/*
* Copyright 2002-2016 the original author or authors.
*
* 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.springframework.integration.file.locking;
import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;
import java.nio.channels.OverlappingFileLockException;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
/**
* Static cache of FileLocks that can be used to ensure that only a single lock is used inside this ClassLoader.
*
* @author Iwein Fuld
* @author Gary Russell
* @since 2.0
*/
final class FileChannelCache {
private static ConcurrentMap<File, FileChannel> channelCache = new ConcurrentHashMap<File, FileChannel>();
private FileChannelCache() {
super();
}
/**
* Try to get a lock for this file while guaranteeing that the same channel will be used for all file locks in this
* VM. If the lock could not be acquired this method will return <code>null</code>.
* <p>
* Locks acquired through this method should be passed back to #closeChannelFor to prevent memory leaks.
* <p>
* Thread safe.
*/
public static FileLock tryLockFor(File fileToLock) throws IOException {
FileChannel channel = channelCache.get(fileToLock);
if (channel == null) {
@SuppressWarnings("resource")
FileChannel newChannel = new RandomAccessFile(fileToLock, "rw").getChannel();
FileChannel original = channelCache.putIfAbsent(fileToLock, newChannel);
if (original != null) {
channel = original;
try {
newChannel.close();
}
catch (IOException e) {
// ignore
}
}
else {
channel = newChannel;
}
}
FileLock lock = null;
if (channel != null) {
try {
lock = channel.tryLock();
}
catch (OverlappingFileLockException e) {
// File is already locked in this thread or virtual machine
}
}
return lock;
}
/**
* Close the channel for the file passed in.
* <p>
* Thread safe.
*/
public static void closeChannelFor(File fileToUnlock) {
FileChannel fileChannel = channelCache.remove(fileToUnlock);
if (fileChannel != null) {
try {
fileChannel.close();
}
catch (IOException e) {
// ignore
}
}
}
public static boolean isLocked(File file) {
return channelCache.containsKey(file);
}
}