/* EventQueue.java -- Event queuing mechanism
   Copyright (C) 1999 Free Software Foundation, Inc.

This file is part of the non-peer AWT libraries of GNU Classpath.

This library is free software; you can redistribute it and/or modify
it under the terms of the GNU Library General Public License as published 
by the Free Software Foundation, either version 2 of the License, or
(at your option) any later verion.

This library 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.  See the
GNU Library General Public License for more details.

You should have received a copy of the GNU Library General Public License
along with this library; if not, write to the Free Software Foundation
Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307 USA. */


package java.awt;

/**
  * This class manages a queue of <code>AWTEvent</code> objects that
  * are posted to it.  The AWT system uses only one event queue for all
  * events.
  *
  * @author Aaron M. Renn (arenn@urbanophile.com)
  */
public class EventQueue
{

/*
 * Instance Methods
 */

// The queue.  We added a package protected field to AWTEvent to make it
// a convenient linked list.
private AWTEvent queue;

/*************************************************************************/

/*
 * Constructors
 */

/**
  * Initializes a new instance of <code>EventQueue</code>.
  */
public
EventQueue()
{
  EventDispatcher ed = new EventDispatcher(this);
  Thread t = new Thread(ed);
  t.start();
}

/*************************************************************************/

/*
 * Instance Variables
 */

/**
  * Posts a new event to the queue.
  *
  * @param event The event to post to the queue.
  */
public synchronized void
postEvent(AWTEvent event)
{
  if (queue == null)
    queue = event;
  else
    {
      AWTEvent end = queue;
      while (end.next != null)
        end = end.next;

      end.next = queue;
    }
  notify();
}

/*************************************************************************/

/**
  * Returns the next event in the queue.  This method will block until
  * an event is available or until the thread is interrupted.
  *
  * @return The next event in the queue.
  *
  * @exception InterruptedException If this thread is interrupted while
  * waiting for an event to be posted to the queue.
  */
public synchronized AWTEvent
getNextEvent() throws InterruptedException
{
  for (;;)
    {
      if (queue != null)
        {
          AWTEvent evt = queue;
          queue = queue.next;
          evt.next = null;
          return(evt);
        }
      wait();
    }
}
 
/*************************************************************************/

/**
  * Returns the next event in the queue without removing it from the queue.
  * This method will block until an event is available or until the thread
  * is interrupted.
  *
  * @return The next event in the queue.
  */
public synchronized AWTEvent
peekEvent()
{
  for (;;)
    {
      if (queue != null)
        {
          // We are taking a chance that the user doesn't repost the same
          // event back to the queue, but AWTEvent isn't cloneable so we
          // don't have much choice.  If this becomes a problem we'll have
          // to write a wrapper class for enqueuing.
          return(queue);
        }

      try
        {
          wait();
        }
      catch(InterruptedException e) {  }
    }
}

/*************************************************************************/

/**
  * Returns the next event in the queue that has the specified id
  * without removing it from the queue.
  * This method will block until an event is available or until the thread
  * is interrupted.
  *
  * @param id The event id to return.
  *
  * @return The next event in the queue.
  */
public synchronized AWTEvent
peekEvent(int id)
{
  for(;;)
    {
      if (queue != null)
        {
          AWTEvent evt = queue;
          while (evt != null)
            {
              if (evt.getID() == id)
                 return(evt);
              evt = evt.next;
            }
        }

      try
        {
          wait();
        }
      catch(InterruptedException e) {  }
    }
}

} // class EventQueue