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From aengin...@apache.org
Subject [48/50] [abbrv] hadoop git commit: HDFS-9719. Refactoring ErasureCodingWorker into smaller reusable constructs. Contributed by Kai Zheng.
Date Thu, 07 Apr 2016 21:47:16 GMT
HDFS-9719. Refactoring ErasureCodingWorker into smaller reusable constructs. Contributed by Kai Zheng.


Project: http://git-wip-us.apache.org/repos/asf/hadoop/repo
Commit: http://git-wip-us.apache.org/repos/asf/hadoop/commit/3c18a53c
Tree: http://git-wip-us.apache.org/repos/asf/hadoop/tree/3c18a53c
Diff: http://git-wip-us.apache.org/repos/asf/hadoop/diff/3c18a53c

Branch: refs/heads/HDFS-7240
Commit: 3c18a53cbd2efabb2ad108d63a0b0b558424115f
Parents: 8d29e24
Author: Uma Maheswara Rao G <uma.gangumalla@intel.com>
Authored: Wed Apr 6 22:50:24 2016 -0700
Committer: Uma Maheswara Rao G <uma.gangumalla@intel.com>
Committed: Wed Apr 6 22:50:24 2016 -0700

----------------------------------------------------------------------
 .../hadoop/hdfs/util/StripedBlockUtil.java      |   22 +-
 .../erasurecode/ErasureCodingWorker.java        | 1016 +-----------------
 .../erasurecode/StripedBlockReader.java         |  202 ++++
 .../erasurecode/StripedBlockWriter.java         |  196 ++++
 .../datanode/erasurecode/StripedReader.java     |  466 ++++++++
 .../erasurecode/StripedReconstructor.java       |  273 +++++
 .../datanode/erasurecode/StripedWriter.java     |  313 ++++++
 .../datanode/erasurecode/package-info.java      |   26 +
 .../hadoop/hdfs/TestReconstructStripedFile.java |   11 +-
 9 files changed, 1555 insertions(+), 970 deletions(-)
----------------------------------------------------------------------


http://git-wip-us.apache.org/repos/asf/hadoop/blob/3c18a53c/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/util/StripedBlockUtil.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/util/StripedBlockUtil.java b/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/util/StripedBlockUtil.java
index 0819376..c8827d9 100644
--- a/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/util/StripedBlockUtil.java
+++ b/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/util/StripedBlockUtil.java
@@ -141,6 +141,12 @@ public class StripedBlockUtil {
     return locatedBlock;
   }
 
+  public static ExtendedBlock constructInternalBlock(
+      ExtendedBlock blockGroup, ErasureCodingPolicy ecPolicy,
+      int idxInBlockGroup) {
+    return constructInternalBlock(blockGroup, ecPolicy.getCellSize(),
+        ecPolicy.getNumDataUnits(), idxInBlockGroup);
+  }
   /**
    * This method creates an internal {@link ExtendedBlock} at the given index
    * of a block group.
@@ -154,21 +160,28 @@ public class StripedBlockUtil {
     return block;
   }
 
+  public static long getInternalBlockLength(long dataSize,
+                                            ErasureCodingPolicy ecPolicy,
+                                            int idxInBlockGroup) {
+    return getInternalBlockLength(dataSize, ecPolicy.getCellSize(),
+        ecPolicy.getNumDataUnits(), idxInBlockGroup);
+  }
+
   /**
    * Get the size of an internal block at the given index of a block group
    *
    * @param dataSize Size of the block group only counting data blocks
    * @param cellSize The size of a striping cell
    * @param numDataBlocks The number of data blocks
-   * @param i The logical index in the striped block group
+   * @param idxInBlockGroup The logical index in the striped block group
    * @return The size of the internal block at the specified index
    */
   public static long getInternalBlockLength(long dataSize,
-      int cellSize, int numDataBlocks, int i) {
+      int cellSize, int numDataBlocks, int idxInBlockGroup) {
     Preconditions.checkArgument(dataSize >= 0);
     Preconditions.checkArgument(cellSize > 0);
     Preconditions.checkArgument(numDataBlocks > 0);
-    Preconditions.checkArgument(i >= 0);
+    Preconditions.checkArgument(idxInBlockGroup >= 0);
     // Size of each stripe (only counting data blocks)
     final int stripeSize = cellSize * numDataBlocks;
     // If block group ends at stripe boundary, each internal block has an equal
@@ -180,7 +193,8 @@ public class StripedBlockUtil {
 
     final int numStripes = (int) ((dataSize - 1) / stripeSize + 1);
     return (numStripes - 1L)*cellSize
-        + lastCellSize(lastStripeDataLen, cellSize, numDataBlocks, i);
+        + lastCellSize(lastStripeDataLen, cellSize,
+        numDataBlocks, idxInBlockGroup);
   }
 
   /**

http://git-wip-us.apache.org/repos/asf/hadoop/blob/3c18a53c/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/erasurecode/ErasureCodingWorker.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/erasurecode/ErasureCodingWorker.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/erasurecode/ErasureCodingWorker.java
index 4bcb291..e7c5abc 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/erasurecode/ErasureCodingWorker.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/erasurecode/ErasureCodingWorker.java
@@ -17,169 +17,111 @@
  */
 package org.apache.hadoop.hdfs.server.datanode.erasurecode;
 
-import java.io.BufferedOutputStream;
-import java.io.DataInputStream;
-import java.io.DataOutputStream;
-import java.io.IOException;
-import java.io.InputStream;
-import java.io.OutputStream;
-import java.net.InetSocketAddress;
-import java.net.Socket;
-import java.nio.ByteBuffer;
-import java.util.ArrayList;
-import java.util.Arrays;
-import java.util.BitSet;
-import java.util.Collection;
-import java.util.EnumSet;
-import java.util.HashMap;
-import java.util.List;
-import java.util.Map;
-import java.util.concurrent.Callable;
-import java.util.concurrent.CompletionService;
-import java.util.concurrent.ExecutorCompletionService;
-import java.util.concurrent.Future;
-import java.util.concurrent.LinkedBlockingQueue;
-import java.util.concurrent.SynchronousQueue;
-import java.util.concurrent.ThreadPoolExecutor;
-import java.util.concurrent.TimeUnit;
-import java.util.concurrent.atomic.AtomicInteger;
-
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.conf.Configuration;
-import org.apache.hadoop.fs.ChecksumException;
-import org.apache.hadoop.fs.StorageType;
-import org.apache.hadoop.hdfs.BlockReader;
 import org.apache.hadoop.hdfs.DFSConfigKeys;
-import org.apache.hadoop.hdfs.DFSPacket;
-import org.apache.hadoop.hdfs.DFSUtilClient;
-import org.apache.hadoop.hdfs.DFSUtilClient.CorruptedBlocks;
-import org.apache.hadoop.hdfs.RemoteBlockReader2;
-import org.apache.hadoop.hdfs.net.Peer;
-import org.apache.hadoop.hdfs.protocol.DatanodeID;
-import org.apache.hadoop.hdfs.protocol.DatanodeInfo;
-import org.apache.hadoop.hdfs.protocol.ExtendedBlock;
-import org.apache.hadoop.hdfs.protocol.datatransfer.BlockConstructionStage;
-import org.apache.hadoop.hdfs.protocol.datatransfer.IOStreamPair;
-import org.apache.hadoop.hdfs.protocol.datatransfer.PacketHeader;
-import org.apache.hadoop.hdfs.protocol.datatransfer.Sender;
-import org.apache.hadoop.hdfs.protocol.datatransfer.sasl.DataEncryptionKeyFactory;
-import org.apache.hadoop.hdfs.security.token.block.BlockTokenIdentifier;
-import org.apache.hadoop.hdfs.server.datanode.CachingStrategy;
 import org.apache.hadoop.hdfs.server.datanode.DataNode;
 import org.apache.hadoop.hdfs.server.protocol.BlockECReconstructionCommand.BlockECReconstructionInfo;
-import org.apache.hadoop.hdfs.util.StripedBlockUtil;
-import org.apache.hadoop.hdfs.util.StripedBlockUtil.StripingChunkReadResult;
-import org.apache.hadoop.io.IOUtils;
-import org.apache.hadoop.io.erasurecode.CodecUtil;
-import org.apache.hadoop.hdfs.protocol.ErasureCodingPolicy;
-import org.apache.hadoop.io.erasurecode.rawcoder.RawErasureDecoder;
-import org.apache.hadoop.net.NetUtils;
-import org.apache.hadoop.security.token.Token;
 import org.apache.hadoop.util.Daemon;
-import org.apache.hadoop.util.DataChecksum;
-
-import com.google.common.base.Preconditions;
 import org.slf4j.Logger;
 
+import java.util.Collection;
+import java.util.concurrent.LinkedBlockingQueue;
+import java.util.concurrent.SynchronousQueue;
+import java.util.concurrent.ThreadPoolExecutor;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
+
 /**
  * ErasureCodingWorker handles the erasure coding reconstruction work commands.
- * These commands would be issued from Namenode as part of Datanode's heart
- * beat response. BPOfferService delegates the work to this class for handling
- * EC commands.
+ * These commands would be issued from Namenode as part of Datanode's heart beat
+ * response. BPOfferService delegates the work to this class for handling EC
+ * commands.
  */
 @InterfaceAudience.Private
 public final class ErasureCodingWorker {
   private static final Logger LOG = DataNode.LOG;
-  
-  private final DataNode datanode; 
+
+  private final DataNode datanode;
   private final Configuration conf;
 
-  private ThreadPoolExecutor EC_RECONSTRUCTION_STRIPED_BLK_THREAD_POOL;
-  private ThreadPoolExecutor EC_RECONSTRUCTION_STRIPED_READ_THREAD_POOL;
-  private final int EC_RECONSTRUCTION_STRIPED_READ_TIMEOUT_MILLIS;
-  private final int EC_RECONSTRUCTION_STRIPED_READ_BUFFER_SIZE;
+  private ThreadPoolExecutor stripedReconstructionPool;
+  private ThreadPoolExecutor stripedReadPool;
 
   public ErasureCodingWorker(Configuration conf, DataNode datanode) {
     this.datanode = datanode;
     this.conf = conf;
 
