path: root/java/awt/EventQueue.java

/* Copyright (C) 1999, 2000, 2001, 2002, 2003  Free Software Foundation

This file is part of GNU Classpath.

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package java.awt;

import java.awt.event.ActionEvent;
import java.awt.event.InputEvent;
import java.awt.event.InvocationEvent;
import java.awt.event.WindowEvent;
import java.lang.reflect.InvocationTargetException;
import java.util.EmptyStackException;

import gnu.java.awt.ClasspathToolkit;

/* 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.
 */

/**
 * 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 AWTEvent currentEvent;
  private long lastWhen = System.currentTimeMillis();

  private EventDispatchThread dispatchThread = new EventDispatchThread(this);
  private boolean shutdown = false;

  synchronized void setShutdown (boolean b) 
  {
    shutdown = b;
  }

  synchronized boolean isShutdown ()
  {
    if (shutdown)
      return true;

    // This is the exact self-shutdown condition specified in J2SE:
    // http://java.sun.com/j2se/1.4.2/docs/api/java/awt/doc-files/AWTThreadIssues.html
    
    if (peekEvent() == null
        && ((ClasspathToolkit) Toolkit.getDefaultToolkit()).nativeQueueEmpty())
      {
        Frame[] frames = Frame.getFrames();
        for (int i = 0; i < frames.length; ++i)
          if (frames[i].isDisplayable())
            return false;
        return true;
      }
    return false;
  }

  /**
   * 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)
      {
        // Only the EventDispatchThread associated with the top of the stack is
        // allowed to get events from the native source; everyone else just
        // waits on the head of the queue.

        if (isDispatchThread())
          {
            // We are not allowed to return null from this method, yet it
            // is possible that we actually have run out of native events
            // in the enclosing while() loop, and none of the native events
            // happened to cause AWT events. We therefore ought to check
            // the isShutdown() condition here, before risking a "native
            // wait". If we check it before entering this function we may
            // wait forever for events after the shutdown condition has
            // arisen.

            if (isShutdown())
              throw new InterruptedException();

            ((ClasspathToolkit) Toolkit.getDefaultToolkit()).iterateNativeQueue(this);
          }
        else
          {
            try
              {
                wait();
              }
            catch (InterruptedException ie)
              {
              }
          }
      }

    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 evt The event to post to the queue.
   *
   * @exception NullPointerException If event is null.
   */
  public synchronized void postEvent(AWTEvent evt)
  {
    if (evt == null)
      throw new NullPointerException();

    if (next != null)
      {
        next.postEvent(evt);
        return;
      }

    /* 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;
      }
    
    if (dispatchThread == null || !dispatchThread.isAlive())
      {
        dispatchThread = new EventDispatchThread(this);
        dispatchThread.start();
      }

    // Window events might represent the closing of a window, which
    // might cause the end of the dispatch thread's life, so we'll wake
    // it up here to give it a chance to check for shutdown.

    if (!isDispatchThread() 
        || (evt.getID() == WindowEvent.WINDOW_CLOSED)
        || (evt.getID() == WindowEvent.WINDOW_CLOSING))
      ((ClasspathToolkit) Toolkit.getDefaultToolkit()).wakeNativeQueue();

    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
  {
    if (isDispatchThread ())
      throw new Error("Can't call invokeAndWait from event dispatch thread");

    EventQueue eq = Toolkit.getDefaultToolkit().getSystemEventQueue(); 
    Thread current = Thread.currentThread();

    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);
  }

  /**
   * This arranges for runnable to have its run method called in the
   * dispatch thread of the EventQueue.  This will happen after all
   * pending events are processed.
   *
   * @since 1.2
   */
  public static void invokeLater(Runnable runnable)
  {
    EventQueue eq = Toolkit.getDefaultToolkit().getSystemEventQueue(); 

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

    eq.postEvent(ie);
  }

  /**
   * Return true if the current thread is the current AWT event dispatch
   * thread.
   */
  public static boolean isDispatchThread()
  {
    EventQueue eq = Toolkit.getDefaultToolkit().getSystemEventQueue();
    
    /* Find last EventQueue in chain */ 
    while (eq.next != null)
      eq = eq.next;

    return (Thread.currentThread() == eq.dispatchThread);
  }

  /**
   * Return the event currently being dispatched by the event
   * dispatch thread.  If the current thread is not the event
   * dispatch thread, this method returns null.
   *
   * @since 1.4
   */
  public static AWTEvent getCurrentEvent()
  {
    EventQueue eq = Toolkit.getDefaultToolkit().getSystemEventQueue(); 
    Thread ct = Thread.currentThread();
    
    /* Find out if this thread is the dispatch thread for any of the
       EventQueues in the chain */ 
    while (ct != eq.dispatchThread)
      {
        // Try next EventQueue, if any
        if (eq.next == null)
           return null;  // Not an event dispatch thread
        eq = eq.next;
      }

    return eq.currentEvent;
  }

  /**
   * Allows a custom EventQueue implementation to replace this one. 
   * All pending events are transferred to the new queue. Calls to postEvent,
   * getNextEvent, and peekEvent and others 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)
  {
    if (newEventQueue == null)
      throw new NullPointerException ();

    /* Make sure we are at the top of the stack because callers can
       only get a reference to the one at the bottom using
       Toolkit.getDefaultToolkit().getSystemEventQueue() */
    if (next != null)
      {
        next.push (newEventQueue);
        return;
      }

    /* Make sure we have a live dispatch thread to drive the queue */
    if (dispatchThread == null)
      dispatchThread = new EventDispatchThread(this);

    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();

    /* The order is important here, we must get the prev lock first,
       or deadlock could occur as callers usually get here following
       prev's next pointer, and thus obtain prev's lock before trying
       to get this lock. */
    synchronized (prev)
      {
        prev.next = next;
        if (next != null)
          next.prev = prev;

        synchronized (this)
          {
            int i = next_out;
            while (i != next_in)
              {
                prev.postEvent(queue[i]);
                next_out = i;
                if (++i == queue.length)
                  i = 0;
              }
	    // Empty the queue so it can be reused
	    next_in = 0;
	    next_out = 0;

            ((ClasspathToolkit) Toolkit.getDefaultToolkit()).wakeNativeQueue();
            setShutdown(true);
	    dispatchThread = null;
            this.notifyAll();
          }
      }
  }

  /**
   * 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)
  {
    currentEvent = evt;

    if (evt instanceof InputEvent)
      lastWhen = ((InputEvent) evt).getWhen();
    else if (evt instanceof ActionEvent)
      lastWhen = ((ActionEvent) evt).getWhen();
    else if (evt instanceof InvocationEvent)
      lastWhen = ((InvocationEvent) evt).getWhen();

    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()
  {
    EventQueue eq = Toolkit.getDefaultToolkit().getSystemEventQueue(); 
    if (Thread.currentThread() != eq.dispatchThread)
      return System.currentTimeMillis();
    return eq.lastWhen;
  }
}