/**
* Copyright 2016 LinkedIn Corp. All rights reserved.
*
* 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.
*/
package com.github.ambry.utils;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.channels.FileChannel;
import java.nio.channels.OverlappingFileLockException;
/**
* File Lock helper
*/
public class FileLock {
private final File file;
private final FileChannel channel;
private java.nio.channels.FileLock flock = null;
public FileLock(File file) throws FileNotFoundException, IOException {
this.file = file;
file.createNewFile();
channel = new RandomAccessFile(file, "rw").getChannel();
}
/**
* Lock the file or throw an exception if the lock is already held
*/
public void lock() throws IOException {
synchronized (this) {
//trace("Acquiring lock on " + file.getAbsolutePath)
flock = channel.lock();
}
}
/**
* Try to lock the file and return true if the locking succeeds
*/
public boolean tryLock() throws IOException {
synchronized (this) {
// trace("Acquiring lock on " + file.getAbsolutePath)
try {
// weirdly this method will return null if the lock is held by another
// process, but will throw an exception if the lock is held by this process
// so we have to handle both cases
flock = channel.tryLock();
return flock != null;
} catch (OverlappingFileLockException e) {
return false;
}
}
}
/**
* Unlock the lock if it is held
*/
public void unlock() throws IOException {
synchronized (this) {
//trace("Releasing lock on " + file.getAbsolutePath)
if (flock != null) {
flock.release();
}
}
}
/**
* Destroy this lock, closing the associated FileChannel
*/
public void destroy() throws IOException {
synchronized (this) {
unlock();
channel.close();
}
}
}