-    EC_RECONSTRUCTION_STRIPED_READ_TIMEOUT_MILLIS = conf.getInt(
-        DFSConfigKeys.DFS_DN_EC_RECONSTRUCTION_STRIPED_READ_TIMEOUT_MILLIS_KEY,
-        DFSConfigKeys.DFS_DN_EC_RECONSTRUCTION_STRIPED_READ_TIMEOUT_MILLIS_DEFAULT);
     initializeStripedReadThreadPool(conf.getInt(
         DFSConfigKeys.DFS_DN_EC_RECONSTRUCTION_STRIPED_READ_THREADS_KEY,
         DFSConfigKeys.DFS_DN_EC_RECONSTRUCTION_STRIPED_READ_THREADS_DEFAULT));
-    EC_RECONSTRUCTION_STRIPED_READ_BUFFER_SIZE = conf.getInt(
-        DFSConfigKeys.DFS_DN_EC_RECONSTRUCTION_STRIPED_READ_BUFFER_SIZE_KEY,
-        DFSConfigKeys.DFS_DN_EC_RECONSTRUCTION_STRIPED_READ_BUFFER_SIZE_DEFAULT);
-
     initializeStripedBlkReconstructionThreadPool(conf.getInt(
         DFSConfigKeys.DFS_DN_EC_RECONSTRUCTION_STRIPED_BLK_THREADS_KEY,
         DFSConfigKeys.DFS_DN_EC_RECONSTRUCTION_STRIPED_BLK_THREADS_DEFAULT));
   }
-  
-  private RawErasureDecoder newDecoder(int numDataUnits, int numParityUnits) {
-    return CodecUtil.createRSRawDecoder(conf, numDataUnits, numParityUnits);
-  }
 
   private void initializeStripedReadThreadPool(int num) {
     LOG.debug("Using striped reads; pool threads={}", num);
 
-    EC_RECONSTRUCTION_STRIPED_READ_THREAD_POOL = new ThreadPoolExecutor(1, num,
-        60, TimeUnit.SECONDS, new SynchronousQueue<Runnable>(),
+    stripedReadPool = new ThreadPoolExecutor(1, num, 60, TimeUnit.SECONDS,
+        new SynchronousQueue<Runnable>(),
         new Daemon.DaemonFactory() {
-      private final AtomicInteger threadIndex = new AtomicInteger(0);
+          private final AtomicInteger threadIndex = new AtomicInteger(0);
 
-      @Override
-      public Thread newThread(Runnable r) {
-        Thread t = super.newThread(r);
-        t.setName("stripedRead-" + threadIndex.getAndIncrement());
-        return t;
-      }
-    }, new ThreadPoolExecutor.CallerRunsPolicy() {
-      @Override
-      public void rejectedExecution(Runnable runnable, ThreadPoolExecutor e) {
-        LOG.info("Execution for striped reading rejected, "
-            + "Executing in current thread");
-        // will run in the current thread
-        super.rejectedExecution(runnable, e);
-      }
-    });
-    EC_RECONSTRUCTION_STRIPED_READ_THREAD_POOL.allowCoreThreadTimeOut(true);
+          @Override
+          public Thread newThread(Runnable r) {
+            Thread t = super.newThread(r);
+            t.setName("stripedRead-" + threadIndex.getAndIncrement());
+            return t;
+          }
+        },
+        new ThreadPoolExecutor.CallerRunsPolicy() {
+          @Override
+          public void rejectedExecution(Runnable runnable,
+                                        ThreadPoolExecutor e) {
+            LOG.info("Execution for striped reading rejected, "
+                + "Executing in current thread");
+            // will run in the current thread
+            super.rejectedExecution(runnable, e);
+          }
+        });
+
+    stripedReadPool.allowCoreThreadTimeOut(true);
   }
 
   private void initializeStripedBlkReconstructionThreadPool(int num) {
-    LOG.debug("Using striped block reconstruction; pool threads={}" + num);
-    EC_RECONSTRUCTION_STRIPED_BLK_THREAD_POOL = new ThreadPoolExecutor(2, num,
-        60, TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>(),
+    LOG.debug("Using striped block reconstruction; pool threads={}", num);
+    stripedReconstructionPool = new ThreadPoolExecutor(2, num, 60,
+        TimeUnit.SECONDS,
+        new LinkedBlockingQueue<Runnable>(),
         new Daemon.DaemonFactory() {
           private final AtomicInteger threadIdx = new AtomicInteger(0);
 
           @Override
           public Thread newThread(Runnable r) {
             Thread t = super.newThread(r);
-            t.setName(
-                "stripedBlockReconstruction-" + threadIdx.getAndIncrement());
+            t.setName("stripedBlockReconstruction-"
+                + threadIdx.getAndIncrement());
             return t;
           }
         });
-    EC_RECONSTRUCTION_STRIPED_BLK_THREAD_POOL.allowCoreThreadTimeOut(true);
+    stripedReconstructionPool.allowCoreThreadTimeOut(true);
   }
 
   /**
    * Handles the Erasure Coding reconstruction work commands.
    *
-   * @param ecTasks
-   *          BlockECReconstructionInfo
+   * @param ecTasks BlockECReconstructionInfo
+   *
    */
   public void processErasureCodingTasks(
       Collection<BlockECReconstructionInfo> ecTasks) {
     for (BlockECReconstructionInfo reconstructionInfo : ecTasks) {
       try {
-        ReconstructAndTransferBlock task =
-            new ReconstructAndTransferBlock(reconstructionInfo);
+        final StripedReconstructor task =
+            new StripedReconstructor(this, reconstructionInfo);
         if (task.hasValidTargets()) {
-          EC_RECONSTRUCTION_STRIPED_BLK_THREAD_POOL.submit(task);
+          stripedReconstructionPool.submit(task);
         } else {
           LOG.warn("No missing internal block. Skip reconstruction for task:{}",
               reconstructionInfo);
@@ -191,863 +133,15 @@ public final class ErasureCodingWorker {
     }
   }
 
