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 * has warnings 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.
* *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.
* *Native locks file names have the substring "-n-", which * you can use to differentiate them from lock files created * by {@link SimpleFSLockFactory}.
* * @see LockFactory */ public class NativeFSLockFactory extends LockFactory { /** * Directory specified byorg.apache.lucene.lockDir
* system property. If that is not set, then java.io.tmpdir
* 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();
}
}
}