org.apache.activemq.util.LockFile Maven / Gradle / Ivy
/**
* 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.util;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
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 = Boolean.getBoolean("java.nio.channels.FileLock.broken");
final private File file;
private long lastModified;
private FileLock lock;
private RandomAccessFile randomAccessLockFile;
private int lockCounter;
private final boolean deleteOnUnlock;
private volatile boolean locked;
private String lockSystemPropertyName = "";
private static final Logger LOG = LoggerFactory.getLogger(LockFile.class);
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());
synchronized (LockFile.class) {
lockSystemPropertyName = getVmLockKey();
if (System.getProperty(lockSystemPropertyName) != null) {
throw new IOException("File '" + file + "' could not be locked as lock is already held for this jvm. Value: " + System.getProperty(lockSystemPropertyName));
}
System.setProperty(lockSystemPropertyName, new Date().toString());
}
try {
if (lock == null) {
randomAccessLockFile = new RandomAccessFile(file, "rw");
IOException reason = null;
try {
lock = randomAccessLockFile.getChannel().tryLock(0, Math.max(1, randomAccessLockFile.getChannel().size()), false);
} catch (OverlappingFileLockException e) {
reason = IOExceptionSupport.create("File '" + file + "' could not be locked.", e);
} catch (IOException ioe) {
reason = ioe;
}
if (lock != null) {
//track lastModified only if we are able to successfully obtain the lock.
randomAccessLockFile.writeLong(System.currentTimeMillis());
randomAccessLockFile.getChannel().force(true);
lastModified = file.lastModified();
lockCounter++;
System.setProperty(lockSystemPropertyName, new Date().toString());
locked = true;
} else {
// new read file for next attempt
closeReadFile();
if (reason != null) {
throw reason;
}
throw new IOException("File '" + file + "' could not be locked.");
}
}
} finally {
synchronized (LockFile.class) {
if (lock == null) {
System.getProperties().remove(lockSystemPropertyName);
}
}
}
}
/**
*/
synchronized public void unlock() {
if (DISABLE_FILE_LOCK) {
return;
}
lockCounter--;
if (lockCounter != 0) {
return;
}
// release the lock..
if (lock != null) {
try {
lock.release();
} catch (Throwable ignore) {
} finally {
if (lockSystemPropertyName != null) {
System.getProperties().remove(lockSystemPropertyName);
}
lock = null;
}
}
closeReadFile();
if (locked && deleteOnUnlock) {
file.delete();
}
}
private String getVmLockKey() throws IOException {
return getClass().getName() + ".lock." + file.getCanonicalPath();
}
private void closeReadFile() {
// close the file.
if (randomAccessLockFile != null) {
try {
randomAccessLockFile.close();
} catch (Throwable ignore) {
}
randomAccessLockFile = null;
}
}
/**
* @return true if the lock file's last modified does not match the locally cached lastModified, false otherwise
*/
private boolean hasBeenModified() {
boolean modified = false;
//Create a new instance of the File object so we can get the most up to date information on the file.
File localFile = new File(file.getAbsolutePath());
if (localFile.exists()) {
if(localFile.lastModified() != lastModified) {
LOG.info("Lock file " + file.getAbsolutePath() + ", locked at " + new Date(lastModified) + ", has been modified at " + new Date(localFile.lastModified()));
modified = true;
}
}
else {
//The lock file is missing
LOG.info("Lock file " + file.getAbsolutePath() + ", does not exist");
modified = true;
}
return modified;
}
public boolean keepAlive() {
locked = locked && lock != null && lock.isValid() && !hasBeenModified();
return locked;
}
}