-  /**
-   * ReconstructAndTransferBlock reconstruct one or more missed striped block
-   * in the striped block group, the minimum number of live striped blocks
-   * should be no less than data block number.
-   * 
-   * | <- Striped Block Group -> |
-   *  blk_0      blk_1       blk_2(*)   blk_3   ...   <- A striped block group
-   *    |          |           |          |  
-   *    v          v           v          v 
-   * +------+   +------+   +------+   +------+
-   * |cell_0|   |cell_1|   |cell_2|   |cell_3|  ...    
-   * +------+   +------+   +------+   +------+     
-   * |cell_4|   |cell_5|   |cell_6|   |cell_7|  ...
-   * +------+   +------+   +------+   +------+
-   * |cell_8|   |cell_9|   |cell10|   |cell11|  ...
-   * +------+   +------+   +------+   +------+
-   *  ...         ...       ...         ...
-   *  
-   * 
-   * We use following steps to reconstruct striped block group, in each round,
-   * we reconstruct <code>bufferSize</code> data until finish, the
-   * <code>bufferSize</code> is configurable and may be less or larger than 
-   * cell size:
-   * step1: read <code>bufferSize</code> data from minimum number of sources 
-   *        required by reconstruction.
-   * step2: decode data for targets.
-   * step3: transfer data to targets.
-   * 
-   * In step1, try to read <code>bufferSize</code> data from minimum number
-   * of sources , if there is corrupt or stale sources, read from new source
-   * will be scheduled. The best sources are remembered for next round and 
-   * may be updated in each round.
-   * 
-   * In step2, typically if source blocks we read are all data blocks, we
-   * need to call encode, and if there is one parity block, we need to call
-   * decode. Notice we only read once and reconstruct all missed striped block
-   * if they are more than one.
-   * 
-   * In step3, send the reconstructed data to targets by constructing packet
-   * and send them directly. Same as continuous block replication, we
-   * don't check the packet ack. Since the datanode doing the reconstruction
-   * work are one of the source datanodes, so the reconstructed data are sent
-   * remotely.
-   * 
-   * There are some points we can do further improvements in next phase:
-   * 1. we can read the block file directly on the local datanode, 
-   *    currently we use remote block reader. (Notice short-circuit is not
-   *    a good choice, see inline comments).
-   * 2. We need to check the packet ack for EC reconstruction? Since EC
-   *    reconstruction is more expensive than continuous block replication,
-   *    it needs to read from several other datanodes, should we make sure
-   *    the reconstructed result received by targets?
-   */
-  private class ReconstructAndTransferBlock implements Runnable {
-    private final int dataBlkNum;
-    private final int parityBlkNum;
-    private final int cellSize;
-    
-    private RawErasureDecoder decoder;
-
-    // Striped read buffer size
-    private int bufferSize;
-
-    private final ExtendedBlock blockGroup;
-    private final int minRequiredSources;
-    // position in striped internal block
-    private long positionInBlock;
-
-    // sources
-    private final byte[] liveIndices;
-    private final DatanodeInfo[] sources;
-
-    private final List<StripedReader> stripedReaders;
-
-    // The buffers and indices for striped blocks whose length is 0
-    private ByteBuffer[] zeroStripeBuffers;
-    private short[] zeroStripeIndices;
-
-    // targets
-    private final DatanodeInfo[] targets;
-    private final StorageType[] targetStorageTypes;
-
-    private final short[] targetIndices;
-    private final ByteBuffer[] targetBuffers;
-
-    private final Socket[] targetSockets;
-    private final DataOutputStream[] targetOutputStreams;
-    private final DataInputStream[] targetInputStreams;
-
-    private final long[] blockOffset4Targets;
-    private final long[] seqNo4Targets;
-
-    private final static int WRITE_PACKET_SIZE = 64 * 1024;
-    private DataChecksum checksum;
-    private int maxChunksPerPacket;
-    private byte[] packetBuf;
-    private byte[] checksumBuf;
-    private int bytesPerChecksum;
-    private int checksumSize;
-
-    private final CachingStrategy cachingStrategy;
-
-    private final Map<Future<Void>, Integer> futures = new HashMap<>();
-    private final CompletionService<Void> readService =
-        new ExecutorCompletionService<>(
-            EC_RECONSTRUCTION_STRIPED_READ_THREAD_POOL);
-    private final boolean hasValidTargets;
-
-    ReconstructAndTransferBlock(BlockECReconstructionInfo reconstructionInfo) {
-      ErasureCodingPolicy ecPolicy = reconstructionInfo
-          .getErasureCodingPolicy();
-      dataBlkNum = ecPolicy.getNumDataUnits();
-      parityBlkNum = ecPolicy.getNumParityUnits();
-      cellSize = ecPolicy.getCellSize();
-
-      blockGroup = reconstructionInfo.getExtendedBlock();
-      final int cellsNum = (int)((blockGroup.getNumBytes() - 1) / cellSize + 1);
-      minRequiredSources = Math.min(cellsNum, dataBlkNum);
-
-      liveIndices = reconstructionInfo.getLiveBlockIndices();
-      sources = reconstructionInfo.getSourceDnInfos();
-      stripedReaders = new ArrayList<>(sources.length);
-
-      Preconditions.checkArgument(liveIndices.length >= minRequiredSources,
-          "No enough live striped blocks.");
-      Preconditions.checkArgument(liveIndices.length == sources.length,
-          "liveBlockIndices and source dns should match");
-
-      if (minRequiredSources < dataBlkNum) {
-        zeroStripeBuffers = 
-            new ByteBuffer[dataBlkNum - minRequiredSources];
-        zeroStripeIndices = new short[dataBlkNum - minRequiredSources];
-      }
-
-      targets = reconstructionInfo.getTargetDnInfos();
-      targetStorageTypes = reconstructionInfo.getTargetStorageTypes();
-      targetIndices = new short[targets.length];
-      targetBuffers = new ByteBuffer[targets.length];
-
-      Preconditions.checkArgument(targetIndices.length <= parityBlkNum,
-          "Too much missed striped blocks.");
-
-      targetSockets = new Socket[targets.length];
-      targetOutputStreams = new DataOutputStream[targets.length];
-      targetInputStreams = new DataInputStream[targets.length];
-
-      blockOffset4Targets = new long[targets.length];
-      seqNo4Targets = new long[targets.length];
-
-      for (int i = 0; i < targets.length; i++) {
-        blockOffset4Targets[i] = 0;
-        seqNo4Targets[i] = 0;
-      }
-
-      hasValidTargets = getTargetIndices();
-      cachingStrategy = CachingStrategy.newDefaultStrategy();
-    }
-
-    boolean hasValidTargets() {
-      return hasValidTargets;
-    }
-
-    private ByteBuffer allocateBuffer(int length) {
-      return ByteBuffer.allocate(length);
-    }
-
-    private ExtendedBlock getBlock(ExtendedBlock blockGroup, int i) {
-      return StripedBlockUtil.constructInternalBlock(blockGroup, cellSize,
-          dataBlkNum, i);
-    }
-
-    private long getBlockLen(ExtendedBlock blockGroup, int i) { 
-      return StripedBlockUtil.getInternalBlockLength(blockGroup.getNumBytes(),
-          cellSize, dataBlkNum, i);
-    }
-
-    /**
-     * StripedReader is used to read from one source DN, it contains a block
-     * reader, buffer and striped block index.
-     * Only allocate StripedReader once for one source, and the StripedReader
-     * has the same array order with sources. Typically we only need to allocate
-     * minimum number (minRequiredSources) of StripedReader, and allocate
-     * new for new source DN if some existing DN invalid or slow.
-     * If some source DN is corrupt, set the corresponding blockReader to 
-     * null and will never read from it again.
-     *  
-     * @param i the array index of sources
-     * @param offsetInBlock offset for the internal block
-     * @return StripedReader
-     */
-    private StripedReader addStripedReader(int i, long offsetInBlock) {
-      final ExtendedBlock block = getBlock(blockGroup, liveIndices[i]);
-      StripedReader reader = new StripedReader(liveIndices[i], block, sources[i]);
-      stripedReaders.add(reader);
-
-      BlockReader blockReader = newBlockReader(block, offsetInBlock, sources[i]);
-      if (blockReader != null) {
-        initChecksumAndBufferSizeIfNeeded(blockReader);
-        reader.blockReader = blockReader;
-      }
-      reader.buffer = allocateBuffer(bufferSize);
-      return reader;
-    }
-
-    @Override
-    public void run() {
-      datanode.incrementXmitsInProgress();
-      try {
-        // Store the array indices of source DNs we have read successfully.
-        // In each iteration of read, the success list may be updated if
-        // some source DN is corrupted or slow. And use the updated success
-        // list of DNs for next iteration read.
-        int[] success = new int[minRequiredSources];
-
-        int nsuccess = 0;
-        for (int i = 0; 
-            i < sources.length && nsuccess < minRequiredSources; i++) {
-          StripedReader reader = addStripedReader(i, 0);
-          if (reader.blockReader != null) {
-            success[nsuccess++] = i;
-          }
-        }
-
-        if (nsuccess < minRequiredSources) {
-          String error = "Can't find minimum sources required by "
-              + "reconstruction, block id: " + blockGroup.getBlockId();
-          throw new IOException(error);
-        }
-
-        if (zeroStripeBuffers != null) {
-          for (int i = 0; i < zeroStripeBuffers.length; i++) {
-            zeroStripeBuffers[i] = allocateBuffer(bufferSize);
-          }
-        }
-
-        for (int i = 0; i < targets.length; i++) {
-          targetBuffers[i] = allocateBuffer(bufferSize);
-        }
-
-        checksumSize = checksum.getChecksumSize();
-        int chunkSize = bytesPerChecksum + checksumSize;
-        maxChunksPerPacket = Math.max(
-            (WRITE_PACKET_SIZE - PacketHeader.PKT_MAX_HEADER_LEN)/chunkSize, 1);
-        int maxPacketSize = chunkSize * maxChunksPerPacket 
-            + PacketHeader.PKT_MAX_HEADER_LEN;
-
-        packetBuf = new byte[maxPacketSize];
-        checksumBuf = new byte[checksumSize * (bufferSize / bytesPerChecksum)];
-
-        // targetsStatus store whether some target is success, it will record
-        // any failed target once, if some target failed (invalid DN or transfer
-        // failed), will not transfer data to it any more.
-        boolean[] targetsStatus = new boolean[targets.length];
-        if (initTargetStreams(targetsStatus) == 0) {
-          String error = "All targets are failed.";
-          throw new IOException(error);
-        }
-
-        long maxTargetLength = 0;
-        for (short targetIndex : targetIndices) {
-          maxTargetLength = Math.max(maxTargetLength,
-              getBlockLen(blockGroup, targetIndex));
-        }
-        while (positionInBlock < maxTargetLength) {
-          final int toReconstruct = (int) Math.min(
