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;
import java.util.Random;
/**
* Implements {@link LockFactory} using native OS file locks
* (available through java.nio.*). Note that for certain
* filesystems native locks are possible but must be
* explicity configured and enabled (and may be disabled by
* default). For example, for NFS servers there sometimes
* must be a separate lockd process running, and other
* configuration may be required such as running the server
* in kernel mode. Other filesystems may not even support
* native OS locks in which case you must use a different
* {@link LockFactory} implementation.
*
* <p>The advantage of this lock factory over
* {@link SimpleFSLockFactory} is that the locks should be
* "correct", whereas {@link SimpleFSLockFactory} uses
* java.io.File.createNewFile which
* <a target="_top" href="http://java.sun.com/j2se/1.4.2/docs/api/java/io/File.html#createNewFile()">has warnings</a> about not
* using it for locking. Furthermore, if the JVM crashes,
* the OS will free any held locks, whereas
* {@link SimpleFSLockFactory} will keep the locks held, requiring
* manual removal before re-running Lucene.</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>Native locks file names have the substring "-n-", which
* you can use to differentiate them from lock files created
* by {@link SimpleFSLockFactory}.</p>
*
* @see LockFactory
*/
public class NativeFSLockFactory extends LockFactory {
/**
* Directory specified by <code>org.apache.lucene.lockDir</code>
* system property. If that is not set, then <code>java.io.tmpdir</code>
* system property is used.
*/
private File lockDir;
// Simple test to verify locking system is "working". On
// NFS, if it's misconfigured, you can hit long (35
// second) timeouts which cause Lock.obtain to take far
// too long (it assumes the obtain() call takes zero
// time). Since it's a configuration problem, we test up
// front once on creating the LockFactory:
private void acquireTestLock() throws IOException {
String randomLockName = "lucene-" + Long.toString(new Random().nextInt(), Character.MAX_RADIX) + "-test.lock";
Lock l = makeLock(randomLockName);
try {
l.obtain();
} catch (IOException e) {
IOException e2 = new IOException("Failed to acquire random test lock; please verify filesystem for lock directory '" + lockDir + "' supports locking");
e2.initCause(e);
throw e2;
}
l.release();
}
/**
* 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 {
this.lockDir = lockDir;
// 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());
}
acquireTestLock();
}
public synchronized Lock makeLock(String lockName) {
if (lockPrefix != null)
lockName = lockPrefix + "-n-" + lockName;
return new NativeFSLock(lockDir, lockName);
}
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 + "-n-" + 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 LOCK_HELD = new HashSet();
public NativeFSLock(File lockDir, String lockFileName) {
this.lockDir = lockDir;
path = new File(lockDir, lockFileName);
}
public synchronized boolean obtain() throws IOException {
if (isLocked()) {
// 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 intermittant "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
// intermittant "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 && !isLocked()) {
synchronized(LOCK_HELD) {
if (LOCK_HELD.contains(canonicalPath)) {
LOCK_HELD.remove(canonicalPath);
}
}
}
}
return isLocked();
}
public synchronized void release() {
try {
if (isLocked()) {
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());
}
}
}
}
path.delete();
}
} catch (IOException e) {
// Not sure how to better message/handle this without
// changing API?
throw new RuntimeException(e);
}
}
public boolean isLocked() {
return lock != null;
}
public String toString() {
return "NativeFSLock@" + path;
}
public void finalize() throws Throwable {
try {
if (isLocked()) {
release();
}
} finally {
super.finalize();
}
}
}
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