocks.add(locatedBlocks.getLastLocatedBlock());
+      }
+
+      return blocks;
+    }
+  }
+
+  /**
+   * Get blocks in the specified range.
+   * Includes only the complete blocks.
+   * Fetch them from the namenode if not cached.
+   */
+  private List<LocatedBlock> getFinalizedBlockRange(
+      long offset, long length) throws IOException {
+    synchronized(infoLock) {
+      assert (locatedBlocks != null) : "locatedBlocks is null";
+      List<LocatedBlock> blockRange = new ArrayList<LocatedBlock>();
+      // search cached blocks first
+      int blockIdx = locatedBlocks.findBlock(offset);
+      if (blockIdx < 0) { // block is not cached
+        blockIdx = LocatedBlocks.getInsertIndex(blockIdx);
+      }
+      long remaining = length;
+      long curOff = offset;
+      while(remaining > 0) {
+        LocatedBlock blk = null;
+        if(blockIdx < locatedBlocks.locatedBlockCount())
+          blk = locatedBlocks.get(blockIdx);
+        if (blk == null || curOff < blk.getStartOffset()) {
+          LocatedBlocks newBlocks;
+          newBlocks = dfsClient.getLocatedBlocks(src, curOff, remaining);
+          locatedBlocks.insertRange(blockIdx, newBlocks.getLocatedBlocks());
+          continue;
+        }
+        assert curOff >= blk.getStartOffset() : "Block not found";
+        blockRange.add(blk);
+        long bytesRead = blk.getStartOffset() + blk.getBlockSize() - curOff;
+        remaining -= bytesRead;
+        curOff += bytesRead;
+        blockIdx++;
+      }
+      return blockRange;
+    }
+  }
+
+  /**
+   * Open a DataInputStream to a DataNode so that it can be read from.
+   * We get block ID and the IDs of the destinations at startup, from the namenode.
+   */
+  private synchronized DatanodeInfo blockSeekTo(long target) throws IOException {
+    if (target >= getFileLength()) {
+      throw new IOException("Attempted to read past end of file");
+    }
+
+    // Will be getting a new BlockReader.
+    closeCurrentBlockReaders();
+
+    //
+    // Connect to best DataNode for desired Block, with potential offset
+    //
+    DatanodeInfo chosenNode = null;
+    int refetchToken = 1; // only need to get a new access token once
+    int refetchEncryptionKey = 1; // only need to get a new encryption key once
+    
+    boolean connectFailedOnce = false;
+
+    while (true) {
+      //
+      // Compute desired block
+      //
+      LocatedBlock targetBlock = getBlockAt(target);
+
+      // update current position
+      this.pos = target;
+      this.blockEnd = targetBlock.getStartOffset() +
+            targetBlock.getBlockSize() - 1;
+      this.currentLocatedBlock = targetBlock;
+
+      long offsetIntoBlock = target - targetBlock.getStartOffset();
+
+      DNAddrPair retval = chooseDataNode(targetBlock, null);
+      chosenNode = retval.info;
+      InetSocketAddress targetAddr = retval.addr;
+      StorageType storageType = retval.storageType;
+
+      try {
+        blockReader = getBlockReader(targetBlock, offsetIntoBlock,
+            targetBlock.getBlockSize() - offsetIntoBlock, targetAddr,
+            storageType, chosenNode);
+        if(connectFailedOnce) {
+          DFSClient.LOG.info("Successfully connected to " + targetAddr +
+                             " for " + targetBlock.getBlock());
+        }
+        return chosenNode;
+      } catch (IOException ex) {
+        if (ex instanceof InvalidEncryptionKeyException && refetchEncryptionKey > 0) {
+          DFSClient.LOG.info("Will fetch a new encryption key and retry, "
+              + "encryption key was invalid when connecting to " + targetAddr
+              + " : " + ex);
+          // The encryption key used is invalid.
+          refetchEncryptionKey--;
+          dfsClient.clearDataEncryptionKey();
+        } else if (refetchToken > 0 && tokenRefetchNeeded(ex, targetAddr)) {
+          refetchToken--;
+          fetchBlockAt(target);
+        } else {
+          connectFailedOnce = true;
+          DFSClient.LOG.warn("Failed to connect to " + targetAddr + " for block"
+            + ", add to deadNodes and continue. " + ex, ex);
+          // Put chosen node into dead list, continue
+          addToDeadNodes(chosenNode);
+        }
+      }
+    }
+  }
+
+  protected BlockReader getBlockReader(LocatedBlock targetBlock,
+      long offsetInBlock, long length, InetSocketAddress targetAddr,
+      StorageType storageType, DatanodeInfo datanode) throws IOException {
+    ExtendedBlock blk = targetBlock.getBlock();
+    Token<BlockTokenIdentifier> accessToken = targetBlock.getBlockToken();
+    CachingStrategy curCachingStrategy;
+    boolean shortCircuitForbidden;
+    synchronized (infoLock) {
+      curCachingStrategy = cachingStrategy;
+      shortCircuitForbidden = shortCircuitForbidden();
+    }
+    return new BlockReaderFactory(dfsClient.getConf()).
+        setInetSocketAddress(targetAddr).
+        setRemotePeerFactory(dfsClient).
+        setDatanodeInfo(datanode).
+        setStorageType(storageType).
+        setFileName(src).
+        setBlock(blk).
+        setBlockToken(accessToken).
+        setStartOffset(offsetInBlock).
+        setVerifyChecksum(verifyChecksum).
+        setClientName(dfsClient.clientName).
+        setLength(length).
+        setCachingStrategy(curCachingStrategy).
+        setAllowShortCircuitLocalReads(!shortCircuitForbidden).
+        setClientCacheContext(dfsClient.getClientContext()).
+        setUserGroupInformation(dfsClient.ugi).
+        setConfiguration(dfsClient.getConfiguration()).
+        build();
+  }
+
+  /**
+   * Close it down!
+   */
+  @Override
+  public synchronized void close() throws IOException {
+    if (!closed.compareAndSet(false, true)) {
+      DFSClient.LOG.debug("DFSInputStream has been closed already");
+      return;
+    }
+    dfsClient.checkOpen();
+
+    if ((extendedReadBuffers != null) && (!extendedReadBuffers.isEmpty())) {
+      final StringBuilder builder = new StringBuilder();
+      extendedReadBuffers.visitAll(new IdentityHashStore.Visitor<ByteBuffer, Object>() {
+        private String prefix = "";
+        @Override
+        public void accept(ByteBuffer k, Object v) {
+          builder.append(prefix).append(k);
+          prefix = ", ";
+        }
+      });
+      DFSClient.LOG.warn("closing file " + src + ", but there are still " +
+          "unreleased ByteBuffers allocated by read().  " +
+          "Please release " + builder.toString() + ".");
+    }
+    closeCurrentBlockReaders();
+    super.close();
+  }
+
+  @Override
+  public synchronized int read() throws IOException {
+    if (oneByteBuf == null) {
+      oneByteBuf = new byte[1];
+    }
+    int ret = read( oneByteBuf, 0, 1 );
+    return ( ret <= 0 ) ? -1 : (oneByteBuf[0] & 0xff);
+  }
+
+  /**
+   * Wraps different possible read implementations so that readBuffer can be
+   * strategy-agnostic.
