AsyncInitSupport.java

/*
 *                 Sun Public License Notice
 * 
 * The contents of this file are subject to the Sun Public License
 * Version 1.0 (the "License"). You may not use this file except in
 * compliance with the License. A copy of the License is available at
 * http://www.sun.com/
 * 
 * The Original Code is NetBeans. The Initial Developer of the Original
 * Code is Sun Microsystems, Inc. Portions Copyright 1997-2003 Sun
 * Microsystems, Inc. All Rights Reserved.
 */

package org.openide.util;

import java.awt.AWTEvent;
import java.awt.Component;
import java.awt.Toolkit;
import java.awt.event.AWTEventListener;
import java.awt.event.HierarchyEvent;
import java.awt.event.HierarchyListener;
import javax.swing.SwingUtilities;

/** Performance helper class, allows to run post-init task for given component.
 * Can also handle cancel logic if contained in AsyncGUIJob.
 * Class is designed for one time use, can't be used to perform async init
 * more then once.
 * Restrictions: Note that for correct functionality given component must not
 * be showing at construction time of this class, however shouldn't stay hidden
 * forever as memory leak may occur.
 *
 * @author Dafe Simonek
 */
final class AsyncInitSupport implements AWTEventListener,
                                         HierarchyListener,
                                         Runnable {
    /** lock for access to wasCancelled flag */
    private static final Object CANCELLED_LOCK = new Object();
    /** task in which post init code from AsyncJob is executed */
    private Task initTask;
    /** true after cancel request came, false otherwise */
    private boolean wasCancelled;
    /** Component requesting asynchronous initialization */ 
    private Component comp4Init;
    /** Job that performs async init task */
    private AsyncGUIJob initJob;
    
    /** Creates a new instance of AsyncInitComponent
     * @param comp4Init Component to be initialized. Mustn't be showing at this
     * time. IllegalStateException is thrown if component is already showing.
     * @param initJob Instance of initialization job.
     */
    public AsyncInitSupport(Component comp4Init, AsyncGUIJob initJob) {
        this.comp4Init = comp4Init;
        this.initJob = initJob;
        if (comp4Init.isShowing()) {
            throw new IllegalStateException(
                "Component already shown, can't be inited: " + comp4Init
            );
        }
        Toolkit.getDefaultToolkit().addAWTEventListener(this, AWTEvent.PAINT_EVENT_MASK);
        comp4Init.addHierarchyListener(this);
    }
    
    /** Invokes execution of init code in non-ED thread.
     * @param evt ignored
     */
    public void eventDispatched (AWTEvent event) {
        if ((event.getSource() instanceof Component) &&
            SwingUtilities.isDescendingFrom(comp4Init, (Component)(event.getSource()))) {
            Toolkit.getDefaultToolkit().removeAWTEventListener(this);
            initTask = RequestProcessor.getDefault().post(this);
        }
    }

    /** Stops listening to asociated component it isn't showing anymore,
     * calls cancel if desirable.
     * @param evt hierarchy event
     */
    public void hierarchyChanged(HierarchyEvent evt) {
        if (((evt.getChangeFlags() & HierarchyEvent.SHOWING_CHANGED) != 0) &&
            !comp4Init.isShowing()) {
            comp4Init.removeHierarchyListener(this);
            cancel();
        }
    }
    
    /** Body of task executed in RequestProcessor. Runs AsyncGUIJob's worker
     * method and after its completion posts AsyncJob's UI update method
     * to AWT thread.
     */
    public void run() {
        if (!SwingUtilities.isEventDispatchThread()) {
            // first pass, executed in some of RP threads
            initJob.construct();
            comp4Init.removeHierarchyListener(this);
            // continue to invoke finished method only if hasn't been cancelled 
            boolean localCancel;
            synchronized (CANCELLED_LOCK) {
                localCancel = wasCancelled;
            }
            if (!localCancel) {
                SwingUtilities.invokeLater(this);
            }
        } else {
            // second pass, executed in event dispatch thread
            initJob.finished();
        }
    }

    /** Delegates valid cancel requests to asociated AsyncGUIJob, in the case
     * job supports cancelling. */
    private void cancel () {
        if ((initTask != null) && !initTask.isFinished() && 
            (initJob instanceof Cancellable)) {
            synchronized (CANCELLED_LOCK) {
                wasCancelled = true;
            }
            ((Cancellable)initJob).cancel();
        }
    }
    
    
}