uk.ac.vamsas.client.simpleclient
Class FileLock

java.lang.Object
  uk.ac.vamsas.client.simpleclient.Lock
      uk.ac.vamsas.client.simpleclient.FileLock

public class FileLock

extends Lock

File based Locking mechanism to get around some bizarre limitations of JarEntry seeking. Abstract locks have a target file, to which access is controlled when a lock is held. Native locks on WindowsXP seem to conflict with Jar seek operations, so a file lock creates an advisory lock. Method: A lock file is created, if it doesn't already exist - the naming convention is TargetFile+suffixSeparator+_LockSuffix. A lock is obtained by locking the lock file with a native lock. The NativeLock is used for this.

Author:

JimP

Field Summary

protected static java.lang.String

_LockSuffix

Fields inherited from class uk.ac.vamsas.client.simpleclient.Lock

log, rafile

Constructor Summary

FileLock(java.io.File lockfile, boolean block)

Method Summary

protected void	finalize()
java.io.BufferedOutputStream	getBufferedOutputStream(boolean clear) return buffered output stream to locked file.
java.io.FileInputStream	getFileInputStream(boolean atStart) gets Locked Stream for reading from
java.io.FileOutputStream	getFileOutputStream(boolean clear) gets Locked stream to write to FileInput always starts at the *end* of the file (after any truncation)
java.nio.channels.FileChannel	getRaChannel()
java.io.RandomAccessFile	getRaFile()
boolean	isLocked()
boolean	isTargetLockFile(java.io.File afile) test whether the given file is a target or related to the lock on the target file.
long	length() safe lock target length() function.
void	release() release lock and close all managed channels to file
void	release(boolean closeChannel) optionally close the open random access channel on the file when releasing lock

Methods inherited from class uk.ac.vamsas.client.simpleclient.Lock

getBufferedInputStream

Methods inherited from class java.lang.Object

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

Field Detail

_LockSuffix

protected static java.lang.String _LockSuffix

Constructor Detail

FileLock

public FileLock(java.io.File lockfile,
                boolean block)

Parameters:

lockfile -

block - true means thread blocks until FileLock is obtained.

Method Detail

isLocked

public boolean isLocked()

Specified by:

isLocked in class Lock

Returns:

true if lock is held on the target

release

public void release()

Description copied from class: Lock

release lock and close all managed channels to file

Specified by:

release in class Lock

release

public void release(boolean closeChannel)

Description copied from class: Lock

optionally close the open random access channel on the file when releasing lock

Specified by:

release in class Lock

Parameters:

closeChannel -

getFileInputStream

public java.io.FileInputStream getFileInputStream(boolean atStart)
                                           throws java.io.IOException

Description copied from class: Lock

gets Locked Stream for reading from

Specified by:

getFileInputStream in class Lock

Parameters:

atStart - true to start reading at beginning of file.

Returns:

null if file not locked

Throws:

java.io.IOException

getFileOutputStream

public java.io.FileOutputStream getFileOutputStream(boolean clear)
                                             throws java.io.IOException

Description copied from class: Lock

gets Locked stream to write to FileInput always starts at the *end* of the file (after any truncation)

Specified by:

getFileOutputStream in class Lock

Parameters:

clear - true means file will be cleared to zero length

Returns:

null if file is not locked

Throws:

java.io.IOException

getBufferedOutputStream

public java.io.BufferedOutputStream getBufferedOutputStream(boolean clear)
                                                     throws java.io.IOException

Description copied from class: Lock

return buffered output stream to locked file.

Specified by:

getBufferedOutputStream in class Lock

Parameters:

clear - - true means file is truncated to 0 length before writing

Returns:

Throws:

java.io.IOException

length

public long length()

Description copied from class: Lock

safe lock target length() function.

Specified by:

length in class Lock

Returns:

-1 for non-lockable target, otherwise target's file length

finalize

protected void finalize()
                 throws java.lang.Throwable

Overrides:

finalize in class Lock

Throws:

java.lang.Throwable

getRaFile

public java.io.RandomAccessFile getRaFile()
                                   throws java.io.IOException

Specified by:

getRaFile in class Lock

Throws:

java.io.IOException

getRaChannel

public java.nio.channels.FileChannel getRaChannel()
                                           throws java.io.IOException

Specified by:

getRaChannel in class Lock

Throws:

java.io.IOException

isTargetLockFile

public boolean isTargetLockFile(java.io.File afile)

Description copied from class: Lock

test whether the given file is a target or related to the lock on the target file.

Specified by:

isTargetLockFile in class Lock

Parameters:

afile - a file

Returns:

true if target is locked and afile is related to target