+   */
+  interface ReaderStrategy {
+    public int doRead(BlockReader blockReader, int off, int len)
+        throws ChecksumException, IOException;
+
+    /**
+     * Copy data from the src ByteBuffer into the read buffer.
+     * @param src The src buffer where the data is copied from
+     * @param offset Useful only when the ReadStrategy is based on a byte array.
+     *               Indicate the offset of the byte array for copy.
+     * @param length Useful only when the ReadStrategy is based on a byte array.
+     *               Indicate the length of the data to copy.
+     */
+    public int copyFrom(ByteBuffer src, int offset, int length);
+  }
+
+  protected void updateReadStatistics(ReadStatistics readStatistics,
+        int nRead, BlockReader blockReader) {
+    if (nRead <= 0) return;
+    synchronized(infoLock) {
+      if (blockReader.isShortCircuit()) {
+        readStatistics.addShortCircuitBytes(nRead);
+      } else if (blockReader.isLocal()) {
+        readStatistics.addLocalBytes(nRead);
+      } else {
+        readStatistics.addRemoteBytes(nRead);
+      }
+    }
+  }
+  
+  /**
+   * Used to read bytes into a byte[]
+   */
+  private class ByteArrayStrategy implements ReaderStrategy {
+    final byte[] buf;
+
+    public ByteArrayStrategy(byte[] buf) {
+      this.buf = buf;
+    }
+
+    @Override
+    public int doRead(BlockReader blockReader, int off, int len)
+          throws ChecksumException, IOException {
+      int nRead = blockReader.read(buf, off, len);
+      updateReadStatistics(readStatistics, nRead, blockReader);
+      return nRead;
+    }
+
+    @Override
+    public int copyFrom(ByteBuffer src, int offset, int length) {
+      ByteBuffer writeSlice = src.duplicate();
+      writeSlice.get(buf, offset, length);
+      return length;
+    }
+  }
+
+  /**
+   * Used to read bytes into a user-supplied ByteBuffer
+   */
+  protected class ByteBufferStrategy implements ReaderStrategy {
+    final ByteBuffer buf;
+    ByteBufferStrategy(ByteBuffer buf) {
+      this.buf = buf;
+    }
+
+    @Override
+    public int doRead(BlockReader blockReader, int off, int len)
+        throws ChecksumException, IOException {
+      int oldpos = buf.position();
+      int oldlimit = buf.limit();
+      boolean success = false;
+      try {
+        int ret = blockReader.read(buf);
+        success = true;
+        updateReadStatistics(readStatistics, ret, blockReader);
+        if (ret == 0) {
+          DFSClient.LOG.warn("zero");
+        }
+        return ret;
+      } finally {
+        if (!success) {
+          // Reset to original state so that retries work correctly.
+          buf.position(oldpos);
+          buf.limit(oldlimit);
+        }
+      } 
+    }
+
+    @Override
+    public int copyFrom(ByteBuffer src, int offset, int length) {
+      ByteBuffer writeSlice = src.duplicate();
+      int remaining = Math.min(buf.remaining(), writeSlice.remaining());
+      writeSlice.limit(writeSlice.position() + remaining);
+      buf.put(writeSlice);
+      return remaining;
+    }
+  }
+
+  /* This is a used by regular read() and handles ChecksumExceptions.
+   * name readBuffer() is chosen to imply similarity to readBuffer() in
+   * ChecksumFileSystem
+   */ 
+  private synchronized int readBuffer(ReaderStrategy reader, int off, int len,
+      Map<ExtendedBlock, Set<DatanodeInfo>> corruptedBlockMap)
+      throws IOException {
+    IOException ioe;
+    
+    /* we retry current node only once. So this is set to true only here.
+     * Intention is to handle one common case of an error that is not a
+     * failure on datanode or client : when DataNode closes the connection
+     * since client is idle. If there are other cases of "non-errors" then
+     * then a datanode might be retried by setting this to true again.
+     */
+    boolean retryCurrentNode = true;
+
+    while (true) {
+      // retry as many times as seekToNewSource allows.
+      try {
+        return reader.doRead(blockReader, off, len);
+      } catch ( ChecksumException ce ) {
+        DFSClient.LOG.warn("Found Checksum error for "
+            + getCurrentBlock() + " from " + currentNode
+            + " at " + ce.getPos());        
+        ioe = ce;
+        retryCurrentNode = false;
+        // we want to remember which block replicas we have tried
+        addIntoCorruptedBlockMap(getCurrentBlock(), currentNode,
+            corruptedBlockMap);
+      } catch ( IOException e ) {
+        if (!retryCurrentNode) {
+          DFSClient.LOG.warn("Exception while reading from "
+              + getCurrentBlock() + " of " + src + " from "
+              + currentNode, e);
+        }
+        ioe = e;
+      }
+      boolean sourceFound = false;
+      if (retryCurrentNode) {
+        /* possibly retry the same node so that transient errors don't
+         * result in application level failures (e.g. Datanode could have
+         * closed the connection because the client is idle for too long).
+         */ 
+        sourceFound = seekToBlockSource(pos);
+      } else {
+        addToDeadNodes(currentNode);
+        sourceFound = seekToNewSource(pos);
+      }
+      if (!sourceFound) {
+        throw ioe;
+      }
+      retryCurrentNode = false;
+    }
+  }
+
+  protected synchronized int readWithStrategy(ReaderStrategy strategy, int off, int len) throws IOException {
+    dfsClient.checkOpen();
+    if (closed.get()) {
+      throw new IOException("Stream closed");
+    }
+    Map<ExtendedBlock,Set<DatanodeInfo>> corruptedBlockMap 
+      = new HashMap<ExtendedBlock, Set<DatanodeInfo>>();
+    failures = 0;
+    if (pos < getFileLength()) {
+      int retries = 2;
+      while (retries > 0) {
+        try {
+          // currentNode can be left as null if previous read had a checksum
+          // error on the same block. See HDFS-3067
+          if (pos > blockEnd || currentNode == null) {
+            currentNode = blockSeekTo(pos);
+          }
+          int realLen = (int) Math.min(len, (blockEnd - pos + 1L));
+          synchronized(infoLock) {
+            if (locatedBlocks.isLastBlockComplete()) {
+              realLen = (int) Math.min(realLen,
+                  locatedBlocks.getFileLength() - pos);
+            }
+          }
+          int result = readBuffer(strategy, off, realLen, corruptedBlockMap);
+          
+          if (result >= 0) {
+            pos += result;
+          } else {
+            // got a EOS from reader though we expect more data on it.