-              bufferSize, maxTargetLength - positionInBlock);
-          // step1: read from minimum source DNs required for reconstruction.
-          // The returned success list is the source DNs we do real read from
-          CorruptedBlocks corruptedBlocks = new CorruptedBlocks();
-          try {
-            success = readMinimumStripedData4Reconstruction(success,
-                toReconstruct, corruptedBlocks);
-          } finally {
-            // report corrupted blocks to NN
-            datanode.reportCorruptedBlocks(corruptedBlocks);
-          }
-
-          // step2: decode to reconstruct targets
-          reconstructTargets(success, targetsStatus, toReconstruct);
-
-          // step3: transfer data
-          if (transferData2Targets(targetsStatus) == 0) {
-            String error = "Transfer failed for all targets.";
-            throw new IOException(error);
-          }
-
-          clearBuffers();
-          positionInBlock += toReconstruct;
-        }
-
-        endTargetBlocks(targetsStatus);
-
-        // Currently we don't check the acks for packets, this is similar as
-        // block replication.
-      } catch (Throwable e) {
-        LOG.warn("Failed to reconstruct striped block: {}", blockGroup, e);
-      } finally {
-        datanode.decrementXmitsInProgress();
-        // close block readers
-        for (StripedReader stripedReader : stripedReaders) {
-          IOUtils.closeStream(stripedReader.blockReader);
-        }
-        for (int i = 0; i < targets.length; i++) {
-          IOUtils.closeStream(targetOutputStreams[i]);
-          IOUtils.closeStream(targetInputStreams[i]);
-          IOUtils.closeStream(targetSockets[i]);
-        }
-      }
-    }
-
-    // init checksum from block reader
-    private void initChecksumAndBufferSizeIfNeeded(BlockReader blockReader) {
-      if (checksum == null) {
-        checksum = blockReader.getDataChecksum();
-        bytesPerChecksum = checksum.getBytesPerChecksum();
-        // The bufferSize is flat to divide bytesPerChecksum
-        int readBufferSize = EC_RECONSTRUCTION_STRIPED_READ_BUFFER_SIZE;
-        bufferSize = readBufferSize < bytesPerChecksum ? bytesPerChecksum :
-          readBufferSize - readBufferSize % bytesPerChecksum;
-      } else {
-        assert blockReader.getDataChecksum().equals(checksum);
-      }
-    }
-
-    /**
-     * @return true if there is valid target for reconstruction
-     */
-    private boolean getTargetIndices() {
-      BitSet bitset = new BitSet(dataBlkNum + parityBlkNum);
-      for (int i = 0; i < sources.length; i++) {
-        bitset.set(liveIndices[i]);
-      }
-      int m = 0;
-      int k = 0;
-      boolean hasValidTarget = false;
-      for (int i = 0; i < dataBlkNum + parityBlkNum; i++) {
-        if (!bitset.get(i)) {
-          if (getBlockLen(blockGroup, i) > 0) {
-            if (m < targets.length) {
-              targetIndices[m++] = (short)i;
-              hasValidTarget = true;
-            }
-          } else {
-            zeroStripeIndices[k++] = (short)i;
-          }
-        }
-      }
-      return hasValidTarget;
-    }
-
-    /** the reading length should not exceed the length for reconstruction. */
-    private int getReadLength(int index, int reconstructLength) {
-      long blockLen = getBlockLen(blockGroup, index);
-      long remaining = blockLen - positionInBlock;
-      return (int) Math.min(remaining, reconstructLength);
-    }
-
-    /**
-     * Read from minimum source DNs required for reconstruction in the iteration.
-     * First try the success list which we think they are the best DNs
-     * If source DN is corrupt or slow, try to read some other source DN, 
-     * and will update the success list. 
-     * 
-     * Remember the updated success list and return it for following 
-     * operations and next iteration read.
-     * 
-     * @param success the initial success list of source DNs we think best
-     * @param reconstructLength the length to reconstruct.
-     * @return updated success list of source DNs we do real read
-     * @throws IOException
-     */
-    private int[] readMinimumStripedData4Reconstruction(final int[] success,
-        int reconstructLength, CorruptedBlocks corruptedBlocks)
-            throws IOException {
-      Preconditions.checkArgument(reconstructLength >= 0 &&
-          reconstructLength <= bufferSize);
-      int nsuccess = 0;
-      int[] newSuccess = new int[minRequiredSources];
-      BitSet used = new BitSet(sources.length);
-      /*
-       * Read from minimum source DNs required, the success list contains
-       * source DNs which we think best.
-       */
-      for (int i = 0; i < minRequiredSources; i++) {
-        StripedReader reader = stripedReaders.get(success[i]);
-        final int toRead = getReadLength(liveIndices[success[i]],
-            reconstructLength);
-        if (toRead > 0) {
-          Callable<Void> readCallable = readFromBlock(reader, reader.buffer,
-              toRead, corruptedBlocks);
-          Future<Void> f = readService.submit(readCallable);
-          futures.put(f, success[i]);
-        } else {
-          // If the read length is 0, we don't need to do real read
-          reader.buffer.position(0);
-          newSuccess[nsuccess++] = success[i];
-        }
-        used.set(success[i]);
-      }
-
-      while (!futures.isEmpty()) {
-        try {
-          StripingChunkReadResult result = StripedBlockUtil
-              .getNextCompletedStripedRead(readService, futures,
-                  EC_RECONSTRUCTION_STRIPED_READ_TIMEOUT_MILLIS);
-          int resultIndex = -1;
-          if (result.state == StripingChunkReadResult.SUCCESSFUL) {
-            resultIndex = result.index;
-          } else if (result.state == StripingChunkReadResult.FAILED) {
-            // If read failed for some source DN, we should not use it anymore 
-            // and schedule read from another source DN.
-            StripedReader failedReader = stripedReaders.get(result.index);
-            IOUtils.closeStream(failedReader.blockReader);
-            failedReader.blockReader = null;
-            resultIndex = scheduleNewRead(used, reconstructLength,
-                corruptedBlocks);
-          } else if (result.state == StripingChunkReadResult.TIMEOUT) {
-            // If timeout, we also schedule a new read.
-            resultIndex = scheduleNewRead(used, reconstructLength,
-                corruptedBlocks);
-          }
-          if (resultIndex >= 0) {
-            newSuccess[nsuccess++] = resultIndex;
-            if (nsuccess >= minRequiredSources) {
-              // cancel remaining reads if we read successfully from minimum
-              // number of source DNs required by reconstruction.
-              cancelReads(futures.keySet());
-              futures.clear();
-              break;
-            }
-          }
-        } catch (InterruptedException e) {
-          LOG.info("Read data interrupted.", e);
-          cancelReads(futures.keySet());
-          futures.clear();
-          break;
-        }
-      }
-
-      if (nsuccess < minRequiredSources) {
-        String error = "Can't read data from minimum number of sources "
-            + "required by reconstruction, block id: " + blockGroup.getBlockId();
-        throw new IOException(error);
-      }
-
-      return newSuccess;
-    }
-    
-    private void paddingBufferToLen(ByteBuffer buffer, int len) {
-      if (len > buffer.limit()) {
-        buffer.limit(len);
-      }
-      int toPadding = len - buffer.position();
-      for (int i = 0; i < toPadding; i++) {
-        buffer.put((byte) 0);
-      }
-    }
-    
-    // Initialize decoder
-    private void initDecoderIfNecessary() {
-      if (decoder == null) {
-        decoder = newDecoder(dataBlkNum, parityBlkNum);
-      }
-    }
-
-    private int[] getErasedIndices(boolean[] targetsStatus) {
-      int[] result = new int[targets.length];
-      int m = 0;
-      for (int i = 0; i < targets.length; i++) {
-        if (targetsStatus[i]) {
-          result[m++] = targetIndices[i];
-        }
-      }
-      return Arrays.copyOf(result, m);
-    }
-
-    private void reconstructTargets(int[] success, boolean[] targetsStatus,
-        int toReconstructLen) {
-      initDecoderIfNecessary();
-      ByteBuffer[] inputs = new ByteBuffer[dataBlkNum + parityBlkNum];
-      for (int i = 0; i < success.length; i++) {
-        StripedReader reader = stripedReaders.get(success[i]);
-        ByteBuffer buffer = reader.buffer;
-        paddingBufferToLen(buffer, toReconstructLen);
-        inputs[reader.index] = (ByteBuffer)buffer.flip();
-      }
-      if (success.length < dataBlkNum) {
-        for (int i = 0; i < zeroStripeBuffers.length; i++) {
-          ByteBuffer buffer = zeroStripeBuffers[i];
-          paddingBufferToLen(buffer, toReconstructLen);
-          int index = zeroStripeIndices[i];
-          inputs[index] = (ByteBuffer)buffer.flip();
-        }
-      }
-      int[] erasedIndices = getErasedIndices(targetsStatus);
-      ByteBuffer[] outputs = new ByteBuffer[erasedIndices.length];
-      int m = 0;
-      for (int i = 0; i < targetBuffers.length; i++) {
-        if (targetsStatus[i]) {
-          targetBuffers[i].limit(toReconstructLen);
-          outputs[m++] = targetBuffers[i];
-        }
-      }
-      decoder.decode(inputs, erasedIndices, outputs);
-
-      for (int i = 0; i < targets.length; i++) {
-        if (targetsStatus[i]) {
-          long blockLen = getBlockLen(blockGroup, targetIndices[i]);
-          long remaining = blockLen - positionInBlock;
-          if (remaining <= 0) {
-            targetBuffers[i].limit(0);
-          } else if (remaining < toReconstructLen) {
-            targetBuffers[i].limit((int)remaining);
-          }
-        }
-      }
-    }
-
-    /**
-     * Schedule a read from some new source DN if some DN is corrupted
-     * or slow, this is called from the read iteration.
-     * Initially we may only have <code>minRequiredSources</code> number of 
-     * StripedReader.
-     * If the position is at the end of target block, don't need to do 
-     * real read, and return the array index of source DN, otherwise -1.
-     * 
-     * @param used the used source DNs in this iteration.
-     * @return the array index of source DN if don't need to do real read.
-     */
-    private int scheduleNewRead(BitSet used, int reconstructLen,
-                                CorruptedBlocks corruptedBlocks) {
-      StripedReader reader = null;
-      // step1: initially we may only have <code>minRequiredSources</code>
-      // number of StripedReader, and there may be some source DNs we never 
-      // read before, so will try to create StripedReader for one new source DN
-      // and try to read from it. If found, go to step 3.
-      int m = stripedReaders.size();
-      int toRead = 0;
-      while (reader == null && m < sources.length) {
-        reader = addStripedReader(m, positionInBlock);
