XORDecoder.java

/**
 * 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.raid;

import java.io.OutputStream;
import java.io.IOException;
import java.util.ArrayList;

import org.apache.hadoop.mapreduce.Mapper.Context;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileStatus;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.hdfs.protocol.Block;
import org.apache.hadoop.raid.StripeStore.StripeInfo;
import org.apache.hadoop.util.Progressable;
import java.util.zip.CRC32;

public class XORDecoder extends Decoder {
  public static final Log LOG = LogFactory.getLog(
                                  "org.apache.hadoop.raid.XORDecoder");

  private int stripeSize;
  public XORDecoder(
    Configuration conf) {
    super(conf, Codec.getCodec("xor"));
    stripeSize = this.codec.stripeLength;
  }

  @Override
  protected long fixErasedBlockImpl(
      FileSystem fs, Path srcFile, FileSystem parityFs, Path parityFile,
      boolean fixSource,
      long blockSize, long errorOffset, long limit, boolean partial, 
      OutputStream out, Context context, CRC32 crc, StripeInfo si,
      boolean recoverFromStripeStore, Block lostBlock)
          throws IOException {
    
    Progressable reporter = context;
    if (reporter == null) {
      reporter = RaidUtils.NULL_PROGRESSABLE;
    }
    
    if (partial) {
      throw new IOException ("We don't support partial reconstruction");
    }
    LOG.info("Fixing block at " + srcFile + ":" + errorOffset +
             ", limit " + limit);
    if (crc != null) {
      crc.reset();
    }
    FileStatus srcStat = fs.getFileStatus(srcFile);
    FSDataInputStream[] inputs = new FSDataInputStream[stripeSize 
                                                       + this.codec.parityLength];

    try {
      long errorBlockOffset = (errorOffset / blockSize) * blockSize;
      long[] srcOffsets = stripeOffsets(errorOffset, blockSize, fixSource);
      for (int i = 0; i < srcOffsets.length; i++) {
        if (fixSource && srcOffsets[i] == errorBlockOffset) {
          inputs[i] = new FSDataInputStream(
            new RaidUtils.ZeroInputStream(blockSize));
          LOG.info("Using zeros at " + srcFile + ":" + errorBlockOffset);
          continue;
        }
        if (srcOffsets[i] < srcStat.getLen()) {
          FSDataInputStream in = fs.open(srcFile);
          in.seek(srcOffsets[i]);
          inputs[i] = in;
        } else {
          inputs[i] = new FSDataInputStream(
            new RaidUtils.ZeroInputStream(blockSize));
          LOG.info("Using zeros at " + srcFile + ":" + errorBlockOffset);
        }
      }

      if (fixSource) {
        FSDataInputStream parityFileIn = parityFs.open(parityFile);
        parityFileIn.seek(parityOffset(errorOffset, blockSize));
        inputs[inputs.length - 1] = parityFileIn;
      } else {
        inputs[inputs.length - 1] = new FSDataInputStream(
            new RaidUtils.ZeroInputStream(blockSize));
        LOG.info("Using zeros at " + parityFile + ":" + errorBlockOffset);
      }
    } catch (IOException e) {
      RaidUtils.closeStreams(inputs);
      throw e;
    }

    int boundedBufferCapacity = 1;
    ParallelStreamReader parallelReader = new ParallelStreamReader(
      reporter, inputs, bufSize, parallelism, boundedBufferCapacity, blockSize);
    parallelReader.start();
    try {
      // Loop while the number of skipped + written bytes is less than the max.
      long written;
      for (written = 0; written < limit; ) {
        ParallelStreamReader.ReadResult readResult;
        try {
          readResult = parallelReader.getReadResult();
        } catch (InterruptedException e) {
          throw new IOException("Interrupted while waiting for read result");
        }
        // Cannot tolerate any IO errors.
        IOException readEx = readResult.getException();
        if (readEx != null) {
          throw readEx;
        }

        int toWrite = (int)Math.min((long)bufSize, limit - written);

        XOREncoder.xor(readResult.readBufs, writeBufs[0]);

        out.write(writeBufs[0], 0, toWrite);
        if (crc != null) {
          crc.update(writeBufs[0], 0, toWrite);
        }
        written += toWrite;
      }
      return written;
    } finally {
      // Inputs will be closed by parallelReader.shutdown().
      parallelReader.shutdown();
    }
  }

  protected long[] stripeOffsets(long errorOffset, long blockSize, 
                                 boolean fixSource) {
    long[] offsets = new long[stripeSize];
    long stripeIdx;
    if (fixSource) {
      stripeIdx = errorOffset / (blockSize * stripeSize);
    } else {
      stripeIdx = errorOffset / blockSize;
    }
    long startOffsetOfStripe = stripeIdx * stripeSize * blockSize;
    for (int i = 0; i < stripeSize; i++) {
      offsets[i] = startOffsetOfStripe + i * blockSize;
    }
    return offsets;
  }

  protected long parityOffset(long errorOffset, long blockSize) {
    long stripeIdx = errorOffset / (blockSize * stripeSize);
    return stripeIdx * blockSize;
  }

}