org.droolsassert.util

Class ReentrantFileLock

java.lang.Object

java.util.concurrent.locks.ReentrantLock

org.droolsassert.util.ReentrantFileLock

All Implemented Interfaces:

Serializable, Lock

public class ReentrantFileLock
extends ReentrantLock

Combines ReentrantLock with FileLock
Suitable to synchronize threads from different VMs via file system.
As per documentation, file locks are held on behalf of the entire Java virtual machine.
Thus in most cases your ReentrantFileLock should be static to have single JVM instance of the lock object correspond to file lock for the entire JVM.
But it should not be an error to have several exclusive locks on JVM level correspond to single file lock id when you have valid technical usecase to do so.

Inner logic is fairly simple and imply acquiring first java ReentrantLock (fairness option belong here) and, when succeeded, continue further with acquiring file lock.
Release logic behaves in the opposite order.

ReentrantLock is reentrant, meaning the same thread can re-acquire the same lock again (lock held count get incremented).
The same logic implemented for the file lock, meaning any ReentrantFileLock(s) can re-acquire the same lock id on the file running within the same JVM (file lock held count get incremented implying no interaction with file system).
You can also synchronize on resources which are files on file system, like configuration files etc. Files will be locked for write though.

Consider Initialization-on-demand holder idiom for lazy loading

 private static final ReentrantFileLockFactory fileLockFactory = newReentrantFileLockFactory("target/droolsassert/lock");
 private static final ReentrantFileLock consolidatedReportLock = fileLockFactory.newLock(ActivationReportBuilder.class.getName());
 
 
 consolidatedReportLock.lock();
 try {
   ...
 } finally {
   consolidatedReportLock.unlock();
 }
 

See Also:

FileLock, Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	ReentrantFileLock.ReentrantFileLockFactory

Method Summary

Modifier and Type	Method and Description
File	getAbsoluteFile()
void	lock() Unlike other lock methods this one served fairly when enqueued to heavy used file resource.
void	lockInterruptibly()
static ReentrantFileLock.ReentrantFileLockFactory	newReentrantFileLockFactory(boolean fair, File file)
static ReentrantFileLock.ReentrantFileLockFactory	newReentrantFileLockFactory(boolean fair, String filePath)
static ReentrantFileLock.ReentrantFileLockFactory	newReentrantFileLockFactory(File file)
static ReentrantFileLock.ReentrantFileLockFactory	newReentrantFileLockFactory(String filePath)
static ReentrantFileLock.ReentrantFileLockFactory	newReentrantResourceLockFactory(boolean fair, String resourcePath)
static ReentrantFileLock.ReentrantFileLockFactory	newReentrantResourceLockFactory(String resourcePath)
String	toString()
boolean	tryLock()
boolean	tryLock(long timeout, TimeUnit unit)
void	unlock()

Methods inherited from class java.util.concurrent.locks.ReentrantLock

getHoldCount, getOwner, getQueuedThreads, getQueueLength, getWaitingThreads, getWaitQueueLength, hasQueuedThread, hasQueuedThreads, hasWaiters, isFair, isHeldByCurrentThread, isLocked, newCondition

Methods inherited from class java.lang.Object

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

Method Detail

newReentrantFileLockFactory

public static final ReentrantFileLock.ReentrantFileLockFactory newReentrantFileLockFactory(String filePath)

newReentrantFileLockFactory

public static final ReentrantFileLock.ReentrantFileLockFactory newReentrantFileLockFactory(boolean fair,
                                                                                           String filePath)

newReentrantFileLockFactory

public static final ReentrantFileLock.ReentrantFileLockFactory newReentrantFileLockFactory(File file)

newReentrantFileLockFactory

public static final ReentrantFileLock.ReentrantFileLockFactory newReentrantFileLockFactory(boolean fair,
                                                                                           File file)

newReentrantResourceLockFactory

public static final ReentrantFileLock.ReentrantFileLockFactory newReentrantResourceLockFactory(String resourcePath)

newReentrantResourceLockFactory

public static final ReentrantFileLock.ReentrantFileLockFactory newReentrantResourceLockFactory(boolean fair,
                                                                                               String resourcePath)

lock

public void lock()

Unlike other lock methods this one served fairly when enqueued to heavy used file resource.

Specified by:

lock in interface Lock

Overrides:

lock in class ReentrantLock

lockInterruptibly

public void lockInterruptibly()
                       throws InterruptedException

Specified by:

lockInterruptibly in interface Lock

Overrides:

lockInterruptibly in class ReentrantLock

Throws:

InterruptedException

tryLock

public boolean tryLock()

Specified by:

tryLock in interface Lock

Overrides:

tryLock in class ReentrantLock

tryLock

public boolean tryLock(long timeout,
                       TimeUnit unit)
                throws InterruptedException

Specified by:

tryLock in interface Lock

Overrides:

tryLock in class ReentrantLock

Throws:

InterruptedException

unlock

public void unlock()

Specified by:

unlock in interface Lock

Overrides:

unlock in class ReentrantLock

getAbsoluteFile

public File getAbsoluteFile()

toString

public String toString()

Overrides:

toString in class ReentrantLock