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ActiveMQ example source code file (ControlFile.java)

This example ActiveMQ source code file (ControlFile.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - ActiveMQ tags/keywords

bytesequence, control, control, controlfile, disable_file_lock, disable_file_lock, file, filelock, io, ioexception, ioexception, overlappingfilelockexception, randomaccessfile, randomaccessfile

The ActiveMQ ControlFile.java source code

/**
 * 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.activemq.kaha.impl.async;

import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.channels.FileLock;
import java.nio.channels.OverlappingFileLockException;

import org.apache.activemq.util.ByteSequence;
import org.apache.activemq.util.IOExceptionSupport;

/**
 * Use to reliably store fixed sized state data. 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.
 * 
 * 
 */
public final class ControlFile {

    private static final boolean DISABLE_FILE_LOCK = "true".equals(System.getProperty("java.nio.channels.FileLock.broken", "false"));
    private final File file;

    /** The File that holds the control data. */
    private final RandomAccessFile randomAccessFile;
    private final int maxRecordSize;
    private final int firstRecordStart;
    private final int secondRecordStart;
    private final int firstRecordEnd;
    private final int secondRecordEnd;

    private long version;
    private FileLock lock;
    private boolean disposed;

    public ControlFile(File file, int recordSize) throws IOException {
        this.file = file;
        this.maxRecordSize = recordSize + 4;
        
        // Calculate where the records start and end.
        this.firstRecordStart = 8;
        this.secondRecordStart = 8 + maxRecordSize + 8 + 8;
        this.firstRecordEnd = firstRecordStart+maxRecordSize;
        this.secondRecordEnd = secondRecordStart+maxRecordSize;

        randomAccessFile = new RandomAccessFile(file, "rw");
    }

    /**
     * Locks the control file.
     * 
     * @throws IOException
     */
    public void lock() throws IOException {
        if (DISABLE_FILE_LOCK) {
            return;
        }

        if (lock == null) {
            try {
                lock = randomAccessFile.getChannel().tryLock(0, randomAccessFile.getChannel().size(), false);
            } catch (OverlappingFileLockException e) {
                throw IOExceptionSupport.create("Control file '" + file + "' could not be locked.",e);
            }
            if (lock == null) {
                throw new IOException("Control file '" + file + "' could not be locked.");
            }
        }
    }

    /**
     * Un locks the control file.
     * 
     * @throws IOException
     */
    public void unlock() throws IOException {
        if (DISABLE_FILE_LOCK) {
            return;
        }

        if (lock != null) {
            lock.release();
            lock = null;
        }
    }

    public void dispose() {
        if (disposed) {
            return;
        }
        disposed = true;
        try {
            unlock();
        } catch (IOException ignore) {
        }
        try {
            randomAccessFile.close();
        } catch (IOException ignore) {
        }
    }

    public synchronized ByteSequence load() throws IOException {
        long l = randomAccessFile.length();
        if (l < maxRecordSize) {
            return null;
        }

        randomAccessFile.seek(firstRecordStart-8);
        long v1 = randomAccessFile.readLong();
        randomAccessFile.seek(firstRecordEnd);
        long v1check = randomAccessFile.readLong();

        randomAccessFile.seek(secondRecordStart - 8);
        long v2 = randomAccessFile.readLong();
        randomAccessFile.seek(secondRecordEnd);
        long v2check = randomAccessFile.readLong();

        byte[] data = null;
        if (v2 == v2check) {
            version = v2;
            randomAccessFile.seek(secondRecordStart);
            int size = randomAccessFile.readInt();
            data = new byte[size];
            randomAccessFile.readFully(data);
        } else if (v1 == v1check) {
            version = v1;
            randomAccessFile.seek(firstRecordStart);
            int size = randomAccessFile.readInt();
            data = new byte[size];
            randomAccessFile.readFully(data);
        } 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 new ByteSequence(data, 0, data.length);
    }

    public void store(ByteSequence data, boolean sync) throws IOException {

        version++;
        randomAccessFile.setLength((maxRecordSize * 2) + 32);
        randomAccessFile.seek(0);

        // Write the first copy of the control data.
        randomAccessFile.writeLong(version);
        randomAccessFile.writeInt(data.getLength());
        randomAccessFile.write(data.getData());
        randomAccessFile.seek(firstRecordEnd);
        randomAccessFile.writeLong(version);

        // Write the second copy of the control data.
        randomAccessFile.writeLong(version);
        randomAccessFile.writeInt(data.getLength());
        randomAccessFile.write(data.getData());
        randomAccessFile.seek(secondRecordEnd);
        randomAccessFile.writeLong(version);

        if (sync) {
            randomAccessFile.getFD().sync();
        }
    }

	public boolean isDisposed() {
		return disposed;
	}

}

Other ActiveMQ examples (source code examples)

Here is a short list of links related to this ActiveMQ ControlFile.java source code file:

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