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/*************************************************
*
* = PACKAGE
* ACE.Concurrency
*
* = FILENAME
* RWMutex.java
*
*@author Ross Dargahi (rossd@krinfo.com) and Prashant Jain
*
*************************************************/
package ACE.Concurrency;
/*******************************************************************************
* <HR>
* <B> Description </B>
* <BR>
* This class increments a read/write lock. A read/write lock allows multiple
* readers or a single writer to access the guarded element.
* </PRE><P><HR>
* <B> Notes </B>
* <UL>
* <LI> This class does not support recursive semantics
* </UL>
*******************************************************************************/
public class RWMutex
{
/**
* Acquires the write lock
* @exception InterruptedException Lock acquisition interrupted
**/
public void acquire()
throws InterruptedException
{
acquireWrite();
}
/**
* Acquires the read lock
* @exception InterruptedException Lock acquisition interrupted
**/
public synchronized void acquireRead()
throws InterruptedException
{
// Wait till there is an active writer, wait.
while (this.mWriterActive_)
wait();
this.mNumReaders_++;
}
/**
* Acquires the write lock
* @exception InterruptedException Lock acquisition interrupted
**/
public synchronized void acquireWrite()
throws InterruptedException
{
// If there is an active writer before us, then wait for it to finish
// before proceeding
while (this.mWriterActive_)
wait();
// Set the writer active flag to true, then wait for all readers to finish
// with the lock. Note that no new readers will be able to grab the lock
// since they will be blocking on the writer active flag in acquireRead()
this.mWriterActive_ = true;
while (this.mNumReaders_ > 0)
wait();
this.mWriterHoldsLock_ = true;
}
/**
* Release held lock
* @exception InterruptedException Lock acquisition interrupted
**/
public synchronized void release()
{
if (this.mWriterHoldsLock_)
{
this.mWriterActive_ = false;
this.mWriterHoldsLock_ = false;
}
else
{
this.mNumReaders_--;
}
notifyAll();
}
private int mNumReaders_;
// Current number of readers
private boolean mWriterActive_;
// If true, a writer is active
private boolean mWriterHoldsLock_;
// If true, a writer holds the lock
}
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