-        toRead = getReadLength(liveIndices[m], reconstructLen);
-        if (toRead > 0) {
-          if (reader.blockReader == null) {
-            reader = null;
-            m++;
-          }
-        } else {
-          used.set(m);
-          return m;
-        }
-      }
-
-      // step2: if there is no new source DN we can use, try to find a source 
-      // DN we ever read from but because some reason, e.g., slow, it
-      // is not in the success DN list at the begin of this iteration, so 
-      // we have not tried it in this iteration. Now we have a chance to 
-      // revisit it again.
-      for (int i = 0; reader == null && i < stripedReaders.size(); i++) {
-        if (!used.get(i)) {
-          StripedReader r = stripedReaders.get(i);
-          toRead = getReadLength(liveIndices[i], reconstructLen);
-          if (toRead > 0) {
-            IOUtils.closeStream(r.blockReader);
-            r.blockReader = newBlockReader(
-                getBlock(blockGroup, liveIndices[i]), positionInBlock,
-                sources[i]);
-            if (r.blockReader != null) {
-              r.buffer.position(0);
-              m = i;
-              reader = r;
-            }
-          } else {
-            used.set(i);
-            r.buffer.position(0);
-            return i;
-          }
-        }
-      }
-
-      // step3: schedule if find a correct source DN and need to do real read.
-      if (reader != null) {
-        Callable<Void> readCallable = readFromBlock(reader, reader.buffer,
-            toRead, corruptedBlocks);
-        Future<Void> f = readService.submit(readCallable);
-        futures.put(f, m);
-        used.set(m);
-      }
-
-      return -1;
-    }
-
-    // cancel all reads.
-    private void cancelReads(Collection<Future<Void>> futures) {
-      for (Future<Void> future : futures) {
-        future.cancel(true);
-      }
-    }
-
-    private Callable<Void> readFromBlock(final StripedReader reader,
-        final ByteBuffer buf, final int length,
-        final CorruptedBlocks corruptedBlocks) {
-      return new Callable<Void>() {
-
-        @Override
-        public Void call() throws Exception {
-          try {
-            buf.limit(length);
-            actualReadFromBlock(reader.blockReader, buf);
-            return null;
-          } catch (ChecksumException e) {
-            LOG.warn("Found Checksum error for {} from {} at {}", reader.block,
-                reader.source, e.getPos());
-            corruptedBlocks.addCorruptedBlock(reader.block, reader.source);
-            throw e;
-          } catch (IOException e) {
-            LOG.info(e.getMessage());
-            throw e;
-          }
-        }
-
-      };
-    }
-
-    /**
-     * Read bytes from block
-     */
-    private void actualReadFromBlock(BlockReader reader, ByteBuffer buf)
-        throws IOException {
-      int len = buf.remaining();
-      int n = 0;
-      while (n < len) {
-        int nread = reader.read(buf);
-        if (nread <= 0) {
-          break;
-        }
-        n += nread;
-      }
-    }
-
-    private InetSocketAddress getSocketAddress4Transfer(DatanodeInfo dnInfo) {
-      return NetUtils.createSocketAddr(dnInfo.getXferAddr(
-          datanode.getDnConf().getConnectToDnViaHostname()));
-    }
-
-    private BlockReader newBlockReader(final ExtendedBlock block, 
-        long offsetInBlock, DatanodeInfo dnInfo) {
-      if (offsetInBlock >= block.getNumBytes()) {
-        return null;
-      }
-      try {
-        InetSocketAddress dnAddr = getSocketAddress4Transfer(dnInfo);
-        Token<BlockTokenIdentifier> blockToken = datanode.getBlockAccessToken(
-            block, EnumSet.of(BlockTokenIdentifier.AccessMode.READ));
-        /*
-         * This can be further improved if the replica is local, then we can
-         * read directly from DN and need to check the replica is FINALIZED
-         * state, notice we should not use short-circuit local read which
-         * requires config for domain-socket in UNIX or legacy config in Windows.
-         * The network distance value isn't used for this scenario.
-         */
-        return RemoteBlockReader2.newBlockReader(
-            "dummy", block, blockToken, offsetInBlock, 
-            block.getNumBytes() - offsetInBlock, true,
-            "", newConnectedPeer(block, dnAddr, blockToken, dnInfo), dnInfo,
-            null, cachingStrategy, datanode.getTracer(), -1);
-      } catch (IOException e) {
-        LOG.debug("Exception while creating remote block reader, datanode {}",
-            dnInfo, e);
-        return null;
-      }
-    }
-
-    private Peer newConnectedPeer(ExtendedBlock b, InetSocketAddress addr,
-        Token<BlockTokenIdentifier> blockToken, DatanodeID datanodeId)
-        throws IOException {
-      Peer peer = null;
-      boolean success = false;
-      Socket sock = null;
-      final int socketTimeout = datanode.getDnConf().getSocketTimeout(); 
-      try {
-        sock = NetUtils.getDefaultSocketFactory(conf).createSocket();
-        NetUtils.connect(sock, addr, socketTimeout);
-        peer = DFSUtilClient.peerFromSocketAndKey(datanode.getSaslClient(),
-            sock, datanode.getDataEncryptionKeyFactoryForBlock(b),
-            blockToken, datanodeId, socketTimeout);
-        success = true;
-        return peer;
-      } finally {
-        if (!success) {
-          IOUtils.cleanup(null, peer);
-          IOUtils.closeSocket(sock);
-        }
-      }
-    }
-
-    /**
-     * Send data to targets
-     */
-    private int transferData2Targets(boolean[] targetsStatus) {
-      int nsuccess = 0;
-      for (int i = 0; i < targets.length; i++) {
-        if (targetsStatus[i]) {
-          boolean success = false;
-          try {
-            ByteBuffer buffer = targetBuffers[i];
-            
-            if (buffer.remaining() == 0) {
-              continue;
-            }
-
-            checksum.calculateChunkedSums(
-                buffer.array(), 0, buffer.remaining(), checksumBuf, 0);
-
-            int ckOff = 0;
-            while (buffer.remaining() > 0) {
-              DFSPacket packet = new DFSPacket(packetBuf, maxChunksPerPacket,
-                  blockOffset4Targets[i], seqNo4Targets[i]++, checksumSize, false);
-              int maxBytesToPacket = maxChunksPerPacket * bytesPerChecksum;
-              int toWrite = buffer.remaining() > maxBytesToPacket ?
-                  maxBytesToPacket : buffer.remaining();
-              int ckLen = ((toWrite - 1) / bytesPerChecksum + 1) * checksumSize;
-              packet.writeChecksum(checksumBuf, ckOff, ckLen);
-              ckOff += ckLen;
-              packet.writeData(buffer, toWrite);
-
-              // Send packet
-              packet.writeTo(targetOutputStreams[i]);
-
-              blockOffset4Targets[i] += toWrite;
-              nsuccess++;
-              success = true;
-            }
-          } catch (IOException e) {
-            LOG.warn(e.getMessage());
-          }
-          targetsStatus[i] = success;
-        }
-      }
-      return nsuccess;
-    }
-
-    /**
-     * clear all buffers
-     */
-    private void clearBuffers() {
-      for (StripedReader stripedReader : stripedReaders) {
-        if (stripedReader.buffer != null) {
-          stripedReader.buffer.clear();
-        }
-      }
-
-      if (zeroStripeBuffers != null) {
-        for (ByteBuffer zeroStripeBuffer : zeroStripeBuffers) {
-          zeroStripeBuffer.clear();
-        }
-      }
-
-      for (ByteBuffer targetBuffer : targetBuffers) {
-        if (targetBuffer != null) {
-          targetBuffer.clear();
-        }
-      }
-    }
-
-    // send an empty packet to mark the end of the block
-    private void endTargetBlocks(boolean[] targetsStatus) {
-      for (int i = 0; i < targets.length; i++) {
-        if (targetsStatus[i]) {
-          try {
-            DFSPacket packet = new DFSPacket(packetBuf, 0, 
-                blockOffset4Targets[i], seqNo4Targets[i]++, checksumSize, true);
-            packet.writeTo(targetOutputStreams[i]);
-            targetOutputStreams[i].flush();
-          } catch (IOException e) {
-            LOG.warn(e.getMessage());
-          }
-        }
-      }
-    }
-
-    /**
-     * Initialize  output/input streams for transferring data to target
-     * and send create block request. 
-     */
-    private int initTargetStreams(boolean[] targetsStatus) {
-      int nsuccess = 0;
-      for (int i = 0; i < targets.length; i++) {
-        Socket socket = null;
-        DataOutputStream out = null;
-        DataInputStream in = null;
-        boolean success = false;
-        try {
-          InetSocketAddress targetAddr = 
-              getSocketAddress4Transfer(targets[i]);
-          socket = datanode.newSocket();
-          NetUtils.connect(socket, targetAddr, 
-              datanode.getDnConf().getSocketTimeout());
-          socket.setSoTimeout(datanode.getDnConf().getSocketTimeout());
-
-          ExtendedBlock block = getBlock(blockGroup, targetIndices[i]);
-          Token<BlockTokenIdentifier> blockToken = 
-              datanode.getBlockAccessToken(block,
-                  EnumSet.of(BlockTokenIdentifier.AccessMode.WRITE));
-
-          long writeTimeout = datanode.getDnConf().getSocketWriteTimeout();
-          OutputStream unbufOut = NetUtils.getOutputStream(socket, writeTimeout);
-          InputStream unbufIn = NetUtils.getInputStream(socket);
-          DataEncryptionKeyFactory keyFactory =
-            datanode.getDataEncryptionKeyFactoryForBlock(block);
-          IOStreamPair saslStreams = datanode.getSaslClient().socketSend(
-              socket, unbufOut, unbufIn, keyFactory, blockToken, targets[i]);
-
-          unbufOut = saslStreams.out;
-          unbufIn = saslStreams.in;
-
-          out = new DataOutputStream(new BufferedOutputStream(unbufOut,
-              DFSUtilClient.getSmallBufferSize(conf)));
-          in = new DataInputStream(unbufIn);
-
-          DatanodeInfo source = new DatanodeInfo(datanode.getDatanodeId());
-          new Sender(out).writeBlock(block, targetStorageTypes[i], 
-              blockToken, "", new DatanodeInfo[]{targets[i]}, 
-              new StorageType[]{targetStorageTypes[i]}, source, 
-              BlockConstructionStage.PIPELINE_SETUP_CREATE, 0, 0, 0, 0, 
-              checksum, cachingStrategy, false, false, null);
-
-          targetSockets[i] = socket;
-          targetOutputStreams[i] = out;
-          targetInputStreams[i] = in;
-          nsuccess++;
-          success = true;
-        } catch (Throwable e) {
-          LOG.warn(e.getMessage());
-        } finally {
-          if (!success) {
-            IOUtils.closeStream(out);
-            IOUtils.closeStream(in);
-            IOUtils.closeStream(socket);
-          }
-        }
-        targetsStatus[i] = success;
-      }
-      return nsuccess;
-    }
+  DataNode getDatanode() {
+    return datanode;
   }
 
