path: root/libjava/java/awt/EventQueue.java

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

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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.
   *
   * @exception NullPointerException If event is null.
   */
  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();
  }

  /**
   * Causes runnable to have its run method called in the dispatch thread of the
   * EventQueue. This will happen after all pending events are processed. The
   * call blocks until this has happened. This method will throw an Error if
   * called from the event dispatcher thread.
   *
   * @exception InterruptedException If another thread has interrupted
   * this thread.
   * @exception InvocationTargetException If an exception is thrown when running
   * runnable.
   *
   * @since 1.2
   */
  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().
    *
    * @exception NullPointerException if newEventQueue is null.
    */
  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.
    *
    * @exception EmptyStackException If no previous push was made on this
    * EventQueue.
    */
  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;
	  }
      }
  }

  /**
   * Dispatches an event. The manner in which the event is dispatched depends
   * upon the type of the event and the type of the event's source object.
   *
   * @exception NullPointerException If event is null.
   */
  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);
	  }
      }
  }

  /**
   * Returns the timestamp of the most recent event that had a timestamp, or
   * the initialization time of the event queue if no events have been fired.
   * At present, only <code>InputEvent</code>s, <code>ActionEvent</code>s,
   * <code>InputMethodEvent</code>s, and <code>InvocationEvent</code>s have
   * timestamps, but this may be added to other events in future versions.
   * If this is called by the event dispatching thread, it can be any
   * (sequential) value, but to other threads, the safest bet is to return
   * System.currentTimeMillis().
   *
   * @return the most recent timestamp
   * @see InputEvent#getWhen()
   * @see ActionEvent#getWhen()
   * @see InvocationEvent#getWhen()
   * @see InputMethodEvent#getWhen()
   * @since 1.4
   */
  public static long getMostRecentEventTime()
  {
    // XXX For now, this ONLY does the current time.
    return System.currentTimeMillis();
  }
} // class EventQueue