/**
*
* Copyright 2004 Hiram Chirino
*
* 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 org.activeio.journal.active;
import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;
import org.activeio.Disposable;
import org.activeio.Packet;
import org.activeio.packet.ByteBufferPacket;
/**
* Control file holds the last known good state of the journal. It stores the state in
* record that is versioned and repeated twice in the file so that a failure in the
* middle of the write of the first or second record do not not result in an unknown
* state.
*
* @version $Revision: 1.1 $
*/
final public class ControlFile implements Disposable {
/** The File that holds the control data. */
private final RandomAccessFile file;
private final FileChannel channel;
private final ByteBufferPacket controlData;
private long controlDataVersion=0;
private FileLock lock;
private boolean disposed;
public ControlFile(File fileName, int controlDataSize) throws IOException {
boolean existed = fileName.exists();
file = new RandomAccessFile(fileName, "rw");
channel = file.getChannel();
controlData = new ByteBufferPacket(ByteBuffer.allocateDirect(controlDataSize));
}
/**
* Locks the control file.
* @throws IOException
*/
public void lock() throws IOException {
if( lock==null ) {
lock = channel.tryLock();
if( lock ==null )
throw new IOException("Journal is allready opened by another application");
}
}
/**
* Un locks the control file.
* @throws IOException
*/
public void unlock() throws IOException {
if( lock != null ) {
lock.release();
lock=null;
}
}
public boolean load() throws IOException {
long l = file.length();
if( l < controlData.capacity() ) {
controlDataVersion=0;
controlData.position(0);
controlData.limit(0);
return false;
} else {
file.seek(0);
long v1 = file.readLong();
file.seek(controlData.capacity()+8);
long v1check = file.readLong();
file.seek(controlData.capacity()+16);
long v2 = file.readLong();
file.seek((controlData.capacity()*2)+24);
long v2check = file.readLong();
if( v2 == v2check ) {
controlDataVersion = v2;
file.seek(controlData.capacity()+24);
controlData.clear();
channel.read(controlData.getByteBuffer());
} else if ( v1 == v1check ){
controlDataVersion = v1;
file.seek(controlData.capacity()+8);
controlData.clear();
channel.read(controlData.getByteBuffer());
} else {
// Bummer.. Both checks are screwed. we don't know
// if any of the two buffer are ok. This should
// only happen is data got corrupted.
throw new IOException("Control data corrupted.");
}
return true;
}
}
public void store() throws IOException {
controlDataVersion++;
file.setLength((controlData.capacity()*2)+32);
file.seek(0);
// Write the first copy of the control data.
file.writeLong(controlDataVersion);
controlData.clear();
channel.write(controlData.getByteBuffer());
file.writeLong(controlDataVersion);
// Write the second copy of the control data.
file.writeLong(controlDataVersion);
controlData.clear();
channel.write(controlData.getByteBuffer());
file.writeLong(controlDataVersion);
channel.force(false);
}
public Packet getControlData() {
controlData.clear();
return controlData;
}
public void dispose() {
if( disposed )
return;
disposed=true;
try {
unlock();
} catch (IOException e) {
}
try {
file.close();
} catch (IOException e) {
}
}
}