-  private static class StripedReader {
-    private final short index; // internal block index
-    private BlockReader blockReader;
-    private ByteBuffer buffer;
-    private final ExtendedBlock block;
-    private final DatanodeInfo source;
+  Configuration getConf() {
+    return conf;
+  }
 
-    StripedReader(short index, ExtendedBlock block, DatanodeInfo source) {
-      this.index = index;
-      this.block = block;
-      this.source = source;
-    }
+  ThreadPoolExecutor getStripedReadPool() {
+    return stripedReadPool;
   }
 }

http://git-wip-us.apache.org/repos/asf/hadoop/blob/3c18a53c/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/erasurecode/StripedBlockReader.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/erasurecode/StripedBlockReader.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/erasurecode/StripedBlockReader.java
new file mode 100644
index 0000000..7f71bf7
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/erasurecode/StripedBlockReader.java
@@ -0,0 +1,202 @@
+/**
+ * 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.server.datanode.erasurecode;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.ChecksumException;
+import org.apache.hadoop.hdfs.BlockReader;
+import org.apache.hadoop.hdfs.DFSUtilClient;
+import org.apache.hadoop.hdfs.DFSUtilClient.CorruptedBlocks;
+import org.apache.hadoop.hdfs.RemoteBlockReader2;
+import org.apache.hadoop.hdfs.net.Peer;
+import org.apache.hadoop.hdfs.protocol.DatanodeID;
+import org.apache.hadoop.hdfs.protocol.DatanodeInfo;
+import org.apache.hadoop.hdfs.protocol.ExtendedBlock;
+import org.apache.hadoop.hdfs.security.token.block.BlockTokenIdentifier;
+import org.apache.hadoop.hdfs.server.datanode.DataNode;
+import org.apache.hadoop.io.IOUtils;
+import org.apache.hadoop.net.NetUtils;
+import org.apache.hadoop.security.token.Token;
+import org.slf4j.Logger;
+
+import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.net.Socket;
+import java.nio.ByteBuffer;
+import java.util.EnumSet;
+import java.util.concurrent.Callable;
+
+/**
+ * StripedBlockReader is used to read block data from one source DN, it contains
+ * a block reader, read buffer and striped block index.
+ * Only allocate StripedBlockReader once for one source, and the StripedReader
+ * has the same array order with sources. Typically we only need to allocate
+ * minimum number (minRequiredSources) of StripedReader, and allocate
+ * new for new source DN if some existing DN invalid or slow.
+ * If some source DN is corrupt, set the corresponding blockReader to
+ * null and will never read from it again.
+ */
+@InterfaceAudience.Private
+class StripedBlockReader {
+  private static final Logger LOG = DataNode.LOG;
+
+  private StripedReader stripedReader;
+  private final DataNode datanode;
+  private final Configuration conf;
+
+  private final short index; // internal block index
+  private final ExtendedBlock block;
+  private final DatanodeInfo source;
+  private BlockReader blockReader;
+  private ByteBuffer buffer;
+
+  StripedBlockReader(StripedReader stripedReader, DataNode datanode,
+                     Configuration conf, short index, ExtendedBlock block,
+                     DatanodeInfo source, long offsetInBlock) {
+    this.stripedReader = stripedReader;
+    this.datanode = datanode;
+    this.conf = conf;
+
+    this.index = index;
+    this.source = source;
+    this.block = block;
+
+    BlockReader tmpBlockReader = createBlockReader(offsetInBlock);
+    if (tmpBlockReader != null) {
+      this.blockReader = tmpBlockReader;
+    }
+  }
+
+  ByteBuffer getReadBuffer() {
+    if (buffer == null) {
+      this.buffer = stripedReader.allocateReadBuffer();
+    }
+    return buffer;
+  }
+
+  void resetBlockReader(long offsetInBlock) {
+    this.blockReader = createBlockReader(offsetInBlock);
+  }
+
+  private BlockReader createBlockReader(long offsetInBlock) {
+    if (offsetInBlock >= block.getNumBytes()) {
+      return null;
+    }
+    try {
+      InetSocketAddress dnAddr =
+          stripedReader.getSocketAddress4Transfer(source);
+      Token<BlockTokenIdentifier> blockToken = datanode.getBlockAccessToken(
+          block, EnumSet.of(BlockTokenIdentifier.AccessMode.READ));
+        /*
+         * This can be further improved if the replica is local, then we can
+         * read directly from DN and need to check the replica is FINALIZED
+         * state, notice we should not use short-circuit local read which
+         * requires config for domain-socket in UNIX or legacy config in
+         * Windows. The network distance value isn't used for this scenario.
+         *
+         * TODO: add proper tracer
+         */
+      return RemoteBlockReader2.newBlockReader(
+          "dummy", block, blockToken, offsetInBlock,
+          block.getNumBytes() - offsetInBlock, true,
+          "", newConnectedPeer(block, dnAddr, blockToken, source), source,
+          null, stripedReader.getCachingStrategy(), datanode.getTracer(), -1);
+    } catch (IOException e) {
+      LOG.debug("Exception while creating remote block reader, datanode {}",
+          source, e);
+      return null;
+    }
+  }
+
+  private Peer newConnectedPeer(ExtendedBlock b, InetSocketAddress addr,
+                                Token<BlockTokenIdentifier> blockToken,
+                                DatanodeID datanodeId)
+      throws IOException {
+    Peer peer = null;
+    boolean success = false;
+    Socket sock = null;
+    final int socketTimeout = datanode.getDnConf().getSocketTimeout();
+    try {
+      sock = NetUtils.getDefaultSocketFactory(conf).createSocket();
+      NetUtils.connect(sock, addr, socketTimeout);
+      peer = DFSUtilClient.peerFromSocketAndKey(datanode.getSaslClient(),
+          sock, datanode.getDataEncryptionKeyFactoryForBlock(b),
+          blockToken, datanodeId, socketTimeout);
+      success = true;
+      return peer;
+    } finally {
+      if (!success) {
+        IOUtils.cleanup(null, peer);
+        IOUtils.closeSocket(sock);
+      }
+    }
+  }
+
+  Callable<Void> readFromBlock(final int length,
+                               final CorruptedBlocks corruptedBlocks) {
+    return new Callable<Void>() {
+
+      @Override
+      public Void call() throws Exception {
+        try {
+          getReadBuffer().limit(length);
+          actualReadFromBlock();
+          return null;
+        } catch (ChecksumException e) {
+          LOG.warn("Found Checksum error for {} from {} at {}", block,
+              source, e.getPos());
+          corruptedBlocks.addCorruptedBlock(block, source);
+          throw e;
+        } catch (IOException e) {
+          LOG.info(e.getMessage());
+          throw e;
+        }
+      }
+    };
+  }
+
+  /**
+   * Perform actual reading of bytes from block.
+   */
+  private void actualReadFromBlock() throws IOException {
+    int len = buffer.remaining();
+    int n = 0;
+    while (n < len) {
+      int nread = blockReader.read(buffer);
+      if (nread <= 0) {
+        break;
+      }
+      n += nread;
+    }
+  }
+
+  // close block reader
+  void closeBlockReader() {
+    IOUtils.closeStream(blockReader);
+    blockReader = null;
+  }
+
+  short getIndex() {
+    return index;
+  }
+
+  BlockReader getBlockReader() {
+    return blockReader;
+  }
+}

http://git-wip-us.apache.org/repos/asf/hadoop/blob/3c18a53c/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/erasurecode/StripedBlockWriter.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/erasurecode/StripedBlockWriter.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/erasurecode/StripedBlockWriter.java
new file mode 100644
index 0000000..a62f3c2
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/erasurecode/StripedBlockWriter.java
@@ -0,0 +1,196 @@
+/**
+ * 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.server.datanode.erasurecode;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.StorageType;
+import org.apache.hadoop.hdfs.DFSPacket;
+import org.apache.hadoop.hdfs.DFSUtilClient;
+import org.apache.hadoop.hdfs.protocol.DatanodeInfo;
+import org.apache.hadoop.hdfs.protocol.ExtendedBlock;
+import org.apache.hadoop.hdfs.protocol.datatransfer.BlockConstructionStage;
+import org.apache.hadoop.hdfs.protocol.datatransfer.IOStreamPair;
+import org.apache.hadoop.hdfs.protocol.datatransfer.Sender;
+import org.apache.hadoop.hdfs.protocol.datatransfer.sasl.DataEncryptionKeyFactory;
+import org.apache.hadoop.hdfs.security.token.block.BlockTokenIdentifier;
+import org.apache.hadoop.hdfs.server.datanode.DataNode;
+import org.apache.hadoop.io.IOUtils;
+import org.apache.hadoop.net.NetUtils;
+import org.apache.hadoop.security.token.Token;
+
+import java.io.BufferedOutputStream;
+import java.io.DataInputStream;
+import java.io.DataOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.net.InetSocketAddress;
+import java.net.Socket;
+import java.nio.ByteBuffer;
+import java.util.EnumSet;
+
+/**
+ * A striped block writer that writes reconstructed data to the remote target
+ * datanode.
+ */
+@InterfaceAudience.Private
+class StripedBlockWriter {
+  private final StripedWriter stripedWriter;
+  private final DataNode datanode;
+  private final Configuration conf;
+
+  private final ExtendedBlock block;
+  private final DatanodeInfo target;
+  private final StorageType storageType;
+
+  private Socket targetSocket;
+  private DataOutputStream targetOutputStream;
+  private DataInputStream targetInputStream;
+  private ByteBuffer targetBuffer;
+  private long blockOffset4Target = 0;
+  private long seqNo4Target = 0;
+
+  StripedBlockWriter(StripedWriter stripedWriter, DataNode datanode,
+                     Configuration conf, ExtendedBlock block,
+                     DatanodeInfo target, StorageType storageType)
+      throws IOException {
+    this.stripedWriter = stripedWriter;
+    this.datanode = datanode;
+    this.conf = conf;
+
+    this.block = block;
+    this.target = target;
+    this.storageType = storageType;
+
+    this.targetBuffer = stripedWriter.allocateWriteBuffer();
+
+    init();
+  }
+
+  ByteBuffer getTargetBuffer() {
+    return targetBuffer;
+  }
+
+  /**
+   * Initialize  output/input streams for transferring data to target
+   * and send create block request.
+   */
+  private void init() throws IOException {
+    Socket socket = null;
+    DataOutputStream out = null;
+    DataInputStream in = null;
+    boolean success = false;
+    try {
+      InetSocketAddress targetAddr =
+          stripedWriter.getSocketAddress4Transfer(target);
+      socket = datanode.newSocket();
+      NetUtils.connect(socket, targetAddr,
+          datanode.getDnConf().getSocketTimeout());
+      socket.setSoTimeout(datanode.getDnConf().getSocketTimeout());
+
+      Token<BlockTokenIdentifier> blockToken =
+          datanode.getBlockAccessToken(block,
+              EnumSet.of(BlockTokenIdentifier.AccessMode.WRITE));
+
+      long writeTimeout = datanode.getDnConf().getSocketWriteTimeout();
+      OutputStream unbufOut = NetUtils.getOutputStream(socket, writeTimeout);
+      InputStream unbufIn = NetUtils.getInputStream(socket);
+      DataEncryptionKeyFactory keyFactory =
+          datanode.getDataEncryptionKeyFactoryForBlock(block);
+      IOStreamPair saslStreams = datanode.getSaslClient().socketSend(
+          socket, unbufOut, unbufIn, keyFactory, blockToken, target);
+
+      unbufOut = saslStreams.out;
+      unbufIn = saslStreams.in;
+
+      out = new DataOutputStream(new BufferedOutputStream(unbufOut,
+          DFSUtilClient.getSmallBufferSize(conf)));
+      in = new DataInputStream(unbufIn);
+
+      DatanodeInfo source = new DatanodeInfo(datanode.getDatanodeId());
+      new Sender(out).writeBlock(block, storageType,
+          blockToken, "", new DatanodeInfo[]{target},
+          new StorageType[]{storageType}, source,
+          BlockConstructionStage.PIPELINE_SETUP_CREATE, 0, 0, 0, 0,
+          stripedWriter.getChecksum(), stripedWriter.getCachingStrategy(),
+          false, false, null);
+
+      targetSocket = socket;
+      targetOutputStream = out;
+      targetInputStream = in;
+      success = true;
+    } finally {
+      if (!success) {
+        IOUtils.closeStream(out);
+        IOUtils.closeStream(in);
+        IOUtils.closeStream(socket);
+      }
+    }
+  }
+
+  /**
+   * Send data to targets.
+   */
+  void transferData2Target(byte[] packetBuf) throws IOException {
+    if (targetBuffer.remaining() == 0) {
+      return;
+    }
+
+    stripedWriter.getChecksum().calculateChunkedSums(
+        targetBuffer.array(), 0, targetBuffer.remaining(),
+        stripedWriter.getChecksumBuf(), 0);
+
+    int ckOff = 0;
+    while (targetBuffer.remaining() > 0) {
+      DFSPacket packet = new DFSPacket(packetBuf,
+          stripedWriter.getMaxChunksPerPacket(),
+          blockOffset4Target, seqNo4Target++,
+          stripedWriter.getChecksumSize(), false);
+      int maxBytesToPacket = stripedWriter.getMaxChunksPerPacket()
+          * stripedWriter.getBytesPerChecksum();
+      int toWrite = targetBuffer.remaining() > maxBytesToPacket ?
+          maxBytesToPacket : targetBuffer.remaining();
+      int ckLen = ((toWrite - 1) / stripedWriter.getBytesPerChecksum() + 1)
+          * stripedWriter.getChecksumSize();
+      packet.writeChecksum(stripedWriter.getChecksumBuf(), ckOff, ckLen);
+      ckOff += ckLen;
+      packet.writeData(targetBuffer, toWrite);
+
+      // Send packet
+      packet.writeTo(targetOutputStream);
+
+      blockOffset4Target += toWrite;
+    }
+  }
+
+  // send an empty packet to mark the end of the block
+  void endTargetBlock(byte[] packetBuf) throws IOException {
+    DFSPacket packet = new DFSPacket(packetBuf, 0,
+        blockOffset4Target, seqNo4Target++,
+        stripedWriter.getChecksumSize(), true);
+    packet.writeTo(targetOutputStream);
+    targetOutputStream.flush();
+  }
+
+  void close() {
+    IOUtils.closeStream(targetOutputStream);
+    IOUtils.closeStream(targetInputStream);
+    IOUtils.closeStream(targetSocket);
+  }
+}