+            throw new IOException("Unexpected EOS from the reader");
+          }
+          if (dfsClient.stats != null) {
+            dfsClient.stats.incrementBytesRead(result);
+          }
+          return result;
+        } catch (ChecksumException ce) {
+          throw ce;            
+        } catch (IOException e) {
+          if (retries == 1) {
+            DFSClient.LOG.warn("DFS Read", e);
+          }
+          blockEnd = -1;
+          if (currentNode != null) { addToDeadNodes(currentNode); }
+          if (--retries == 0) {
+            throw e;
+          }
+        } finally {
+          // Check if need to report block replicas corruption either read
+          // was successful or ChecksumException occured.
+          reportCheckSumFailure(corruptedBlockMap, 
+              currentLocatedBlock.getLocations().length);
+        }
+      }
+    }
+    return -1;
+  }
+
+  /**
+   * Read the entire buffer.
+   */
+  @Override
+  public synchronized int read(final byte buf[], int off, int len) throws IOException {
+    ReaderStrategy byteArrayReader = new ByteArrayStrategy(buf);
+    TraceScope scope =
+        dfsClient.getPathTraceScope("DFSInputStream#byteArrayRead", src);
+    try {
+      return readWithStrategy(byteArrayReader, off, len);
+    } finally {
+      scope.close();
+    }
+  }
+
+  @Override
+  public synchronized int read(final ByteBuffer buf) throws IOException {
+    ReaderStrategy byteBufferReader = new ByteBufferStrategy(buf);
+    TraceScope scope =
+        dfsClient.getPathTraceScope("DFSInputStream#byteBufferRead", src);
+    try {
+      return readWithStrategy(byteBufferReader, 0, buf.remaining());
+    } finally {
+      scope.close();
+    }
+  }
+
+
+  /**
+   * Add corrupted block replica into map.
+   */
+  protected void addIntoCorruptedBlockMap(ExtendedBlock blk, DatanodeInfo node,
+      Map<ExtendedBlock, Set<DatanodeInfo>> corruptedBlockMap) {
+    Set<DatanodeInfo> dnSet = null;
+    if((corruptedBlockMap.containsKey(blk))) {
+      dnSet = corruptedBlockMap.get(blk);
+    }else {
+      dnSet = new HashSet<DatanodeInfo>();
+    }
+    if (!dnSet.contains(node)) {
+      dnSet.add(node);
+      corruptedBlockMap.put(blk, dnSet);
+    }
+  }
+
+  private DNAddrPair chooseDataNode(LocatedBlock block,
+      Collection<DatanodeInfo> ignoredNodes) throws IOException {
+    while (true) {
+      DNAddrPair result = getBestNodeDNAddrPair(block, ignoredNodes);
+      if (result != null) {
+        return result;
+      } else {
+        String errMsg = getBestNodeDNAddrPairErrorString(block.getLocations(),
+          deadNodes, ignoredNodes);
+        String blockInfo = block.getBlock() + " file=" + src;
+        if (failures >= dfsClient.getConf().getMaxBlockAcquireFailures()) {
+          String description = "Could not obtain block: " + blockInfo;
+          DFSClient.LOG.warn(description + errMsg
+              + ". Throwing a BlockMissingException");
+          throw new BlockMissingException(src, description,
+              block.getStartOffset());
+        }
+
+        DatanodeInfo[] nodes = block.getLocations();
+        if (nodes == null || nodes.length == 0) {
+          DFSClient.LOG.info("No node available for " + blockInfo);
+        }
+        DFSClient.LOG.info("Could not obtain " + block.getBlock()
+            + " from any node: " + errMsg
+            + ". Will get new block locations from namenode and retry...");
+        try {
+          // Introducing a random factor to the wait time before another retry.
+          // The wait time is dependent on # of failures and a random factor.
+          // At the first time of getting a BlockMissingException, the wait time
+          // is a random number between 0..3000 ms. If the first retry
+          // still fails, we will wait 3000 ms grace period before the 2nd retry.
+          // Also at the second retry, the waiting window is expanded to 6000 ms
+          // alleviating the request rate from the server. Similarly the 3rd retry
+          // will wait 6000ms grace period before retry and the waiting window is
+          // expanded to 9000ms. 
+          final int timeWindow = dfsClient.getConf().getTimeWindow();
+          double waitTime = timeWindow * failures +       // grace period for the last round of attempt
+              // expanding time window for each failure
+              timeWindow * (failures + 1) *
+              ThreadLocalRandom.current().nextDouble();
+          DFSClient.LOG.warn("DFS chooseDataNode: got # " + (failures + 1) + " IOException, will wait for " + waitTime + " msec.");
+          Thread.sleep((long)waitTime);
+        } catch (InterruptedException iex) {
+        }
+        deadNodes.clear(); //2nd option is to remove only nodes[blockId]
+        openInfo(true);
+        block = refreshLocatedBlock(block);
+        failures++;
+      }
+    }
+  }
+
+  /**
+   * Get the best node from which to stream the data.
+   * @param block LocatedBlock, containing nodes in priority order.
+   * @param ignoredNodes Do not choose nodes in this array (may be null)
+   * @return The DNAddrPair of the best node. Null if no node can be chosen.
+   */
+  protected DNAddrPair getBestNodeDNAddrPair(LocatedBlock block,
+      Collection<DatanodeInfo> ignoredNodes) {
+    DatanodeInfo[] nodes = block.getLocations();
+    StorageType[] storageTypes = block.getStorageTypes();
+    DatanodeInfo chosenNode = null;
+    StorageType storageType = null;
+    if (nodes != null) {
+      for (int i = 0; i < nodes.length; i++) {
+        if (!deadNodes.containsKey(nodes[i])
+            && (ignoredNodes == null || !ignoredNodes.contains(nodes[i]))) {
+          chosenNode = nodes[i];
+          // Storage types are ordered to correspond with nodes, so use the same
+          // index to get storage type.
