appcontext.java

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/*
 * @(#)AppContext.java	1.35 06/10/10
 *
 * Copyright  1990-2008 Sun Microsystems, Inc. All Rights Reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER
 * 
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License version
 * 2 only, as published by the Free Software Foundation. 
 * 
 * This program 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 version 2 for more details (a copy is
 * included at /legal/license.txt). 
 * 
 * You should have received a copy of the GNU General Public License
 * version 2 along with this work; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
 * 02110-1301 USA 
 * 
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa
 * Clara, CA 95054 or visit www.sun.com if you need additional
 * information or have any questions. 
 */

package sun.awt;

import java.awt.AWTEvent;
import java.awt.EventQueue;
import java.awt.Frame;
import java.awt.Toolkit;
import java.awt.event.InvocationEvent;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.HashMap;
import java.util.IdentityHashMap;
import java.util.Enumeration;

import java.beans.PropertyChangeSupport;
import java.beans.PropertyChangeListener;

/**
 * The AppContext is a table referenced by ThreadGroup which stores
 * application service instances.  (If you are not writing an application
 * service, or don't know what one is, please do not use this class.)
 * The AppContext allows applet access to what would otherwise be
 * potentially dangerous services, such as the ability to peek at
 * EventQueues or change the look-and-feel of a Swing application.<p>
 *
 * Most application services use a singleton object to provide their
 * services, either as a default (such as getSystemEventQueue or 
 * getDefaultToolkit) or as static methods with class data (System).
 * The AppContext works with the former method by extending the concept
 * of "default" to be ThreadGroup-specific.  Application services
 * lookup their singleton in the AppContext.<p>
 *
 * For example, here we have a Foo service, with its pre-AppContext
 * code:<p>
 * <code><pre>
 *    public class Foo {
 *        private static Foo defaultFoo = new Foo();
 *
 *        public static Foo getDefaultFoo() {
 *            return defaultFoo;
 *        }
 *
 *    ... Foo service methods
 *    }</pre></code><p>
 *
 * The problem with the above is that the Foo service is global in scope,
 * so that applets and other untrusted code can execute methods on the
 * single, shared Foo instance.  The Foo service therefore either needs
 * to block its use by untrusted code using a SecurityManager test, or
 * restrict its capabilities so that it doesn't matter if untrusted code
 * executes it.<p>
 *
 * Here's the Foo class written to use the AppContext:<p>
 * <code><pre>
 *    public class Foo {
 *        public static Foo getDefaultFoo() {
 *            Foo foo = (Foo)AppContext.getAppContext().get(Foo.class);
 *            if (foo == null) {
 *                foo = new Foo();
 *                getAppContext().put(Foo.class, foo);
 *            }
 *            return foo;
 *        }
 *
 *    ... Foo service methods
 *    }</pre></code><p>
 *
 * Since a separate AppContext can exist for each ThreadGroup, trusted
 * and untrusted code have access to different Foo instances.  This allows
 * untrusted code access to "system-wide" services -- the service remains
 * within the AppContext "sandbox".  For example, say a malicious applet 
 * wants to peek all of the key events on the EventQueue to listen for
 * passwords; if separate EventQueues are used for each ThreadGroup
 * using AppContexts, the only key events that applet will be able to
 * listen to are its own.  A more reasonable applet request would be to
 * change the Swing default look-and-feel; with that default stored in
 * an AppContext, the applet's look-and-feel will change without 
 * disrupting other applets or potentially the browser itself.<p>
 *
 * Because the AppContext is a facility for safely extending application
 * service support to applets, none of its methods may be blocked by a
 * a SecurityManager check in a valid Java implementation.  Applets may
 * therefore safely invoke any of its methods without worry of being 
 * blocked.
 *
 * Note: If a SecurityManager is installed which derives from
 * sun.awt.AWTSecurityManager, it may override the
 * AWTSecurityManager.getAppContext() method to return the proper
 * AppContext based on the execution context, in the case where
 * the default ThreadGroup-based AppContext indexing would return
 * the main "system" AppContext.  For example, in an applet situation,
 * if a system thread calls into an applet, rather than returning the
 * main "system" AppContext (the one corresponding to the system thread),
 * an installed AWTSecurityManager may return the applet's AppContext
 * based on the execution context.
 *
 * @author  Thomas Ball
 * @author  Fred Ecks
 * @version 1.35 10/10/06
 */
public final class AppContext {

    /* Since the contents of an AppContext are unique to each Java 
     * session, this class should never be serialized. */

