Package com.norconex.commons.lang.file

Class FileLocker

java.lang.Object

com.norconex.commons.lang.file.FileLocker

public class FileLocker
extends Object

Simple FileLock wrapper to use operating-system file-locking ability to help with multi-processes management. No instance of the file being locked is returned by this class. It's main purpose is to prevent other processes from trying to acquire a lock when it is not desirable to do so. For instance, it can be used as a way to guarantee only one instance of a specific process can run per operating system and file system.

The lock(), tryLock(), and unlock() are similar to FileChannel.lock(), FileChannel.tryLock(), and FileLock.release() but with slightly different behaviors. Refer to the corresponding method documentation for more detail.

Since:

2.0.0

Author:

Pascal Essiembre

Constructor Summary

Constructors

Constructor	Description
FileLocker(Path lockFile)

Method Summary

Modifier and Type	Method	Description
boolean	isLocked()	Gets whether the file is locked.
void	lock()	Locks the unlocked file.
void	lock(boolean block)	Locks the unlocked file.
String	toString()
boolean	tryLock()	Tries to locks the unlocked file and returns true when successful.
void	unlock()	Unlocks the locked file.

Methods inherited from class java.lang.Object

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

Constructor Detail

FileLocker

public FileLocker(Path lockFile)

Method Detail

tryLock

public boolean tryLock()
                throws IOException

Tries to locks the unlocked file and returns true when successful. If the file does not exist, an empty file is created. If the file exists and is already locked, this method silently fails and returns false.

Returns:

true if file was successfully locked.

Throws:

IOException - could not lock

See Also:

lock()

lock

public void lock()
          throws IOException

Locks the unlocked file. If the file does not exist, an empty file is created. If the file exists and is already locked, this method throws a FileAlreadyLockedException.

Contrary to FileChannel.lock(), this method does not block by default. To have it block and wait for a lock to be free, use lock(boolean) with true instead.

Throws:

IOException - could not lock

See Also:

tryLock()

lock

public void lock(boolean block)
          throws IOException

Locks the unlocked file. If the file does not exist, an empty file is created. If the file exists and is already locked, this method throws a FileAlreadyLockedException.

Parameters:

block - set to true to wait for an available lock

Throws:

IOException - could not lock

unlock

public void unlock()
            throws IOException

Unlocks the locked file. Unlocking an inexistent or already unlocked file has no effect.

Throws:

IOException - could not unlock

isLocked

public boolean isLocked()

Gets whether the file is locked.

Returns:

true if locked.

toString

public String toString()

Overrides:

toString in class Object