+          if (storageTypes != null && i < storageTypes.length) {
+            storageType = storageTypes[i];
+          }
+          break;
+        }
+      }
+    }
+    if (chosenNode == null) {
+      DFSClient.LOG.warn("No live nodes contain block " + block.getBlock() +
+          " after checking nodes = " + Arrays.toString(nodes) +
+          ", ignoredNodes = " + ignoredNodes);
+      return null;
+    }
+    final String dnAddr =
+        chosenNode.getXferAddr(dfsClient.getConf().isConnectToDnViaHostname());
+    if (DFSClient.LOG.isDebugEnabled()) {
+      DFSClient.LOG.debug("Connecting to datanode " + dnAddr);
+    }
+    InetSocketAddress targetAddr = NetUtils.createSocketAddr(dnAddr);
+    return new DNAddrPair(chosenNode, targetAddr, storageType);
+  }
+
+  private static String getBestNodeDNAddrPairErrorString(
+      DatanodeInfo nodes[], AbstractMap<DatanodeInfo,
+      DatanodeInfo> deadNodes, Collection<DatanodeInfo> ignoredNodes) {
+    StringBuilder errMsgr = new StringBuilder(
+        " No live nodes contain current block ");
+    errMsgr.append("Block locations:");
+    for (DatanodeInfo datanode : nodes) {
+      errMsgr.append(" ");
+      errMsgr.append(datanode.toString());
+    }
+    errMsgr.append(" Dead nodes: ");
+    for (DatanodeInfo datanode : deadNodes.keySet()) {
+      errMsgr.append(" ");
+      errMsgr.append(datanode.toString());
+    }
+    if (ignoredNodes != null) {
+      errMsgr.append(" Ignored nodes: ");
+      for (DatanodeInfo datanode : ignoredNodes) {
+        errMsgr.append(" ");
+        errMsgr.append(datanode.toString());
+      }
+    }
+    return errMsgr.toString();
+  }
+
+  protected void fetchBlockByteRange(LocatedBlock block, long start, long end,
+      byte[] buf, int offset,
+      Map<ExtendedBlock, Set<DatanodeInfo>> corruptedBlockMap)
+      throws IOException {
+    block = refreshLocatedBlock(block);
+    while (true) {
+      DNAddrPair addressPair = chooseDataNode(block, null);
+      try {
+        actualGetFromOneDataNode(addressPair, block, start, end,
+            buf, offset, corruptedBlockMap);
+        return;
+      } catch (IOException e) {
+        // Ignore. Already processed inside the function.
+        // Loop through to try the next node.
+      }
+    }
+  }
+
+  private Callable<ByteBuffer> getFromOneDataNode(final DNAddrPair datanode,
+      final LocatedBlock block, final long start, final long end,
+      final ByteBuffer bb,
+      final Map<ExtendedBlock, Set<DatanodeInfo>> corruptedBlockMap,
+      final int hedgedReadId) {
+    final Span parentSpan = Trace.currentSpan();
+    return new Callable<ByteBuffer>() {
+      @Override
+      public ByteBuffer call() throws Exception {
+        byte[] buf = bb.array();
+        int offset = bb.position();
+        TraceScope scope =
+            Trace.startSpan("hedgedRead" + hedgedReadId, parentSpan);
+        try {
+          actualGetFromOneDataNode(datanode, block, start, end, buf,
+              offset, corruptedBlockMap);
+          return bb;
+        } finally {
+          scope.close();
+        }
+      }
+    };
+  }
+
+  /**
+   * Used when reading contiguous blocks
+   */
+  private void actualGetFromOneDataNode(final DNAddrPair datanode,
+      LocatedBlock block, final long start, final long end, byte[] buf,
+      int offset, Map<ExtendedBlock, Set<DatanodeInfo>> corruptedBlockMap)
+      throws IOException {
+    final int length = (int) (end - start + 1);
+    actualGetFromOneDataNode(datanode, block, start, end, buf,
+        new int[]{offset}, new int[]{length}, corruptedBlockMap);
+  }
+
+  /**
+   * Read data from one DataNode.
+   * @param datanode the datanode from which to read data
+   * @param block the located block containing the requested data
+   * @param startInBlk the startInBlk offset of the block
+   * @param endInBlk the endInBlk offset of the block
+   * @param buf the given byte array into which the data is read
+   * @param offsets the data may be read into multiple segments of the buf
+   *                (when reading a striped block). this array indicates the
+   *                offset of each buf segment.
+   * @param lengths the length of each buf segment
+   * @param corruptedBlockMap map recording list of datanodes with corrupted
+   *                          block replica
+   */
+  void actualGetFromOneDataNode(final DNAddrPair datanode,
+      LocatedBlock block, final long startInBlk, final long endInBlk,
+      byte[] buf, int[] offsets, int[] lengths,
+      Map<ExtendedBlock, Set<DatanodeInfo>> corruptedBlockMap)
+      throws IOException {
+    DFSClientFaultInjector.get().startFetchFromDatanode();
+    int refetchToken = 1; // only need to get a new access token once
+    int refetchEncryptionKey = 1; // only need to get a new encryption key once
+    final int len = (int) (endInBlk - startInBlk + 1);
+    checkReadPortions(offsets, lengths, len);
+
+    while (true) {
+      // cached block locations may have been updated by chooseDataNode()
+      // or fetchBlockAt(). Always get the latest list of locations at the
+      // start of the loop.
+      block = refreshLocatedBlock(block);
+      BlockReader reader = null;
+      try {
+        DFSClientFaultInjector.get().fetchFromDatanodeException();
+        reader = getBlockReader(block, startInBlk, len, datanode.addr,
+            datanode.storageType, datanode.info);
+        for (int i = 0; i < offsets.length; i++) {
+          int nread = reader.readAll(buf, offsets[i], lengths[i]);
+          updateReadStatistics(readStatistics, nread, reader);
+          if (nread != lengths[i]) {
+            throw new IOException("truncated return from reader.read(): " +
+                "excpected " + lengths[i] + ", got " + nread);
+          }
+        }
+        DFSClientFaultInjector.get().readFromDatanodeDelay();
+        return;
+      } catch (ChecksumException e) {
+        String msg = "fetchBlockByteRange(). Got a checksum exception for "
+            + src + " at " + block.getBlock() + ":" + e.getPos() + " from "
+            + datanode.info;
+        DFSClient.LOG.warn(msg);
+        // we want to remember what we have tried
+        addIntoCorruptedBlockMap(block.getBlock(), datanode.info,
+            corruptedBlockMap);
+        addToDeadNodes(datanode.info);
+        throw new IOException(msg);
+      } catch (IOException e) {
+        if (e instanceof InvalidEncryptionKeyException && refetchEncryptionKey > 0) {
+          DFSClient.LOG.info("Will fetch a new encryption key and retry, " 
+              + "encryption key was invalid when connecting to " + datanode.addr
+              + " : " + e);
+          // The encryption key used is invalid.
