uk.org.ogsadai.common.files
Class FileLock

java.lang.Object
  |
  +--uk.org.ogsadai.common.files.FileLock

public class FileLock

extends java.lang.Object

This class implements a Multiple Reader, Single Writer (MRSW) mutual exclusion locking facility.

Threads wishing to obtain a lock on a file should call getReadLock or getWriteLock, and should call returnReadLock or returnWriteLock to relinquish the lock.

The MRSW lock permits either one thread to hold a write lock, or any number of threads to hold read locks. For example, if two threads have read locks and another thread calls getWriteLock to obtain a write lock, this thread waits until both reading threads have relinquished their read locks via returnReadLock.

Author:

The OGSA-DAI Project Team

Field Summary

private static java.lang.String	COPYRIGHT_NOTICE
private static DAILogger	LOG
private java.util.Map	readers
private java.util.Map	writers

Constructor Summary

FileLock()

Method Summary

private java.lang.String	canonical(java.lang.String fileName) Return the canonical version of the given filename, if at all possible.
int	countReaders(java.lang.String fileName) Return the number of threads with a read lock on a file.
int	countWriters(java.lang.String fileName) Return the number of threads with a write lock on a file.
private void	decrementReaders(java.lang.String fileName) Decrement the number of threads with a read lock on a file.
private void	decrementWriters(java.lang.String fileName) Decrement the number of threads with a write lock on a file.
void	doLocking(java.lang.String fileName, boolean lock, boolean read) Perform a locking or unlocking operation on a file.
void	getReadLock(java.lang.String fileName) Block until a read lock is available on a file, and obtain it.
void	getWriteLock(java.lang.String fileName) Block until a write lock is available on a file, and obtain it.
private void	incrementReaders(java.lang.String fileName) Increment the number of threads with a read lock on a file.
private void	incrementWriters(java.lang.String fileName) Increment the number of threads with a write lock on a file.
void	returnReadLock(java.lang.String fileName) Relinquish a read lock on a file.
void	returnWriteLock(java.lang.String fileName) Relinquish a write lock on a file.
private void	setReaders(java.lang.String fileName, int number) Set the number of threads with a read lock on a file.
private void	setWriters(java.lang.String fileName, int number) Set the number of threads with a write lock on a file.

Methods inherited from class java.lang.Object

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

Field Detail

COPYRIGHT_NOTICE

private static final java.lang.String COPYRIGHT_NOTICE

See Also:

Constant Field Values

LOG

private static DAILogger LOG

readers

private java.util.Map readers

writers

private java.util.Map writers

Constructor Detail

FileLock

public FileLock()

Method Detail

doLocking

public void doLocking(java.lang.String fileName,
                      boolean lock,
                      boolean read)
               throws FileLockException

Perform a locking or unlocking operation on a file.

Parameters:

fileName - Name of file.

lock - true to lock the file, false to unlock the file

read - true if the lock is a read lock, false if the lock is a write lock

Throws:

FileLockException - if an error occurs while waiting for a lock.

getReadLock

public void getReadLock(java.lang.String fileName)
                 throws FileLockException

Block until a read lock is available on a file, and obtain it.

Parameters:

fileName - Name of file.

Throws:

FileLockException - if an error occurs while waiting for the lock.

returnReadLock

public void returnReadLock(java.lang.String fileName)
                    throws NoExistingFileLockException

Relinquish a read lock on a file.

Parameters:

fileName - Name of file.

Throws:

NoExistingFileLockException - if there is no existing read lock.

getWriteLock

public void getWriteLock(java.lang.String fileName)
                  throws FileLockException

Block until a write lock is available on a file, and obtain it.

Parameters:

fileName - Name of file.

Throws:

FileLockException - if an error occurs while waiting for the lock.

returnWriteLock

public void returnWriteLock(java.lang.String fileName)
                     throws NoExistingFileLockException

Relinquish a write lock on a file.

Parameters:

fileName - Name of file.

Throws:

NoExistingFileLockException - if there is no existing write lock.

countReaders

public int countReaders(java.lang.String fileName)

Return the number of threads with a read lock on a file.

Parameters:

fileName - Name of file.

Returns:

the number of readers

countWriters

public int countWriters(java.lang.String fileName)

Return the number of threads with a write lock on a file.

Parameters:

fileName - Name of file.

Returns:

the number of writers

setReaders

private void setReaders(java.lang.String fileName,
                        int number)

Set the number of threads with a read lock on a file.

Parameters:

fileName - Name of file.

number - Number of readers.

setWriters

private void setWriters(java.lang.String fileName,
                        int number)

Set the number of threads with a write lock on a file.

Parameters:

fileName - Name of file.

number - Number of writers.

incrementReaders

private void incrementReaders(java.lang.String fileName)

Increment the number of threads with a read lock on a file.

Parameters:

fileName - Name of file.

decrementReaders

private void decrementReaders(java.lang.String fileName)

Decrement the number of threads with a read lock on a file.

Parameters:

fileName - Name of file.

Throws:

NoExistingFileLockException - if there is no existing read lock.

incrementWriters

private void incrementWriters(java.lang.String fileName)

Increment the number of threads with a write lock on a file.

Parameters:

fileName - Name of file.

decrementWriters

private void decrementWriters(java.lang.String fileName)

Decrement the number of threads with a write lock on a file.

Parameters:

fileName - Name of file.

Throws:

NoExistingFileLockException - if there is no existing write lock.

canonical

private java.lang.String canonical(java.lang.String fileName)

Return the canonical version of the given filename, if at all possible.

Parameters:

fileName - Name of file.

Returns:

the canonical filename