org.modeshape.jcr.value.binary
Class FileLocks

java.lang.Object
  org.modeshape.jcr.value.binary.FileLocks

public final class FileLocks
extends Object

A utility class that represents read and write lock for files, which internally uses FileLock to coordinate file locks with other processes. This class maintains a single file lock per file, since multiple concurrent FileLocks on the same file are not allowed by the JVM. It also uses reference counts to remove locks only when a named lock is no longer being used.

Nested Class Summary

protected class	FileLocks.LockHolder
protected static class	FileLocks.WrappedLock

Method Summary

static FileLocks	get() Obtain the singleton instance for this virtual machine.
protected FileLocks.WrappedLock	lock(File file, boolean writeLock, boolean block)
FileLocks.WrappedLock	readLock(File file) Obtain a read lock for the supplied file.
int	size() Get the number of named locks.
FileLocks.WrappedLock	tryReadLock(File file) Try to obtain a read lock for the supplied file.
FileLocks.WrappedLock	tryWriteLock(File file) Try to obtain a write lock for the supplied file.
protected void	unlock(FileLocks.LockHolder holder, Lock rawLock)
FileLocks.WrappedLock	writeLock(File file) Obtain a write lock for the supplied file.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

get

public static FileLocks get()

Obtain the singleton instance for this virtual machine.

Returns:

the file lock manager; never null

writeLock

public FileLocks.WrappedLock writeLock(File file)
                                throws IOException

Obtain a write lock for the supplied file. When this method returns, the current thread will have obtained the lock. Therefore, there is no need to call any of the lock methods (e.g., FileLocks.WrappedLock.lock(), FileLocks.WrappedLock.lockInterruptibly(), FileLocks.WrappedLock.tryLock() or FileLocks.WrappedLock.tryLock(long, TimeUnit)), as those methods will immediately return.

Parameters:

file - the file to be locked; may not be null

Returns:

the lock held by the current thread; never null

Throws:

IOException - if there is a problem obtaining the file lock

readLock

public FileLocks.WrappedLock readLock(File file)
                               throws IOException

Obtain a read lock for the supplied file. When this method returns, the current thread will have obtained the lock. Therefore, there is no need to call any of the lock methods (e.g., FileLocks.WrappedLock.lock(), FileLocks.WrappedLock.lockInterruptibly(), FileLocks.WrappedLock.tryLock() or FileLocks.WrappedLock.tryLock(long, TimeUnit)), as those methods will immediately return.

Parameters:

file - the file to be locked; may not be null

Returns:

the lock held by the current thread; never null

Throws:

IOException - if there is a problem obtaining the file lock

tryWriteLock

public FileLocks.WrappedLock tryWriteLock(File file)
                                   throws IOException

Try to obtain a write lock for the supplied file. When this method returns a non-null lock, the current thread will have obtained the lock. Therefore, there is no need to call any of the lock methods (e.g., FileLocks.WrappedLock.lock(), FileLocks.WrappedLock.lockInterruptibly(), FileLocks.WrappedLock.tryLock() or FileLocks.WrappedLock.tryLock(long, TimeUnit)), as those methods will immediately return.

However, if this method returns null, this method could not obtain the lock.

Parameters:

file - the file to be locked; may not be null

Returns:

the lock held by the current thread; null if the lock could not be obtained

Throws:

IOException - if there is a problem obtaining the file lock

tryReadLock

public FileLocks.WrappedLock tryReadLock(File file)
                                  throws IOException

Try to obtain a read lock for the supplied file. When this method returns a non-null lock, the current thread will have obtained the lock. Therefore, there is no need to call any of the lock methods (e.g., FileLocks.WrappedLock.lock(), FileLocks.WrappedLock.lockInterruptibly(), FileLocks.WrappedLock.tryLock() or FileLocks.WrappedLock.tryLock(long, TimeUnit)), as those methods will immediately return.

However, if this method returns null, this method could not obtain the lock.

Parameters:

file - the file to be locked; may not be null

Returns:

the lock held by the current thread; null if the lock could not be obtained

Throws:

IOException - if there is a problem obtaining the file lock

lock

protected final FileLocks.WrappedLock lock(File file,
                                           boolean writeLock,
                                           boolean block)
                                    throws IOException

Throws:

IOException

unlock

protected void unlock(FileLocks.LockHolder holder,
                      Lock rawLock)

size

public int size()

Get the number of named locks.

Returns:

the number of named locks; never negative