+          refetchEncryptionKey--;
+          dfsClient.clearDataEncryptionKey();
+        } else if (refetchToken > 0 && tokenRefetchNeeded(e, datanode.addr)) {
+          refetchToken--;
+          try {
+            fetchBlockAt(block.getStartOffset());
+          } catch (IOException fbae) {
+            // ignore IOE, since we can retry it later in a loop
+          }
+        } else {
+          String msg = "Failed to connect to " + datanode.addr + " for file "
+              + src + " for block " + block.getBlock() + ":" + e;
+          DFSClient.LOG.warn("Connection failure: " + msg, e);
+          addToDeadNodes(datanode.info);
+          throw new IOException(msg);
+        }
+      } finally {
+        if (reader != null) {
+          reader.close();
+        }
+      }
+    }
+  }
+
+  /**
+   * Refresh cached block locations.
+   * @param block The currently cached block locations
+   * @return Refreshed block locations
+   * @throws IOException
+   */
+  protected LocatedBlock refreshLocatedBlock(LocatedBlock block)
+      throws IOException {
+    return getBlockAt(block.getStartOffset());
+  }
+
+  /**
+   * This method verifies that the read portions are valid and do not overlap
+   * with each other.
+   */
+  private void checkReadPortions(int[] offsets, int[] lengths, int totalLen) {
+    Preconditions.checkArgument(offsets.length == lengths.length && offsets.length > 0);
+    int sum = 0;
+    for (int i = 0; i < lengths.length; i++) {
+      if (i > 0) {
+        int gap = offsets[i] - offsets[i - 1];
+        // make sure read portions do not overlap with each other
+        Preconditions.checkArgument(gap >= lengths[i - 1]);
+      }
+      sum += lengths[i];
+    }
+    Preconditions.checkArgument(sum == totalLen);
+  }
+
+  /**
+   * Like {@link #fetchBlockByteRange}except we start up a second, parallel,
+   * 'hedged' read if the first read is taking longer than configured amount of
+   * time. We then wait on which ever read returns first.
+   */
+  private void hedgedFetchBlockByteRange(LocatedBlock block, long start,
+      long end, byte[] buf, int offset,
+      Map<ExtendedBlock, Set<DatanodeInfo>> corruptedBlockMap)
+      throws IOException {
+    final DfsClientConf conf = dfsClient.getConf();
+    ArrayList<Future<ByteBuffer>> futures = new ArrayList<Future<ByteBuffer>>();
+    CompletionService<ByteBuffer> hedgedService =
+        new ExecutorCompletionService<ByteBuffer>(
+        dfsClient.getHedgedReadsThreadPool());
+    ArrayList<DatanodeInfo> ignored = new ArrayList<DatanodeInfo>();
+    ByteBuffer bb = null;
+    int len = (int) (end - start + 1);
+    int hedgedReadId = 0;
+    block = refreshLocatedBlock(block);
+    while (true) {
+      // see HDFS-6591, this metric is used to verify/catch unnecessary loops
+      hedgedReadOpsLoopNumForTesting++;
+      DNAddrPair chosenNode = null;
+      // there is no request already executing.
+      if (futures.isEmpty()) {
+        // chooseDataNode is a commitment. If no node, we go to
+        // the NN to reget block locations. Only go here on first read.
+        chosenNode = chooseDataNode(block, ignored);
+        bb = ByteBuffer.wrap(buf, offset, len);
+        Callable<ByteBuffer> getFromDataNodeCallable = getFromOneDataNode(
+            chosenNode, block, start, end, bb,
+            corruptedBlockMap, hedgedReadId++);
+        Future<ByteBuffer> firstRequest = hedgedService
+            .submit(getFromDataNodeCallable);
+        futures.add(firstRequest);
+        try {
+          Future<ByteBuffer> future = hedgedService.poll(
+              conf.getHedgedReadThresholdMillis(), TimeUnit.MILLISECONDS);
+          if (future != null) {
+            future.get();
+            return;
+          }
+          if (DFSClient.LOG.isDebugEnabled()) {
+            DFSClient.LOG.debug("Waited " + conf.getHedgedReadThresholdMillis()
+                + "ms to read from " + chosenNode.info
+                + "; spawning hedged read");
+          }
+          // Ignore this node on next go around.
+          ignored.add(chosenNode.info);
+          dfsClient.getHedgedReadMetrics().incHedgedReadOps();
+          continue; // no need to refresh block locations
+        } catch (InterruptedException e) {
+          // Ignore
+        } catch (ExecutionException e) {
+          // Ignore already logged in the call.
+        }
+      } else {
+        // We are starting up a 'hedged' read. We have a read already
+        // ongoing. Call getBestNodeDNAddrPair instead of chooseDataNode.
+        // If no nodes to do hedged reads against, pass.
+        try {
+          chosenNode = getBestNodeDNAddrPair(block, ignored);
+          if (chosenNode == null) {
+            chosenNode = chooseDataNode(block, ignored);
+          }
+          bb = ByteBuffer.allocate(len);
+          Callable<ByteBuffer> getFromDataNodeCallable = getFromOneDataNode(
+              chosenNode, block, start, end, bb,
+              corruptedBlockMap, hedgedReadId++);
+          Future<ByteBuffer> oneMoreRequest = hedgedService
+              .submit(getFromDataNodeCallable);
+          futures.add(oneMoreRequest);
+        } catch (IOException ioe) {
+          if (DFSClient.LOG.isDebugEnabled()) {
+            DFSClient.LOG.debug("Failed getting node for hedged read: "
+                + ioe.getMessage());
+          }
+        }
+        // if not succeeded. Submit callables for each datanode in a loop, wait
+        // for a fixed interval and get the result from the fastest one.
+        try {
+          ByteBuffer result = getFirstToComplete(hedgedService, futures);
+          // cancel the rest.
+          cancelAll(futures);
+          if (result.array() != buf) { // compare the array pointers
+            dfsClient.getHedgedReadMetrics().incHedgedReadWins();
+            System.arraycopy(result.array(), result.position(), buf, offset,
+                len);
+          } else {
+            dfsClient.getHedgedReadMetrics().incHedgedReadOps();
+          }
+          return;
+        } catch (InterruptedException ie) {
+          // Ignore and retry
+        }
+        // We got here if exception. Ignore this node on next go around IFF
+        // we found a chosenNode to hedge read against.
