/*
 * Copyright (c) 2003, KNOPFLERFISH project
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following
 * conditions are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 *
 * - 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.
 *
 * - Neither the name of the KNOPFLERFISH project nor the names of its
 *   contributors may be used to endorse or promote products derived
 *   from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS 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
 * COPYRIGHT OWNER OR 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.
 */

package org.knopflerfish.util;

/**
 ** The <code>Semaphore</code> class handles synchronization and waiting for values.
 ** @author Johan Agat and Anders Rimen
 */
public class Semaphore  
{
  private Object value = null;
  private boolean closed = false;

  /**
   *	Waits up to <code>timeout</code> milliseconds for this
   *	Semaphore to receive a value.
   *
   * 	@return The value of the Semaphore or null if this Semaphore
   * 	has been closed or if the specified timeout has expired.
   **/
  public synchronized Object get(long timeout) {
    long until = System.currentTimeMillis() + timeout;
    while ( !closed && value == null ) {
      try {
	long t = until - System.currentTimeMillis();
	if ( t >= 0 )
	  wait(t);
	else
	  return null;
      }
      catch (InterruptedException ignore){}
    }
    return value;
  }


  /**
   *	Sets the value of this Semaphore.  This will cause all blocked
   *	calls to get() to return the value.  If set() is called
   *	several times with a short or no delay between the calls, the
   *	exact value returned by a given blocked call to get() is not
   *	deterministic.
   *
   **/
  public synchronized void set(Object v) {
    if ( closed ) 
      return;
    value = v;
//    setCount++;
    notifyAll();
  }


  public synchronized void reset() {
    value = null;
  }

  public synchronized void close() {
    value = null;
    closed = true;
    notifyAll();
  }

}