001/*
002 * HA-JDBC: High-Availability JDBC
003 * Copyright (c) 2004-2007 Paul Ferraro
004 * 
005 * This library is free software; you can redistribute it and/or modify it 
006 * under the terms of the GNU Lesser General Public License as published by the 
007 * Free Software Foundation; either version 2.1 of the License, or (at your 
008 * option) any later version.
009 * 
010 * This library is distributed in the hope that it will be useful, but WITHOUT
011 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 
012 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License 
013 * for more details.
014 * 
015 * You should have received a copy of the GNU Lesser General Public License
016 * along with this library; if not, write to the Free Software Foundation, 
017 * Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
018 * 
019 * Contact: ferraro@users.sourceforge.net
020 */
021package net.sf.hajdbc.util.concurrent;
022
023import java.util.concurrent.Semaphore;
024import java.util.concurrent.TimeUnit;
025import java.util.concurrent.locks.Condition;
026import java.util.concurrent.locks.Lock;
027
028/**
029 * An implementation of {@link java.util.concurrent.locks.Lock} using a binary semaphore.
030 * Unlike the {@link java.util.concurrent.locks.ReentrantLock} this lock can be locked and unlocked by different threads.
031 * Conditions are not supported.
032 * 
033 * @author Paul Ferraro
034 */
035public class SemaphoreLock implements Lock
036{
037        private final Semaphore semaphore;
038        
039        public SemaphoreLock(boolean fair)
040        {
041                this(new Semaphore(1, fair));
042        }
043        
044        SemaphoreLock(Semaphore semaphore)
045        {
046                this.semaphore = semaphore;
047        }
048        
049        /**
050         * @see java.util.concurrent.locks.Lock#lock()
051         */
052        @Override
053        public void lock()
054        {
055                this.semaphore.acquireUninterruptibly();
056        }
057
058        /**
059         * @see java.util.concurrent.locks.Lock#lockInterruptibly()
060         */
061        @Override
062        public void lockInterruptibly() throws InterruptedException
063        {
064                this.semaphore.acquire();
065        }
066
067        /**
068         * @see java.util.concurrent.locks.Lock#newCondition()
069         */
070        @Override
071        public Condition newCondition()
072        {
073                throw new UnsupportedOperationException();
074        }
075
076        /**
077         * @see java.util.concurrent.locks.Lock#tryLock()
078         */
079        @Override
080        public boolean tryLock()
081        {
082                return this.semaphore.tryAcquire();
083        }
084
085        /**
086         * @see java.util.concurrent.locks.Lock#tryLock(long, java.util.concurrent.TimeUnit)
087         */
088        @Override
089        public boolean tryLock(long time, TimeUnit unit) throws InterruptedException
090        {
091                return this.semaphore.tryAcquire(time, unit);
092        }
093
094        /**
095         * @see java.util.concurrent.locks.Lock#unlock()
096         */
097        @Override
098        public void unlock()
099        {
100                this.semaphore.release();
101        }
102}