+        if (chosenNode != null && chosenNode.info != null) {
+          ignored.add(chosenNode.info);
+        }
+      }
+    }
+  }
+
+  @VisibleForTesting
+  public long getHedgedReadOpsLoopNumForTesting() {
+    return hedgedReadOpsLoopNumForTesting;
+  }
+
+  private ByteBuffer getFirstToComplete(
+      CompletionService<ByteBuffer> hedgedService,
+      ArrayList<Future<ByteBuffer>> futures) throws InterruptedException {
+    if (futures.isEmpty()) {
+      throw new InterruptedException("let's retry");
+    }
+    Future<ByteBuffer> future = null;
+    try {
+      future = hedgedService.take();
+      ByteBuffer bb = future.get();
+      futures.remove(future);
+      return bb;
+    } catch (ExecutionException e) {
+      // already logged in the Callable
+      futures.remove(future);
+    } catch (CancellationException ce) {
+      // already logged in the Callable
+      futures.remove(future);
+    }
+
+    throw new InterruptedException("let's retry");
+  }
+
+  private void cancelAll(List<Future<ByteBuffer>> futures) {
+    for (Future<ByteBuffer> future : futures) {
+      // Unfortunately, hdfs reads do not take kindly to interruption.
+      // Threads return a variety of interrupted-type exceptions but
+      // also complaints about invalid pbs -- likely because read
+      // is interrupted before gets whole pb.  Also verbose WARN
+      // logging.  So, for now, do not interrupt running read.
+      future.cancel(false);
+    }
+  }
+
+  /**
+   * Should the block access token be refetched on an exception
+   * 
+   * @param ex Exception received
+   * @param targetAddr Target datanode address from where exception was received
+   * @return true if block access token has expired or invalid and it should be
+   *         refetched
+   */
+  protected static boolean tokenRefetchNeeded(IOException ex,
+      InetSocketAddress targetAddr) {
+    /*
+     * Get a new access token and retry. Retry is needed in 2 cases. 1)
+     * When both NN and DN re-started while DFSClient holding a cached
+     * access token. 2) In the case that NN fails to update its
+     * access key at pre-set interval (by a wide margin) and
+     * subsequently restarts. In this case, DN re-registers itself with
+     * NN and receives a new access key, but DN will delete the old
+     * access key from its memory since it's considered expired based on
+     * the estimated expiration date.
+     */
+    if (ex instanceof InvalidBlockTokenException || ex instanceof InvalidToken) {
+      DFSClient.LOG.info("Access token was invalid when connecting to "
+          + targetAddr + " : " + ex);
+      return true;
+    }
+    return false;
+  }
+
+  /**
+   * Read bytes starting from the specified position.
+   * 
+   * @param position start read from this position
+   * @param buffer read buffer
+   * @param offset offset into buffer
+   * @param length number of bytes to read
+   * 
+   * @return actual number of bytes read
+   */
+  @Override
+  public int read(long position, byte[] buffer, int offset, int length)
+      throws IOException {
+    TraceScope scope =
+        dfsClient.getPathTraceScope("DFSInputStream#byteArrayPread", src);
+    try {
+      return pread(position, buffer, offset, length);
+    } finally {
+      scope.close();
+    }
+  }
+
+  private int pread(long position, byte[] buffer, int offset, int length)
+      throws IOException {
+    // sanity checks
+    dfsClient.checkOpen();
+    if (closed.get()) {
+      throw new IOException("Stream closed");
+    }
+    failures = 0;
+    long filelen = getFileLength();
+    if ((position < 0) || (position >= filelen)) {
+      return -1;
+    }
+    int realLen = length;
+    if ((position + length) > filelen) {
+      realLen = (int)(filelen - position);
+    }
+    
+    // determine the block and byte range within the block
+    // corresponding to position and realLen
+    List<LocatedBlock> blockRange = getBlockRange(position, realLen);
+    int remaining = realLen;
+    Map<ExtendedBlock,Set<DatanodeInfo>> corruptedBlockMap 
+      = new HashMap<ExtendedBlock, Set<DatanodeInfo>>();
+    for (LocatedBlock blk : blockRange) {
+      long targetStart = position - blk.getStartOffset();
+      long bytesToRead = Math.min(remaining, blk.getBlockSize() - targetStart);
+      try {
+        if (dfsClient.isHedgedReadsEnabled()) {
+          hedgedFetchBlockByteRange(blk, targetStart,
+              targetStart + bytesToRead - 1, buffer, offset, corruptedBlockMap);
+        } else {
+          fetchBlockByteRange(blk, targetStart, targetStart + bytesToRead - 1,
+              buffer, offset, corruptedBlockMap);
+        }
+      } finally {
+        // Check and report if any block replicas are corrupted.
+        // BlockMissingException may be caught if all block replicas are
+        // corrupted.
+        reportCheckSumFailure(corruptedBlockMap, blk.getLocations().length);
+      }
+
+      remaining -= bytesToRead;
+      position += bytesToRead;
+      offset += bytesToRead;
+    }
+    assert remaining == 0 : "Wrong number of bytes read.";
+    if (dfsClient.stats != null) {
+      dfsClient.stats.incrementBytesRead(realLen);
+    }
+    return realLen;
+  }
+  
+  /**
+   * DFSInputStream reports checksum failure.
+   * Case I : client has tried multiple data nodes and at least one of the
+   * attempts has succeeded. We report the other failures as corrupted block to
+   * namenode. 
+   * Case II: client has tried out all data nodes, but all failed. We
+   * only report if the total number of replica is 1. We do not
+   * report otherwise since this maybe due to the client is a handicapped client
+   * (who can not read).
