com.googlecode.fascinator.common.DummyFileLock Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of fascinator-common Show documentation
There is a newer version: 1.6
/*
 * The Fascinator - Dummy File Lock
 * Copyright (C) 2008-2010 University of Southern Queensland
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

package com.googlecode.fascinator.common;

import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;
import java.nio.channels.OverlappingFileLockException;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * A basic file lock against a local file. For practical purposes it's often
 * best to do logic checking against a seperate '.lock' file so that other code
 * (such as a properties parser) doesn't get mixed up with a lock on your 'real'
 * file.
 * 
 * @author Greg Pendlebury
 */
public class DummyFileLock {
    private String file_name;
    private FileOutputStream file;
    private FileChannel fileChannel;
    private FileLock lock;
    private Logger log = LoggerFactory.getLogger(DummyFileLock.class);

    /**
     * Creates a new lock against the file provided.
     * 
     */
    public DummyFileLock(String new_file) throws IOException {
        file_name = new_file;
    }

    /**
     * Get Lock status of a file
     * 
     * @throws IOException
     */
    public void getLock() throws IOException {
        file = new FileOutputStream(file_name);
        fileChannel = file.getChannel();
        int lockTimeout = 0;
        int lockSleepTime = 500;

        try {
            // Try to get the lock
            lock = fileChannel.lock();

            // If it's already locked
        } catch (OverlappingFileLockException e) {
            try {
                // Check for timeout
                lockTimeout += lockSleepTime;
                if (lockTimeout > 60000) {
                    log
                            .error("File Lock Timeout error : Waited more then 60s for access to : "
                                    + file_name);
                    fileChannel.close();
                    file.close();
                } else {
                    // Go to sleep briefly
                    Thread.sleep(lockSleepTime);
                    // Try again
                    getLock();
                }
            } catch (InterruptedException ex) {
                // We've been woken up early
                throw new IOException(
                        "Interrupted waiting for lock! Terminating.");
            }
        }
    }

    /**
     * Release lock of the file
     * 
     * @throws IOException if File not found
     */
    public void release() throws IOException {
        if (lock.isValid()) {
            lock.release();
        }
        if (fileChannel.isOpen()) {
            fileChannel.close();
            file.close();
        }
    }
}