http://git-wip-us.apache.org/repos/asf/hadoop/blob/3c18a53c/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/erasurecode/StripedReader.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/erasurecode/StripedReader.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/erasurecode/StripedReader.java
new file mode 100644
index 0000000..fb7699a
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/erasurecode/StripedReader.java
@@ -0,0 +1,466 @@
+/**
+ * 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.server.datanode.erasurecode;
+
+import com.google.common.base.Preconditions;
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.hdfs.DFSConfigKeys;
+import org.apache.hadoop.hdfs.DFSUtilClient.CorruptedBlocks;
+import org.apache.hadoop.hdfs.protocol.DatanodeInfo;
+import org.apache.hadoop.hdfs.protocol.ErasureCodingPolicy;
+import org.apache.hadoop.hdfs.protocol.ExtendedBlock;
+import org.apache.hadoop.hdfs.server.datanode.CachingStrategy;
+import org.apache.hadoop.hdfs.server.datanode.DataNode;
+import org.apache.hadoop.hdfs.server.protocol.BlockECReconstructionCommand.BlockECReconstructionInfo;
+import org.apache.hadoop.hdfs.util.StripedBlockUtil;
+import org.apache.hadoop.hdfs.util.StripedBlockUtil.StripingChunkReadResult;
+import org.apache.hadoop.util.DataChecksum;
+import org.slf4j.Logger;
+
+import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.nio.ByteBuffer;
+import java.util.ArrayList;
+import java.util.BitSet;
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.Callable;
+import java.util.concurrent.CompletionService;
+import java.util.concurrent.Future;
+
+/**
+ * Manage striped readers that performs reading of block data from remote to
+ * serve input data for the erasure decoding.
+ */
+@InterfaceAudience.Private
+class StripedReader {
+  private static final Logger LOG = DataNode.LOG;
+
+  private final int stripedReadTimeoutInMills;
+  private final int stripedReadBufferSize;
+
+  private StripedReconstructor reconstructor;
+  private final DataNode datanode;
+  private final Configuration conf;
+
+  private final int dataBlkNum;
+  private final int parityBlkNum;
+
+
+  private DataChecksum checksum;
+  // Striped read buffer size
+  private int bufferSize;
+  private int[] successList;
+
+  private final int minRequiredSources;
+  // The buffers and indices for striped blocks whose length is 0
+  private ByteBuffer[] zeroStripeBuffers;
+  private short[] zeroStripeIndices;
+
+  // sources
+  private final byte[] liveIndices;
+  private final DatanodeInfo[] sources;
+
+  private final List<StripedBlockReader> readers;
+
+  private final Map<Future<Void>, Integer> futures = new HashMap<>();
+  private final CompletionService<Void> readService;
+
+  StripedReader(StripedReconstructor reconstructor, DataNode datanode,
+                Configuration conf,
+                BlockECReconstructionInfo reconstructionInfo) {
+    stripedReadTimeoutInMills = conf.getInt(
+        DFSConfigKeys.DFS_DN_EC_RECONSTRUCTION_STRIPED_READ_TIMEOUT_MILLIS_KEY,
+        DFSConfigKeys.DFS_DN_EC_RECONSTRUCTION_STRIPED_READ_TIMEOUT_MILLIS_DEFAULT);
+    stripedReadBufferSize = conf.getInt(
+        DFSConfigKeys.DFS_DN_EC_RECONSTRUCTION_STRIPED_READ_BUFFER_SIZE_KEY,
+        DFSConfigKeys.DFS_DN_EC_RECONSTRUCTION_STRIPED_READ_BUFFER_SIZE_DEFAULT);
+
+    this.reconstructor = reconstructor;
+    this.datanode = datanode;
+    this.conf = conf;
+
+    ErasureCodingPolicy ecPolicy = reconstructionInfo.getErasureCodingPolicy();
+    dataBlkNum = ecPolicy.getNumDataUnits();
+    parityBlkNum = ecPolicy.getNumParityUnits();
+
+    ExtendedBlock blockGroup = reconstructionInfo.getExtendedBlock();
+    int cellsNum = (int)((blockGroup.getNumBytes() - 1) / ecPolicy.getCellSize()
+        + 1);
+    minRequiredSources = Math.min(cellsNum, dataBlkNum);
+
+    if (minRequiredSources < dataBlkNum) {
+      int zeroStripNum = dataBlkNum - minRequiredSources;
+      zeroStripeBuffers = new ByteBuffer[zeroStripNum];
+      zeroStripeIndices = new short[zeroStripNum];
+    }
+
+    liveIndices = reconstructionInfo.getLiveBlockIndices();
+    sources = reconstructionInfo.getSourceDnInfos();
+
+    readers = new ArrayList<>(sources.length);
+    readService = reconstructor.createReadService();
+
+    Preconditions.checkArgument(liveIndices.length >= minRequiredSources,
+        "No enough live striped blocks.");
+    Preconditions.checkArgument(liveIndices.length == sources.length,
+        "liveBlockIndices and source datanodes should match");
+  }
+
+  void init() throws IOException {
+    initReaders();
+
+    initBufferSize();
+
+    initZeroStrip();
+  }
+
+  private void initReaders() throws IOException {
+    // Store the array indices of source DNs we have read successfully.
+    // In each iteration of read, the successList list may be updated if
+    // some source DN is corrupted or slow. And use the updated successList
+    // list of DNs for next iteration read.
+    successList = new int[minRequiredSources];
+
+    StripedBlockReader reader;
+    int nSuccess = 0;
+    for (int i = 0; i < sources.length && nSuccess < minRequiredSources; i++) {
+      reader = createReader(i, 0);
+      readers.add(reader);
+      if (reader.getBlockReader() != null) {
+        initOrVerifyChecksum(reader);
+        successList[nSuccess++] = i;
+      }
+    }
+
+    if (nSuccess < minRequiredSources) {
+      String error = "Can't find minimum sources required by "
+          + "reconstruction, block id: "
+          + reconstructor.getBlockGroup().getBlockId();
+      throw new IOException(error);
+    }
+  }
+
+  StripedBlockReader createReader(int idxInSources, long offsetInBlock) {
+    return new StripedBlockReader(this, datanode,
+        conf, liveIndices[idxInSources],
+        reconstructor.getBlock(liveIndices[idxInSources]),
+        sources[idxInSources], offsetInBlock);
+  }
+
+  private void initBufferSize() {
+    int bytesPerChecksum = checksum.getBytesPerChecksum();
+    // The bufferSize is flat to divide bytesPerChecksum
+    int readBufferSize = stripedReadBufferSize;
+    bufferSize = readBufferSize < bytesPerChecksum ? bytesPerChecksum :
+        readBufferSize - readBufferSize % bytesPerChecksum;
+  }
+
+  // init checksum from block reader
+  private void initOrVerifyChecksum(StripedBlockReader reader) {
+    if (checksum == null) {
+      checksum = reader.getBlockReader().getDataChecksum();
+    } else {
+      assert reader.getBlockReader().getDataChecksum().equals(checksum);
+    }
+  }
+
+  protected ByteBuffer allocateReadBuffer() {
+    return ByteBuffer.allocate(getBufferSize());
+  }
+
+  private void initZeroStrip() {
+    if (zeroStripeBuffers != null) {
+      for (int i = 0; i < zeroStripeBuffers.length; i++) {
+        zeroStripeBuffers[i] = reconstructor.allocateBuffer(bufferSize);
+      }
+    }
+
+    BitSet bitset = reconstructor.getLiveBitSet();
+    int k = 0;
+    for (int i = 0; i < dataBlkNum + parityBlkNum; i++) {
+      if (!bitset.get(i)) {
+        if (reconstructor.getBlockLen(i) <= 0) {
+          zeroStripeIndices[k++] = (short)i;
+        }
+      }
+    }
+  }
+
+  private int getReadLength(int index, int reconstructLength) {
+    // the reading length should not exceed the length for reconstruction
+    long blockLen = reconstructor.getBlockLen(index);
+    long remaining = blockLen - reconstructor.getPositionInBlock();
+    return (int) Math.min(remaining, reconstructLength);
+  }
+
+  ByteBuffer[] getInputBuffers(int toReconstructLen) {
+    ByteBuffer[] inputs = new ByteBuffer[dataBlkNum + parityBlkNum];
+
+    for (int i = 0; i < successList.length; i++) {
+      int index = successList[i];
+      StripedBlockReader reader = getReader(index);
+      ByteBuffer buffer = reader.getReadBuffer();
+      paddingBufferToLen(buffer, toReconstructLen);
+      inputs[reader.getIndex()] = (ByteBuffer)buffer.flip();
+    }
+
+    if (successList.length < dataBlkNum) {
+      for (int i = 0; i < zeroStripeBuffers.length; i++) {
+        ByteBuffer buffer = zeroStripeBuffers[i];
+        paddingBufferToLen(buffer, toReconstructLen);
+        int index = zeroStripeIndices[i];
+        inputs[index] = (ByteBuffer)buffer.flip();
