package org.apache.lucene.store;
/**
* 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.
*/
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;
import java.io.File;
import java.io.RandomAccessFile;
import java.io.IOException;
import java.util.HashSet;
/**
* <p>Implements {@link LockFactory} using native OS file
* locks. Note that because this LockFactory relies on
* java.nio.* APIs for locking, any problems with those APIs
* will cause locking to fail. Specifically, on certain NFS
* environments the java.nio.* locks will fail (the lock can
* incorrectly be double acquired) whereas {@link
* SimpleFSLockFactory} worked perfectly in those same
* environments. For NFS based access to an index, it's
* recommended that you try {@link SimpleFSLockFactory}
* first and work around the one limitation that a lock file
* could be left when the JVM exits abnormally.</p>
*
* <p>The primary benefit of {@link NativeFSLockFactory} is
* that lock files will be properly removed (by the OS) if
* the JVM has an abnormal exit.</p>
*
* <p>Note that, unlike {@link SimpleFSLockFactory}, the existence of
* leftover lock files in the filesystem on exiting the JVM
* is fine because the OS will free the locks held against
* these files even though the files still remain.</p>
*
* <p>If you suspect that this or any other LockFactory is
* not working properly in your environment, you can easily
* test it by using {@link VerifyingLockFactory}, {@link
* LockVerifyServer} and {@link LockStressTest}.</p>
*
* @see LockFactory
*/
public class NativeFSLockFactory extends FSLockFactory {
/**
* Create a NativeFSLockFactory instance, with null (unset)
* lock directory. When you pass this factory to a {@link FSDirectory}
* subclass, the lock directory is automatically set to the
* directory itsself. Be sure to create one instance for each directory
* your create!
*/
public NativeFSLockFactory() throws IOException {
this((File) null);
}
/**
* Create a NativeFSLockFactory instance, storing lock
* files into the specified lockDirName:
*
* @param lockDirName where lock files are created.
*/
public NativeFSLockFactory(String lockDirName) throws IOException {
this(new File(lockDirName));
}
/**
* Create a NativeFSLockFactory instance, storing lock
* files into the specified lockDir:
*
* @param lockDir where lock files are created.
*/
public NativeFSLockFactory(File lockDir) throws IOException {
setLockDir(lockDir);
}
@Override
public synchronized Lock makeLock(String lockName) {
if (lockPrefix != null)
lockName = lockPrefix + "-" + lockName;
return new NativeFSLock(lockDir, lockName);
}
@Override
public void clearLock(String lockName) throws IOException {
// Note that this isn't strictly required anymore
// because the existence of these files does not mean
// they are locked, but, still do this in case people
// really want to see the files go away:
if (lockDir.exists()) {
if (lockPrefix != null) {
lockName = lockPrefix + "-" + lockName;
}
File lockFile = new File(lockDir, lockName);
if (lockFile.exists() && !lockFile.delete()) {
throw new IOException("Cannot delete " + lockFile);
}
}
}
}
class NativeFSLock extends Lock {
private RandomAccessFile f;
private FileChannel channel;
private FileLock lock;
private File path;
private File lockDir;
/*
* The javadocs for FileChannel state that you should have
* a single instance of a FileChannel (per JVM) for all
* locking against a given file. To ensure this, we have
* a single (static) HashSet that contains the file paths
* of all currently locked locks. This protects against
* possible cases where different Directory instances in
* one JVM (each with their own NativeFSLockFactory
* instance) have set the same lock dir and lock prefix.
*/
private static HashSet<String> LOCK_HELD = new HashSet<String>();
public NativeFSLock(File lockDir, String lockFileName) {
this.lockDir = lockDir;
path = new File(lockDir, lockFileName);
}
private synchronized boolean lockExists() {
return lock != null;
}
@Override
public synchronized boolean obtain() throws IOException {
if (lockExists()) {
// Our instance is already locked:
return false;
}
// Ensure that lockDir exists and is a directory.
if (!lockDir.exists()) {
if (!lockDir.mkdirs())
throw new IOException("Cannot create directory: " +
lockDir.getAbsolutePath());
} else if (!lockDir.isDirectory()) {
throw new IOException("Found regular file where directory expected: " +
lockDir.getAbsolutePath());
}
String canonicalPath = path.getCanonicalPath();
boolean markedHeld = false;
try {
// Make sure nobody else in-process has this lock held
// already, and, mark it held if not:
synchronized(LOCK_HELD) {
if (LOCK_HELD.contains(canonicalPath)) {
// Someone else in this JVM already has the lock:
return false;
} else {
// This "reserves" the fact that we are the one
// thread trying to obtain this lock, so we own
// the only instance of a channel against this
// file:
LOCK_HELD.add(canonicalPath);
markedHeld = true;
}
}
try {
f = new RandomAccessFile(path, "rw");
} catch (IOException e) {
// On Windows, we can get intermittent "Access
// Denied" here. So, we treat this as failure to
// acquire the lock, but, store the reason in case
// there is in fact a real error case.
failureReason = e;
f = null;
}
if (f != null) {
try {
channel = f.getChannel();
try {
lock = channel.tryLock();
} catch (IOException e) {
// At least on OS X, we will sometimes get an
// intermittent "Permission Denied" IOException,
// which seems to simply mean "you failed to get
// the lock". But other IOExceptions could be
// "permanent" (eg, locking is not supported via
// the filesystem). So, we record the failure
// reason here; the timeout obtain (usually the
// one calling us) will use this as "root cause"
// if it fails to get the lock.
failureReason = e;
} finally {
if (lock == null) {
try {
channel.close();
} finally {
channel = null;
}
}
}
} finally {
if (channel == null) {
try {
f.close();
} finally {
f = null;
}
}
}
}
} finally {
if (markedHeld && !lockExists()) {
synchronized(LOCK_HELD) {
if (LOCK_HELD.contains(canonicalPath)) {
LOCK_HELD.remove(canonicalPath);
}
}
}
}
return lockExists();
}
@Override
public synchronized void release() throws IOException {
if (lockExists()) {
try {
lock.release();
} finally {
lock = null;
try {
channel.close();
} finally {
channel = null;
try {
f.close();
} finally {
f = null;
synchronized(LOCK_HELD) {
LOCK_HELD.remove(path.getCanonicalPath());
}
}
}
}
// LUCENE-2421: we don't care anymore if the file cannot be deleted
// because it's held up by another process (e.g. AntiVirus). NativeFSLock
// does not depend on the existence/absence of the lock file
path.delete();
} else {
// if we don't hold the lock, and somebody still called release(), for
// example as a result of calling IndexWriter.unlock(), we should attempt
// to obtain the lock and release it. If the obtain fails, it means the
// lock cannot be released, and we should throw a proper exception rather
// than silently failing/not doing anything.
boolean obtained = false;
try {
if (!(obtained = obtain())) {
throw new LockReleaseFailedException(
"Cannot forcefully unlock a NativeFSLock which is held by another indexer component: "
+ path);
}
} finally {
if (obtained) {
release();
}
}
}
}
@Override
public synchronized boolean isLocked() {
// The test for is isLocked is not directly possible with native file locks:
// First a shortcut, if a lock reference in this instance is available
if (lockExists()) return true;
// Look if lock file is present; if not, there can definitely be no lock!
if (!path.exists()) return false;
// Try to obtain and release (if was locked) the lock
try {
boolean obtained = obtain();
if (obtained) release();
return !obtained;
} catch (IOException ioe) {
return false;
}
}
@Override
public String toString() {
return "NativeFSLock@" + path;
}
}