    /* The key to put()/get() the Java EventQueue into/from the AppContext.
     */
    public static final Object EVENT_QUEUE_KEY = new StringBuffer("EventQueue");

    /* A map of AppContexts, referenced by ThreadGroup.
     */
    private static IdentityHashMap threadGroup2appContext = null;

    /* The main "system" AppContext, used by everything not otherwise
       contained in another AppContext.
     */
    private static AppContext mainAppContext = null;

    /*
     * The hash map associated with this AppContext.  A private delegate
     * is used instead of subclassing HashMap so as to avoid all of
     * HashMap's potentially risky methods, such as clear(), elements(),
     * putAll(), etc.
     */
    private final HashMap table = new HashMap();

    private final ThreadGroup threadGroup;

    /**
     * If any <code>PropertyChangeListeners</code> have been registered,
     * the <code>changeSupport</code> field describes them.
     *
     * @see #addPropertyChangeListener
     * @see #removePropertyChangeListener
     * @see #firePropertyChange
     *
     * private PropertyChangeSupport changeSupport = null;
     */

    public static final String DISPOSED_PROPERTY_NAME = "disposed";

    private boolean isDisposed = false; // true if AppContext is disposed

    public boolean isDisposed() {
        return isDisposed;
    }


    static {
        // On the main Thread, we get the ThreadGroup, make a corresponding
        // AppContext, and instantiate the Java EventQueue.  This way, legacy
        // code is unaffected by the move to multiple AppContext ability.
        AccessController.doPrivileged(new PrivilegedAction() {
          public Object run() {
            ThreadGroup currentThreadGroup =
                                Thread.currentThread().getThreadGroup();
            ThreadGroup parentThreadGroup = currentThreadGroup.getParent();
            while (parentThreadGroup != null) {
                // Find the root ThreadGroup to construct our main AppContext
                currentThreadGroup = parentThreadGroup;
                parentThreadGroup = currentThreadGroup.getParent();
            }
            mainAppContext = new AppContext(currentThreadGroup);
            numAppContexts = 1;
            return mainAppContext;
          }
        });
    }

    /*
     * The total number of AppContexts, system-wide.  This number is
     * incremented at the beginning of the constructor, and decremented
     * at the end of dispose().  getAppContext() checks to see if this
     * number is 1.  If so, it returns the sole AppContext without
     * checking Thread.currentThread().
     */
    private static int numAppContexts;

    /*
     * The context ClassLoader that was used to create this AppContext.
     */
    private final ClassLoader contextClassLoader;

    /**
     * Constructor for AppContext.  This method is <i>not</i> public,
     * nor should it ever be used as such.  The proper way to construct
     * an AppContext is through the use of SunToolkit.createNewAppContext.
     * A ThreadGroup is created for the new AppContext, a Thread is
     * created within that ThreadGroup, and that Thread calls
     * SunToolkit.createNewAppContext before calling anything else.
     * That creates both the new AppContext and its EventQueue.
     * 
     * @param   threadGroup     The ThreadGroup for the new AppContext
     * @see     sun.awt.SunToolkit
     * @since   JDK1.2
     */
    AppContext(ThreadGroup threadGroup) {
        numAppContexts++;

        if (threadGroup2appContext == null) {
            threadGroup2appContext = new IdentityHashMap();
        }
        this.threadGroup = threadGroup;
        threadGroup2appContext.put(threadGroup, this);

        this.contextClassLoader = 
            (ClassLoader) AccessController.doPrivileged(new PrivilegedAction() {
                    public Object run() {
                        return Thread.currentThread().getContextClassLoader();
                    }
                });
    }

    private static MostRecentThreadAppContext mostRecentThreadAppContext = null;

    /**
     * Returns the appropriate AppContext for the caller, 
     * as determined by its ThreadGroup.  If the main "system" AppContext
     * would be returned and there's an AWTSecurityManager installed, it
     * is called to get the proper AppContext based on the execution
     * context.
     *
     * @return  the AppContext for the caller.
     * @see     java.lang.ThreadGroup
     * @since   JDK1.2
     */
    public final static AppContext getAppContext() {
        if (numAppContexts == 1)   // If there's only one system-wide,
            return mainAppContext; // return the main system AppContext.

        final Thread currentThread = Thread.currentThread();

        AppContext appContext = null;

        // Note: this most recent Thread/AppContext caching is thread-hot.
        // A simple test using SwingSet found that 96.8% of lookups
        // were matched using the most recent Thread/AppContext.  By
        // instantiating a simple MostRecentThreadAppContext object on
        // cache misses, the cache hits can be processed without
        // synchronization.

