gcc/libjava/java/awt/EventQueue.java

/* Copyright (C) 1999, 2000, 2001, 2002  Free Software Foundation

This file is part of GNU Classpath.

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

GNU Classpath 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
General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Classpath; see the file COPYING.  If not, write to the
Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA.

As a special exception, if you link this library with other files to
produce an executable, this library does not by itself cause the
resulting executable to be covered by the GNU General Public License.
This exception does not however invalidate any other reasons why the
executable file might be covered by the GNU General Public License. */


package java.awt;

import java.awt.event.*;
import java.util.EmptyStackException;
import java.lang.reflect.InvocationTargetException;

/* Written using on-line Java 2 Platform Standard Edition v1.3 API 
 * Specification, as well as "The Java Class Libraries", 2nd edition 
 * (Addison-Wesley, 1998).
 * Status:  Believed complete, but untested. Check FIXME's.
 */

/**
 * 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 Bryce McKinlay
 * @author Aaron M. Renn (arenn@urbanophile.com)
 */
public class EventQueue
{
  private static final int INITIAL_QUEUE_DEPTH = 8;
  private AWTEvent[] queue = new AWTEvent[INITIAL_QUEUE_DEPTH];

  private int next_in = 0; // Index where next event will be added to queue
  private int next_out = 0; // Index of next event to be removed from queue

  private EventQueue next;
  private EventQueue prev;

  private EventDispatchThread dispatchThread = new EventDispatchThread(this);

  /**
   * Initializes a new instance of <code>EventQueue</code>.
   */
  public EventQueue()
  {
  }

  /**
   * 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
  {
    if (next != null)
      return next.getNextEvent();

    while (next_in == next_out)
      wait();

    AWTEvent res = queue[next_out];

    if (++next_out == queue.length)
      next_out = 0;
    return res;
  }

  /**
   * 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.
   * @specnote Does not block. Returns null if there are no events on the 
   *            queue. 
   */ 
  public synchronized AWTEvent peekEvent()
  {
    if (next != null)
      return next.peekEvent();

    if (next_in != next_out)
      return queue[next_out];
    else return null;
  }

  /**
   * 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.
   *
   * @specnote Does not block. Returns null if there are no matching events 
   *            on the queue. 
   */ 
  public synchronized AWTEvent peekEvent(int id)
  {
    if (next != null)
      return next.peekEvent(id);

    int i = next_out;
    while (i != next_in)
      {
        AWTEvent qevt = queue[i];
        if (qevt.id == id)
	  return qevt;
      }
    return null;
  }

  /**
   * Posts a new event to the queue.
   *
   * @param event The event to post to the queue.
   */
  public synchronized void postEvent(AWTEvent evt)
  {
    if (next != null)
      {
        next.postEvent(evt);
	return;
      }
    // FIXME: Security checks?

    /* Check for any events already on the queue with the same source 
       and ID. */	
    int i = next_out;
    while (i != next_in)
      {
        AWTEvent qevt = queue[i];
	Object src;
	if (qevt.id == evt.id
	    && (src = qevt.getSource()) == evt.getSource()
	    && src instanceof Component)
	  {
	    /* If there are, call coalesceEvents on the source component 
	       to see if they can be combined. */
	    Component srccmp = (Component) src;
	    AWTEvent coalesced_evt = srccmp.coalesceEvents(qevt, evt);
	    if (coalesced_evt != null)
	      {
	        /* Yes. Replace the existing event with the combined event. */
	        queue[i] = coalesced_evt;
		return;
	      }
            break;
	  }
	if (++i == queue.length)
	  i = 0;
      }

    queue[next_in] = evt;    
    if (++next_in == queue.length)
      next_in = 0;

    if (next_in == next_out)
      {
        /* Queue is full. Extend it. */
        AWTEvent[] oldQueue = queue;
	queue = new AWTEvent[queue.length * 2];

	int len = oldQueue.length - next_out;
	System.arraycopy(oldQueue, next_out, queue, 0, len);
	if (next_out != 0)
	  System.arraycopy(oldQueue, 0, queue, len, next_out);

	next_out = 0;
	next_in = oldQueue.length;
      }
    notify();
  }

  /** @since JDK1.2 */
  public static void invokeAndWait(Runnable runnable)
    throws InterruptedException, InvocationTargetException
  {
    EventQueue eq = Toolkit.getDefaultToolkit().getSystemEventQueue(); 
    Thread current = Thread.currentThread();
    if (current == eq.dispatchThread)
      throw new Error("Can't call invokeAndWait from event dispatch thread");

    InvocationEvent ie = 
      new InvocationEvent(eq, runnable, current, true);

    synchronized (current)
      {
	eq.postEvent(ie);
	current.wait();
      }

    Exception exception;

    if ((exception = ie.getException()) != null)
      throw new InvocationTargetException(exception);
  }

  /** @since JDK1.2 */
  public static void invokeLater(Runnable runnable)
  {
    EventQueue eq = Toolkit.getDefaultToolkit().getSystemEventQueue(); 

    InvocationEvent ie = 
      new InvocationEvent(eq, runnable, null, false);

    eq.postEvent(ie);
  }

  public static boolean isDispatchThread()
  {
    EventQueue eq = Toolkit.getDefaultToolkit().getSystemEventQueue(); 
    return (Thread.currentThread() == eq.dispatchThread);
  }

  /** Allows a custom EventQueue implementation to replace this one. 
    * All pending events are transferred to the new queue. Calls to postEvent,
    * getNextEvent, and peekEvent are forwarded to the pushed queue until it
    * is removed with a pop().
    */
  public synchronized void push(EventQueue newEventQueue)
  {
    int i = next_out;
    while (i != next_in)
      {
        newEventQueue.postEvent(queue[i]);
	next_out = i;
	if (++i == queue.length)
	  i = 0;
      }

    next = newEventQueue;
    newEventQueue.prev = this;    
  }

  /** Transfer any pending events from this queue back to the parent queue that
    * was previously push()ed. Event dispatch from this queue is suspended. */
  protected void pop() throws EmptyStackException
  {
    if (prev == null)
      throw new EmptyStackException();

    // Don't synchronize both this and prev at the same time, or deadlock could
    // occur.
    synchronized (prev)
      {
	prev.next = null;
      }

    synchronized (this)
      {
	int i = next_out;
	while (i != next_in)
	  {
            prev.postEvent(queue[i]);
	    next_out = i;
	    if (++i == queue.length)
	      i = 0;
	  }
      }
  }

  protected void dispatchEvent(AWTEvent evt)
  {
    if (evt instanceof ActiveEvent)
      {
        ActiveEvent active_evt = (ActiveEvent) evt;
	active_evt.dispatch();
      }
    else
      {
	Object source = evt.getSource();

	if (source instanceof Component)
	  {
            Component srccmp = (Component) source;
	    srccmp.dispatchEvent(evt);
	  }
	else if (source instanceof MenuComponent)
	  {
	    MenuComponent srccmp = (MenuComponent) source;
	    srccmp.dispatchEvent(evt);
	  }
      }
  }
}