/*
* The Apache Software License, Version 1.1
*
*
* Copyright (c) 2003 The Apache Software Foundation.  All rights 
* reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
*    notice, this list of conditions and the following disclaimer. 
*
* 2. Redistributions in binary form must reproduce the above copyright
*    notice, this list of conditions and the following disclaimer in
*    the documentation and/or other materials provided with the
*    distribution.
*
* 3. The end-user documentation included with the redistribution,
*    if any, must include the following acknowledgment:  
*       "This product includes software developed by the
*        Apache Software Foundation (http://www.apache.org/)."
*    Alternately, this acknowledgment may appear in the software itself,
*    if and wherever such third-party acknowledgments normally appear.
*
* 4. The names "Apache" and "Apache Software Foundation" must 
*    not be used to endorse or promote products derived from this
*    software without prior written permission. For written 
*    permission, please contact apache@apache.org.
*
* 5. Products derived from this software may not be called "Apache 
*    XMLBeans", nor may "Apache" appear in their name, without prior 
*    written permission of the Apache Software Foundation.
*
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
* ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
* ====================================================================
*
* This software consists of voluntary contributions made by many
* individuals on behalf of the Apache Software Foundation and was
* originally based on software copyright (c) 2000-2003 BEA Systems 
* Inc., <http://www.bea.com/>. For more information on the Apache Software
* Foundation, please see <http://www.apache.org/>.
*/

package org.apache.xmlbeans.impl.common;

public class Mutex
{
    private Thread  owner      = null;  // Owner of mutex, null if nobody
    private int     lock_count = 0;

    /**
     * Acquire the mutex. The mutex can be acquired multiple times
     * by the same thread, provided that it is released as many
     * times as it is acquired. The calling thread blocks until
     * it has acquired the mutex. (There is no timeout).
     */
    public synchronized void acquire() throws InterruptedException
    {
        while (tryToAcquire() == false)
        {
            this.wait();
        }
    }

    /**
     * Attempts to acquire the mutex. Returns false (and does not
     * block) if it can't get it.
     */

    public synchronized boolean tryToAcquire()
    {
        // Try to get the mutex. Return true if you got it.

        if( owner == null )
        {
            owner = Thread.currentThread();
            lock_count = 1;
            return true;
        }

        if( owner == Thread.currentThread() )
        {
            ++lock_count;
            return true;
        }

        return false;
    }

    /**
     * Release the mutex. The mutex has to be released as many times
     * as it was acquired to actually unlock the resource. The mutex
     * must be released by the thread that acquired it
     *
     * @throws IllegalStateException (a RuntimeException) if a thread
     *      other than the current owner tries to release the mutex.
     */

    public synchronized void release()
    {
        if (owner != Thread.currentThread())
            throw new IllegalStateException("Thread calling release() doesn't own mutex");

        if (--lock_count <= 0)
        {
            owner = null;
            notify();
        }
    }
}