        MostRecentThreadAppContext recent = mostRecentThreadAppContext;
        if ((recent != null) && (recent.thread == currentThread))  {
            appContext = recent.appContext; // Cache hit
        } else {
          appContext = (AppContext)AccessController.doPrivileged(
                                            new PrivilegedAction() {
            public Object run() {
            // Get the current ThreadGroup, and look for it and its
            // parents in the hash from ThreadGroup to AppContext --
            // it should be found, because we use createNewContext()
            // when new AppContext objects are created.
            ThreadGroup currentThreadGroup = currentThread.getThreadGroup();
            ThreadGroup threadGroup = currentThreadGroup;
            AppContext context =
                          (AppContext)threadGroup2appContext.get(threadGroup);
            while (context == null) {
                threadGroup = threadGroup.getParent();
                if (threadGroup == null) {
                    // If we get here, we're running under a ThreadGroup that
                    // has no AppContext associated with it.  This should never
                    // happen, because createNewContext() should be used by the
                    // toolkit to create the ThreadGroup that everything runs
                    // under.
                    throw new RuntimeException("Invalid ThreadGroup");
                }
                context = (AppContext)threadGroup2appContext.get(threadGroup);
            }
            // In case we did anything in the above while loop, we add
            // all the intermediate ThreadGroups to threadGroup2appContext
            // so we won't spin again.
            for (ThreadGroup tg = currentThreadGroup; tg != threadGroup; tg = tg.getParent()) {
                threadGroup2appContext.put(tg, context);
            }
            // Now we're done, so we cache the latest key/value pair.
            // (we do this before checking with any AWTSecurityManager, so if
            // this Thread equates with the main AppContext in the cache, it
            // still will)
            mostRecentThreadAppContext =
                new MostRecentThreadAppContext(currentThread, context);

            return context;
          }
         });
        }

        if (appContext == mainAppContext)  {
            // Before we return the main "system" AppContext, check to
            // see if there's an AWTSecurityManager installed.  If so,
            // allow it to choose the AppContext to return.
            SecurityManager securityManager = System.getSecurityManager();
            if ((securityManager != null) &&
                (securityManager instanceof AWTSecurityManager))  {
                AWTSecurityManager awtSecMgr =
                                      (AWTSecurityManager)securityManager;
                AppContext secAppContext = awtSecMgr.getAppContext();
                if (secAppContext != null)  {
                    appContext = secAppContext; // Return what we're told
                }
            }
        }

        return appContext;
    }

    private long DISPOSAL_TIMEOUT = 5000;  // Default to 5-second timeout
                                           // for disposal of all Frames
                                           // (we wait for this time twice,
                                           // once for dispose(), and once
                                           // to clear the EventQueue).

    private long THREAD_INTERRUPT_TIMEOUT = 1000;
                            // Default to 1-second timeout for all
                            // interrupted Threads to exit, and another
                            // 1 second for all stopped Threads to die.

    /**
     * Disposes of this AppContext, all of its top-level Frames, and
     * all Threads and ThreadGroups contained within it.
     * 
     * This method must be called from a Thread which is not contained
     * within this AppContext.
     *
     * @exception  IllegalThreadStateException  if the current thread is
     *                                    contained within this AppContext
     * @since      JDK1.2
     */
    public void dispose() throws IllegalThreadStateException {
        // Check to be sure that the current Thread isn't in this AppContext
        if (this.threadGroup.parentOf(Thread.currentThread().getThreadGroup())) {
            throw new IllegalThreadStateException(
                "Current Thread is contained within AppContext to be disposed."
              );
        }

        synchronized(this) {
            if (this.isDisposed) {
                return; // If already disposed, bail.
            }
            this.isDisposed = true;
        }

        //final PropertyChangeSupport changeSupport = this.changeSupport;
        //if (changeSupport != null) {
        //    changeSupport.firePropertyChange(DISPOSED_PROPERTY_NAME, false, true);
        //}

        // First, we post an InvocationEvent to be run on the
        // EventDispatchThread which disposes of all top-level Frames

        final Object notificationLock = new Object();

        /*no mutiple frames in basis 
        * Runnable runnable = new Runnable() { public void run() {
        *     Frame [] frames = Frame.getFrames();
        *     for (int i = frames.length - 1; i >= 0; i--) {