+      }
+    }
+
+    return inputs;
+  }
+
+  private void paddingBufferToLen(ByteBuffer buffer, int len) {
+    if (len > buffer.limit()) {
+      buffer.limit(len);
+    }
+    int toPadding = len - buffer.position();
+    for (int i = 0; i < toPadding; i++) {
+      buffer.put((byte) 0);
+    }
+  }
+
+  /**
+   * Read from minimum source DNs required for reconstruction in the iteration.
+   * First try the success list which we think they are the best DNs
+   * If source DN is corrupt or slow, try to read some other source DN,
+   * and will update the success list.
+   *
+   * Remember the updated success list and return it for following
+   * operations and next iteration read.
+   *
+   * @param reconstructLength the length to reconstruct.
+   * @return updated success list of source DNs we do real read
+   * @throws IOException
+   */
+  void readMinimumSources(int reconstructLength) throws IOException {
+    CorruptedBlocks corruptedBlocks = new CorruptedBlocks();
+    try {
+      successList = doReadMinimumSources(reconstructLength, corruptedBlocks);
+    } finally {
+      // report corrupted blocks to NN
+      datanode.reportCorruptedBlocks(corruptedBlocks);
+    }
+  }
+
+  int[] doReadMinimumSources(int reconstructLength,
+                             CorruptedBlocks corruptedBlocks)
+      throws IOException {
+    Preconditions.checkArgument(reconstructLength >= 0 &&
+        reconstructLength <= bufferSize);
+    int nSuccess = 0;
+    int[] newSuccess = new int[minRequiredSources];
+    BitSet usedFlag = new BitSet(sources.length);
+    /*
+     * Read from minimum source DNs required, the success list contains
+     * source DNs which we think best.
+     */
+    for (int i = 0; i < minRequiredSources; i++) {
+      StripedBlockReader reader = readers.get(successList[i]);
+      int toRead = getReadLength(liveIndices[successList[i]],
+          reconstructLength);
+      if (toRead > 0) {
+        Callable<Void> readCallable =
+            reader.readFromBlock(toRead, corruptedBlocks);
+        Future<Void> f = readService.submit(readCallable);
+        futures.put(f, successList[i]);
+      } else {
+        // If the read length is 0, we don't need to do real read
+        reader.getReadBuffer().position(0);
+        newSuccess[nSuccess++] = successList[i];
+      }
+      usedFlag.set(successList[i]);
+    }
+
+    while (!futures.isEmpty()) {
+      try {
+        StripingChunkReadResult result =
+            StripedBlockUtil.getNextCompletedStripedRead(
+                readService, futures, stripedReadTimeoutInMills);
+        int resultIndex = -1;
+        if (result.state == StripingChunkReadResult.SUCCESSFUL) {
+          resultIndex = result.index;
+        } else if (result.state == StripingChunkReadResult.FAILED) {
+          // If read failed for some source DN, we should not use it anymore
+          // and schedule read from another source DN.
+          StripedBlockReader failedReader = readers.get(result.index);
+          failedReader.closeBlockReader();
+          resultIndex = scheduleNewRead(usedFlag,
+              reconstructLength, corruptedBlocks);
+        } else if (result.state == StripingChunkReadResult.TIMEOUT) {
+          // If timeout, we also schedule a new read.
+          resultIndex = scheduleNewRead(usedFlag,
+              reconstructLength, corruptedBlocks);
+        }
+        if (resultIndex >= 0) {
+          newSuccess[nSuccess++] = resultIndex;
+          if (nSuccess >= minRequiredSources) {
+            // cancel remaining reads if we read successfully from minimum
+            // number of source DNs required by reconstruction.
+            cancelReads(futures.keySet());
+            futures.clear();
+            break;
+          }
+        }
+      } catch (InterruptedException e) {
+        LOG.info("Read data interrupted.", e);
+        cancelReads(futures.keySet());
+        futures.clear();
+        break;
+      }
+    }
+
+    if (nSuccess < minRequiredSources) {
+      String error = "Can't read data from minimum number of sources "
+          + "required by reconstruction, block id: " +
+          reconstructor.getBlockGroup().getBlockId();
+      throw new IOException(error);
+    }
+
+    return newSuccess;
+  }
+
+  /**
+   * Schedule a read from some new source DN if some DN is corrupted
+   * or slow, this is called from the read iteration.
+   * Initially we may only have <code>minRequiredSources</code> number of
+   * StripedBlockReader.
+   * If the position is at the end of target block, don't need to do
+   * real read, and return the array index of source DN, otherwise -1.
+   *
+   * @param used the used source DNs in this iteration.
+   * @return the array index of source DN if don't need to do real read.
+   */
+  private int scheduleNewRead(BitSet used, int reconstructLength,
+                              CorruptedBlocks corruptedBlocks) {
+    StripedBlockReader reader = null;
+    // step1: initially we may only have <code>minRequiredSources</code>
+    // number of StripedBlockReader, and there may be some source DNs we never
+    // read before, so will try to create StripedBlockReader for one new source
+    // DN and try to read from it. If found, go to step 3.
+    int m = readers.size();
+    int toRead = 0;
+    while (reader == null && m < sources.length) {
+      reader = createReader(m, reconstructor.getPositionInBlock());
+      readers.add(reader);
+      toRead = getReadLength(liveIndices[m], reconstructLength);
+      if (toRead > 0) {
+        if (reader.getBlockReader() == null) {
+          reader = null;
+          m++;
+        }
+      } else {
+        used.set(m);
+        return m;
+      }
+    }
+
+    // step2: if there is no new source DN we can use, try to find a source
+    // DN we ever read from but because some reason, e.g., slow, it
+    // is not in the success DN list at the begin of this iteration, so
+    // we have not tried it in this iteration. Now we have a chance to
+    // revisit it again.
+    for (int i = 0; reader == null && i < readers.size(); i++) {
+      if (!used.get(i)) {
+        StripedBlockReader stripedReader = readers.get(i);
+        toRead = getReadLength(liveIndices[i], reconstructLength);
+        if (toRead > 0) {
+          stripedReader.closeBlockReader();
+          stripedReader.resetBlockReader(reconstructor.getPositionInBlock());
+          if (stripedReader.getBlockReader() != null) {
+            stripedReader.getReadBuffer().position(0);
+            m = i;
+            reader = stripedReader;
+          }
+        } else {
+          used.set(i);
+          stripedReader.getReadBuffer().position(0);
+          return i;
+        }
+      }
+    }
+
+    // step3: schedule if find a correct source DN and need to do real read.
+    if (reader != null) {
+      Callable<Void> readCallable =
+          reader.readFromBlock(toRead, corruptedBlocks);
+      Future<Void> f = readService.submit(readCallable);
+      futures.put(f, m);
+      used.set(m);
+    }
+
+    return -1;
+  }
+
+  // Cancel all reads.
+  private static void cancelReads(Collection<Future<Void>> futures) {
+    for (Future<Void> future : futures) {
+      future.cancel(true);
+    }
+  }
+
+  void close() {
+    for (StripedBlockReader reader : readers) {
+      reader.closeBlockReader();
+    }
+  }
+
+  StripedBlockReader getReader(int i) {
+    return readers.get(i);
+  }
+
+  int getBufferSize() {
+    return bufferSize;
+  }
+
+  DataChecksum getChecksum() {
+    return checksum;
+  }
+
+  void clearBuffers() {
+    if (zeroStripeBuffers != null) {
+      for (ByteBuffer zeroStripeBuffer : zeroStripeBuffers) {
+        zeroStripeBuffer.clear();
+      }
+    }
+
+    for (StripedBlockReader reader : readers) {
+      if (reader.getReadBuffer() != null) {
+        reader.getReadBuffer().clear();
+      }
+    }
+  }
+
+  InetSocketAddress getSocketAddress4Transfer(DatanodeInfo dnInfo) {
+    return reconstructor.getSocketAddress4Transfer(dnInfo);
+  }
+
+  CachingStrategy getCachingStrategy() {
+    return reconstructor.getCachingStrategy();
+  }
+}


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