/*******************************************************************************
* Copyright © 2000, 2013 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 org.eclipse.edt.ide.core.internal.model.indexing;
/**
* Monitor ensuring no more than one writer working concurrently.
* Multiple readers are allowed to perform simultaneously.
*/
public class EGLReadWriteMonitor {
/**
* <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){
}
}
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){
}
}
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 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();
}
}