FilePersistence.java

/*
 * Copyright 2014 WANdisco
 *
 *  WANdisco 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 c5db.log;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.file.Path;

import static c5db.log.LogPersistenceService.BytePersistence;
import static java.nio.file.StandardOpenOption.APPEND;
import static java.nio.file.StandardOpenOption.CREATE;
import static java.nio.file.StandardOpenOption.READ;

/**
 * A BytePersistence using a File, accessed by FileChannels.
 */
public class FilePersistence implements BytePersistence {
  private final FileChannel appendChannel;
  final Path path;
  private long filePosition;

  public FilePersistence(Path path) throws IOException {
    this.path = path;
    appendChannel = FileChannel.open(path, CREATE, APPEND);
    filePosition = appendChannel.position();
  }

  @Override
  public boolean isEmpty() throws IOException {
    return filePosition == 0;
  }

  @Override
  public long size() throws IOException {
    return filePosition;
  }

  @Override
  public void append(ByteBuffer[] buffers) throws IOException {
    appendChannel.write(buffers);
    filePosition += totalBytesToBeWritten(buffers);
  }

  @Override
  public LogPersistenceService.PersistenceReader getReader() throws IOException {
    return new NioReader(FileChannel.open(path, READ));
  }

  @Override
  public void truncate(long size) throws IOException {
    if (size > this.size()) {
      throw new IllegalArgumentException("Truncation may not grow the file");
    }
    appendChannel.truncate(size);
    filePosition = size;
  }

  @Override
  public void sync() throws IOException {
    appendChannel.force(true);
  }

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

  // TODO This should be done once, in one central place
  private long totalBytesToBeWritten(ByteBuffer[] buffers) {
    long sum = 0;
    for (ByteBuffer b : buffers) {
      sum += b.position();
    }
    return sum;
  }

  private static class NioReader implements LogPersistenceService.PersistenceReader {
    private final FileChannel fileChannel;

    public NioReader(FileChannel fileChannel) {
      this.fileChannel = fileChannel;
    }

    @Override
    public long position() throws IOException {
      return fileChannel.position();
    }

    public void position(long newPos) throws IOException {
      fileChannel.position(newPos);
    }

    @Override
    public int read(ByteBuffer dst) throws IOException {
      return fileChannel.read(dst);
    }

    @Override
    public boolean isOpen() {
      return fileChannel.isOpen();
    }

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