LocalFileTransactionLog.java

/*
 * Copyright © 2012-2014 Cask Data, Inc.
 *
 * Licensed 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 co.cask.tephra.persist;

import co.cask.tephra.metrics.MetricsCollector;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.EOFException;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;

/**
 * Reads and writes transaction logs against files in the local filesystem.
 */
public class LocalFileTransactionLog extends AbstractTransactionLog {
  private final File logFile;

  /**
   * Creates a new transaction log using the given file instance.
   * @param logFile The log file to use.
   */
  public LocalFileTransactionLog(File logFile, long timestamp, MetricsCollector metricsCollector) {
    super(timestamp, metricsCollector);
    this.logFile = logFile;
  }

  @Override
  public String getName() {
    return logFile.getAbsolutePath();
  }

  @Override
  protected TransactionLogWriter createWriter() throws IOException {
    return new LogWriter(logFile);
  }

  @Override
  public TransactionLogReader getReader() throws IOException {
    return new LogReader(logFile);
  }

  private static final class LogWriter implements TransactionLogWriter {
    private final FileOutputStream fos;
    private final DataOutputStream out;

    public LogWriter(File logFile) throws IOException {
      this.fos = new FileOutputStream(logFile);
      this.out = new DataOutputStream(new BufferedOutputStream(fos, LocalFileTransactionStateStorage.BUFFER_SIZE));
    }

    @Override
    public void append(Entry entry) throws IOException {
      entry.write(out);
    }

    @Override
    public void commitMarker(int count) throws IOException {
      // skip for local file
    }

    @Override
    public void sync() throws IOException {
      out.flush();
    }

    @Override
    public void close() throws IOException {
      out.flush();
      out.close();
      fos.close();
    }
  }

  private static final class LogReader implements TransactionLogReader {
    private final FileInputStream fin;
    private final DataInputStream in;
    private Entry reuseEntry = new Entry();

    public LogReader(File logFile) throws IOException {
      this.fin = new FileInputStream(logFile);
      this.in = new DataInputStream(new BufferedInputStream(fin, LocalFileTransactionStateStorage.BUFFER_SIZE));
    }

    @Override
    public TransactionEdit next() throws IOException {
      Entry entry = new Entry();
      try {
        entry.readFields(in);
      } catch (EOFException eofe) {
        // signal end of file by returning null
        return null;
      }
      return entry.getEdit();
    }

    @Override
    public TransactionEdit next(TransactionEdit reuse) throws IOException {
      try {
        reuseEntry.getKey().readFields(in);
        reuse.readFields(in);
      } catch (EOFException eofe) {
        // signal end of file by returning null
        return null;
      }
      return reuse;
    }

    @Override
    public void close() throws IOException {
      in.close();
      fin.close();
    }
  }
}