com.mchange.v2.lock.SimpleSharedUseExclusiveUseLock Maven / Gradle / Ivy
/*
* Distributed as part of mchange-commons-java 0.2.9
*
* Copyright (C) 2015 Machinery For Change, Inc.
*
* Author: Steve Waldman
*
* This library is free software; you can redistribute it and/or modify
* it under the terms of EITHER:
*
* 1) The GNU Lesser General Public License (LGPL), version 2.1, as
* published by the Free Software Foundation
*
* OR
*
* 2) The Eclipse Public License (EPL), version 1.0
*
* You may choose which license to accept if you wish to redistribute
* or modify this work. You may offer derivatives of this work
* under the license you have chosen, or you may provide the same
* choice of license which you have been offered here.
*
* This software is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
*
* You should have received copies of both LGPL v2.1 and EPL v1.0
* along with this software; see the files LICENSE-EPL and LICENSE-LGPL.
* If not, the text of these licenses are currently available at
*
* LGPL v2.1: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html
* EPL v1.0: http://www.eclipse.org/org/documents/epl-v10.php
*
*/
package com.mchange.v2.lock;
/**
* NONREENTRANT!!!
* also... would be more efficient if we
* segregated readers and writers into
* separate wait sets.
*/
public class SimpleSharedUseExclusiveUseLock implements SharedUseExclusiveUseLock
{
private int waiting_readers = 0;
private int active_readers = 0;
private int waiting_writers = 0;
private boolean writer_active = false;
public synchronized void acquireShared() throws InterruptedException
{
try
{
++waiting_readers;
while (! okayToRead())
this.wait();
++active_readers;
}
finally
{
--waiting_readers;
}
}
public synchronized void relinquishShared()
{
--active_readers;
this.notifyAll();
}
public synchronized void acquireExclusive() throws InterruptedException
{
try
{
++waiting_writers;
while (! okayToWrite())
this.wait();
writer_active = true;
}
finally
{
--waiting_writers;
}
}
public synchronized void relinquishExclusive()
{
writer_active = false;
this.notifyAll();
}
private boolean okayToRead()
{ return (!writer_active && waiting_writers == 0); }
private boolean okayToWrite()
{ return (active_readers == 0 && !writer_active); }
}