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ActiveMQ example source code file (LockFile.java)

This example ActiveMQ source code file (LockFile.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

disable_file_lock, disable_file_lock, file, file, filelock, io, ioexception, ioexception, lockfile, overlappingfilelockexception, randomaccessfile, randomaccessfile, string, throwable, util

The ActiveMQ LockFile.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.kahadb.util;

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

/**
 * Used to lock a File.
 * 
 * @author chirino
 */
public class LockFile {
    
    private static final boolean DISABLE_FILE_LOCK = "true".equals(System.getProperty("java.nio.channels.FileLock.broken", "false"));
    final private File file;
    
    private FileLock lock;
    private RandomAccessFile readFile;
    private int lockCounter;
    private final boolean deleteOnUnlock;
    
    public LockFile(File file, boolean deleteOnUnlock) {
        this.file = file;
        this.deleteOnUnlock = deleteOnUnlock;
    }

    /**
     * @throws IOException
     */
    synchronized public void lock() throws IOException {
        if (DISABLE_FILE_LOCK) {
            return;
        }

        if( lockCounter>0 ) {
            return;
        }
        
        IOHelper.mkdirs(file.getParentFile());
        if (System.getProperty(getVmLockKey()) != null) {
            throw new IOException("File '" + file + "' could not be locked as lock is already held for this jvm.");
        }
        if (lock == null) {
            readFile = new RandomAccessFile(file, "rw");
            IOException reason = null;
            try {
                lock = readFile.getChannel().tryLock(0, readFile.getChannel().size(), false);
            } catch (OverlappingFileLockException e) {
                reason = IOExceptionSupport.create("File '" + file + "' could not be locked.",e);
            } catch (IOException ioe) {
                reason = ioe;
            }
            if (lock != null) {
                lockCounter++;
                System.setProperty(getVmLockKey(), new Date().toString());
            } else {
                // new read file for next attempt
                closeReadFile();
                if (reason != null) {
                    throw reason;
                }
                throw new IOException("File '" + file + "' could not be locked.");
            }
              
        }
    }

    /**
     */
    public void unlock() {
        if (DISABLE_FILE_LOCK) {
            return;
        }
        
        lockCounter--;
        if( lockCounter!=0 ) {
            return;
        }
        
        // release the lock..
        if (lock != null) {
            try {
                lock.release();
                System.getProperties().remove(getVmLockKey());
            } catch (Throwable ignore) {
            }
            lock = null;
        }
        closeReadFile();
        
        if( deleteOnUnlock ) {
            file.delete();
        }
    }

    private String getVmLockKey() throws IOException {
        return getClass().getName() + ".lock." + file.getCanonicalPath();
    }

    private void closeReadFile() {
        // close the file.
        if (readFile != null) {
            try {
                readFile.close();
            } catch (Throwable ignore) {
            }
            readFile = null;
        }
        
    }

}

Other ActiveMQ examples (source code examples)

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

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