/*******************************************************************************
* Copyright (c) 2000, 2006 IBM Corporation and others.
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Contributors:
* IBM Corporation - initial API and implementation
*******************************************************************************/
package com.aptana.ide.internal.index.core;
/**
* Monitor ensuring no more than one writer working concurrently. Multiple readers are allowed to perform
* simultaneously.
*/
public class ReadWriteMonitor
{
/**
* <0 : writing (cannot go beyond -1, i.e one concurrent writer) =0 : idle >0 : reading (number of concurrent
* readers)
*/
private int status = 0;
/**
* Concurrent reading is allowed Blocking only when already writing.
*/
public synchronized void enterRead()
{
while (status < 0)
{
try
{
wait();
}
catch (InterruptedException e)
{
// ignore
}
}
status++;
}
/**
* Only one writer at a time is allowed to perform Blocking only when already writing or reading.
*/
public synchronized void enterWrite()
{
while (status != 0)
{
try
{
wait();
}
catch (InterruptedException e)
{
// ignore
}
}
status--;
}
/**
* Only notify waiting writer(s) if last reader
*/
public synchronized void exitRead()
{
if (--status == 0)
notifyAll();
}
/**
* When writing is over, all readers and possible writers are granted permission to restart concurrently
*/
public synchronized void exitWrite()
{
if (++status == 0)
notifyAll();
}
/**
* Atomic exitRead/enterWrite: Allows to keep monitor in between exit read and next enter write. Use when writing
* changes is optional, otherwise call the individual methods. Returns false if multiple readers are accessing the
* index.
*/
public synchronized boolean exitReadEnterWrite()
{
if (status != 1)
return false; // only continue if this is the only reader
status = -1;
return true;
}
/**
* Atomic exitWrite/enterRead: Allows to keep monitor in between exit write and next enter read. When writing is
* over, all readers are granted permissing to restart concurrently. This is the same as:
*
* <pre>
* synchronized (monitor)
* {
* monitor.exitWrite();
* monitor.enterRead();
* }
* </pre>
*/
public synchronized void exitWriteEnterRead()
{
this.exitWrite();
this.enterRead();
}
public String toString()
{
StringBuffer buffer = new StringBuffer();
if (status == 0)
{
buffer.append("Monitor idle "); //$NON-NLS-1$
}
else if (status < 0)
{
buffer.append("Monitor writing "); //$NON-NLS-1$
}
else if (status > 0)
{
buffer.append("Monitor reading "); //$NON-NLS-1$
}
buffer.append("(status = "); //$NON-NLS-1$
buffer.append(this.status);
buffer.append(")"); //$NON-NLS-1$
return buffer.toString();
}
}