+   * @param corruptedBlockMap map of corrupted blocks
+   * @param dataNodeCount number of data nodes who contains the block replicas
+   */
+  protected void reportCheckSumFailure(
+      Map<ExtendedBlock, Set<DatanodeInfo>> corruptedBlockMap, 
+      int dataNodeCount) {
+    if (corruptedBlockMap.isEmpty()) {
+      return;
+    }
+    Iterator<Entry<ExtendedBlock, Set<DatanodeInfo>>> it = corruptedBlockMap
+        .entrySet().iterator();
+    Entry<ExtendedBlock, Set<DatanodeInfo>> entry = it.next();
+    ExtendedBlock blk = entry.getKey();
+    Set<DatanodeInfo> dnSet = entry.getValue();
+    if (((dnSet.size() < dataNodeCount) && (dnSet.size() > 0))
+        || ((dataNodeCount == 1) && (dnSet.size() == dataNodeCount))) {
+      DatanodeInfo[] locs = new DatanodeInfo[dnSet.size()];
+      int i = 0;
+      for (DatanodeInfo dn:dnSet) {
+        locs[i++] = dn;
+      }
+      LocatedBlock [] lblocks = { new LocatedBlock(blk, locs) };
+      dfsClient.reportChecksumFailure(src, lblocks);
+    }
+    corruptedBlockMap.clear();
+  }
+
+  @Override
+  public long skip(long n) throws IOException {
+    if ( n > 0 ) {
+      long curPos = getPos();
+      long fileLen = getFileLength();
+      if( n+curPos > fileLen ) {
+        n = fileLen - curPos;
+      }
+      seek(curPos+n);
+      return n;
+    }
+    return n < 0 ? -1 : 0;
+  }
+
+  /**
+   * Seek to a new arbitrary location
+   */
+  @Override
+  public synchronized void seek(long targetPos) throws IOException {
+    if (targetPos > getFileLength()) {
+      throw new EOFException("Cannot seek after EOF");
+    }
+    if (targetPos < 0) {
+      throw new EOFException("Cannot seek to negative offset");
+    }
+    if (closed.get()) {
+      throw new IOException("Stream is closed!");
+    }
+    boolean done = false;
+    if (pos <= targetPos && targetPos <= blockEnd) {
+      //
+      // If this seek is to a positive position in the current
+      // block, and this piece of data might already be lying in
+      // the TCP buffer, then just eat up the intervening data.
+      //
+      int diff = (int)(targetPos - pos);
+      if (diff <= blockReader.available()) {
+        try {
+          pos += blockReader.skip(diff);
+          if (pos == targetPos) {
+            done = true;
+          } else {
+            // The range was already checked. If the block reader returns
+            // something unexpected instead of throwing an exception, it is
+            // most likely a bug. 
+            String errMsg = "BlockReader failed to seek to " + 
+                targetPos + ". Instead, it seeked to " + pos + ".";
+            DFSClient.LOG.warn(errMsg);
+            throw new IOException(errMsg);
+          }
+        } catch (IOException e) {//make following read to retry
+          if(DFSClient.LOG.isDebugEnabled()) {
+            DFSClient.LOG.debug("Exception while seek to " + targetPos
+                + " from " + getCurrentBlock() + " of " + src + " from "
+                + currentNode, e);
+          }
+        }
+      }
+    }
+    if (!done) {
+      pos = targetPos;
+      blockEnd = -1;
+    }
+  }
+
+  /**
+   * Same as {@link #seekToNewSource(long)} except that it does not exclude
+   * the current datanode and might connect to the same node.
+   */
+  private boolean seekToBlockSource(long targetPos)
+                                                 throws IOException {
+    currentNode = blockSeekTo(targetPos);
+    return true;
+  }
+  
+  /**
+   * Seek to given position on a node other than the current node.  If
+   * a node other than the current node is found, then returns true. 
+   * If another node could not be found, then returns false.
+   */
+  @Override
+  public synchronized boolean seekToNewSource(long targetPos) throws IOException {
+    if (currentNode == null) {
+      return seekToBlockSource(targetPos);
+    }
+    boolean markedDead = deadNodes.containsKey(currentNode);
+    addToDeadNodes(currentNode);
+    DatanodeInfo oldNode = currentNode;
+    DatanodeInfo newNode = blockSeekTo(targetPos);
+    if (!markedDead) {
+      /* remove it from deadNodes. blockSeekTo could have cleared 
+       * deadNodes and added currentNode again. Thats ok. */
+      deadNodes.remove(oldNode);
+    }
+    if (!oldNode.getDatanodeUuid().equals(newNode.getDatanodeUuid())) {
+      currentNode = newNode;
+      return true;
+    } else {
+      return false;
+    }
+  }
+      
+  /**
+   */
+  @Override
+  public synchronized long getPos() {
+    return pos;
+  }
+
+  /** Return the size of the remaining available bytes
+   * if the size is less than or equal to {@link Integer#MAX_VALUE},
+   * otherwise, return {@link Integer#MAX_VALUE}.
+   */
+  @Override
+  public synchronized int available() throws IOException {
+    if (closed.get()) {
+      throw new IOException("Stream closed");
+    }
+
+    final long remaining = getFileLength() - pos;
+    return remaining <= Integer.MAX_VALUE? (int)remaining: Integer.MAX_VALUE;
+  }
+
+  /**
+   * We definitely don't support marks
+   */
+  @Override
+  public boolean markSupported() {
+    return false;
+  }
+  @Override
+  public void mark(int readLimit) {
+  }
+  @Override
+  public void reset() throws IOException {
+    throw new IOException("Mark/reset not supported");
+  }
+
+  /** Utility class to encapsulate data node info and its address. */
+  static final class DNAddrPair {
+    final DatanodeInfo info;
+    final InetSocketAddress addr;
+    final StorageType storageType;
+
+    DNAddrPair(DatanodeInfo info, InetSocketAddress addr,
+        StorageType storageType) {
+      this.info = info;
+      this.addr = addr;
+      this.storageType = storageType;
+    }
+  }
+
+  /**
+   * Get statistics about the reads which this DFSInputStream has done.
+   */
+  public ReadStatistics getReadStatistics() {
+    synchronized(infoLock) {
+      return new ReadStatistics(readStatistics);
+    }
+  }
+
+  /**
+   * Clear statistics about the reads which this DFSInputStream has done.
+   */
+  public void clearReadStatistics() {
+    synchronized(infoLock) {
+      readStatistics.clear();
+    }
+  }
+
+  public FileEncryptionInfo getFileEncryptionInfo() {
+    synchronized(infoLock) {
+      return fileEncryptionInfo;
+    }
+  }
+
+  protected void closeCurrentBlockReaders() {
+    if (blockReader == null) return;
+    // Close the current block reader so that the new caching settings can 
+    // take effect immediately.
+    try {
+      blockReader.close();
+    } catch (IOException e) {
+      DFSClient.LOG.error("error closing blockReader", e);
+    }
+    blockReader = null;
+    blockEnd = -1;
+  }
+
+  @Override
+  public synchronized void setReadahead(Long readahead)
+      throws IOException {
+    synchronized (infoLock) {
+      this.cachingStrategy =
+          new CachingStrategy.Builder(this.cachingStrategy).setReadahead(readahead).build();
+    }
+    closeCurrentBlockReaders();
+  }
+
+  @Override
+  public synchronized void setDropBehind(Boolean dropBehind)
+      throws IOException {
+    synchronized (infoLock) {
+      this.cachingStrategy =
+          new CachingStrategy.Builder(this.cachingStrategy).setDropBehind(dropBehind).build();
+    }
+    closeCurrentBlockReaders();
+  }
+
+  /**
+   * The immutable empty buffer we return when we reach EOF when doing a
+   * zero-copy read.
+   */
+  private static final ByteBuffer EMPTY_BUFFER =
+    ByteBuffer.allocateDirect(0).asReadOnlyBuffer();
+
+  @Override
+  public synchronized ByteBuffer read(ByteBufferPool bufferPool,
+      int maxLength, EnumSet<ReadOption> opts) 
+          throws IOException, UnsupportedOperationException {
+    if (maxLength == 0) {
+      return EMPTY_BUFFER;
+    } else if (maxLength < 0) {
+      throw new IllegalArgumentException("can't read a negative " +
+          "number of bytes.");
+    }
+    if ((blockReader == null) || (blockEnd == -1)) {
+      if (pos >= getFileLength()) {
+        return null;
+      }
+      /*
+       * If we don't have a blockReader, or the one we have has no more bytes
+       * left to read, we call seekToBlockSource to get a new blockReader and
+       * recalculate blockEnd.  Note that we assume we're not at EOF here
+       * (we check this above).
+       */
+      if ((!seekToBlockSource(pos)) || (blockReader == null)) {
+        throw new IOException("failed to allocate new BlockReader " +
+            "at position " + pos);
+      }
+    }
+    ByteBuffer buffer = null;
+    if (dfsClient.getConf().getShortCircuitConf().isShortCircuitMmapEnabled()) {
+      buffer = tryReadZeroCopy(maxLength, opts);
+    }
+    if (buffer != null) {
+      return buffer;
+    }
+    buffer = ByteBufferUtil.fallbackRead(this, bufferPool, maxLength);
+    if (buffer != null) {
+      getExtendedReadBuffers().put(buffer, bufferPool);
+    }
+    return buffer;
+  }
+
+  private synchronized ByteBuffer tryReadZeroCopy(int maxLength,
+      EnumSet<ReadOption> opts) throws IOException {
+    // Copy 'pos' and 'blockEnd' to local variables to make it easier for the
+    // JVM to optimize this function.
+    final long curPos = pos;
+    final long curEnd = blockEnd;
+    final long blockStartInFile = currentLocatedBlock.getStartOffset();
+    final long blockPos = curPos - blockStartInFile;
+
+    // Shorten this read if the end of the block is nearby.
+    long length63;
+    if ((curPos + maxLength) <= (curEnd + 1)) {
+      length63 = maxLength;
+    } else {
+      length63 = 1 + curEnd - curPos;
+      if (length63 <= 0) {
+        if (DFSClient.LOG.isDebugEnabled()) {
+          DFSClient.LOG.debug("Unable to perform a zero-copy read from offset " +
+            curPos + " of " + src + "; " + length63 + " bytes left in block.  " +
+            "blockPos=" + blockPos + "; curPos=" + curPos +
+            "; curEnd=" + curEnd);
+        }
+        return null;
+      }
+      if (DFSClient.LOG.isDebugEnabled()) {
+        DFSClient.LOG.debug("Reducing read length from " + maxLength +
+            " to " + length63 + " to avoid going more than one byte " +
+            "past the end of the block.  blockPos=" + blockPos +
+            "; curPos=" + curPos + "; curEnd=" + curEnd);
+      }
+    }
+    // Make sure that don't go beyond 31-bit offsets in the MappedByteBuffer.
+    int length;
+    if (blockPos + length63 <= Integer.MAX_VALUE) {
+      length = (int)length63;
+    } else {
+      long length31 = Integer.MAX_VALUE - blockPos;
+      if (length31 <= 0) {
+        // Java ByteBuffers can't be longer than 2 GB, because they use
+        // 4-byte signed integers to represent capacity, etc.
+        // So we can't mmap the parts of the block higher than the 2 GB offset.
+        // FIXME: we could work around this with multiple memory maps.
+        // See HDFS-5101.
+        if (DFSClient.LOG.isDebugEnabled()) {
+          DFSClient.LOG.debug("Unable to perform a zero-copy read from offset " +
+            curPos + " of " + src + "; 31-bit MappedByteBuffer limit " +
+            "exceeded.  blockPos=" + blockPos + ", curEnd=" + curEnd);
+        }
+        return null;
+      }
+      length = (int)length31;
+      if (DFSClient.LOG.isDebugEnabled()) {
+        DFSClient.LOG.debug("Reducing read length from " + maxLength +
+            " to " + length + " to avoid 31-bit limit.  " +
+            "blockPos=" + blockPos + "; curPos=" + curPos +
+            "; curEnd=" + curEnd);
+      }
+    }
+    final ClientMmap clientMmap = blockReader.getClientMmap(opts);
+    if (clientMmap == null) {
+      if (DFSClient.LOG.isDebugEnabled()) {
+        DFSClient.LOG.debug("unable to perform a zero-copy read from offset " +
+          curPos + " of " + src + "; BlockReader#getClientMmap returned " +
+          "null.");
+      }
+      return null;
+    }
+    boolean success = false;
+    ByteBuffer buffer;
+    try {
+      seek(curPos + length);
+      buffer = clientMmap.getMappedByteBuffer().asReadOnlyBuffer();
+      buffer.position((int)blockPos);
+      buffer.limit((int)(blockPos + length));
+      getExtendedReadBuffers().put(buffer, clientMmap);
+      synchronized (infoLock) {
+        readStatistics.addZeroCopyBytes(length);
+      }
+      if (DFSClient.LOG.isDebugEnabled()) {
+        DFSClient.LOG.debug("readZeroCopy read " + length + 
+            " bytes from offset " + curPos + " via the zero-copy read " +
+            "path.  blockEnd = " + blockEnd);
+      }
+      success = true;
+    } finally {
+      if (!success) {
+        IOUtils.closeQuietly(clientMmap);
+      }
+    }
+    return buffer;
+  }
+
+  @Override
+  public synchronized void releaseBuffer(ByteBuffer buffer) {
+    if (buffer == EMPTY_BUFFER) return;
+    Object val = getExtendedReadBuffers().remove(buffer);
+    if (val == null) {
+      throw new IllegalArgumentException("tried to release a buffer " +
+          "that was not created by this stream, " + buffer);
+    }
+    if (val instanceof ClientMmap) {
+      IOUtils.closeQuietly((ClientMmap)val);
+    } else if (val instanceof ByteBufferPool) {
+      ((ByteBufferPool)val).putBuffer(buffer);
+    }
+  }
+
+  @Override
+  public synchronized void unbuffer() {
+    closeCurrentBlockReaders();
+  }
+}


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