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	/*
	* Copyright (c) 1995, 2012, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code 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. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code 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 in the LICENSE file that
	* accompanied this code).
	*
	* 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	package sun.awt.image;

	import java.lang.ref.WeakReference;
	import java.awt.Image;
	import java.awt.image.ImageObserver;

	import java.security.AccessControlContext;
	import java.security.AccessController;
	import java.security.PrivilegedAction;

	public abstract class ImageWatched {
	public static Link endlink = new Link();

	public Link watcherList;

	public ImageWatched() {
	watcherList = endlink;
	}

	/*
	* This class defines a node on a linked list of ImageObservers.
	* The base class defines the dummy implementation used for the
	* last link on all chains and a subsequent subclass then
	* defines the standard implementation that manages a weak
	* reference to a real ImageObserver.
	*/
	public static class Link {
	/*
	* Check if iw is the referent of this Link or any
	* subsequent Link objects on this chain.
	*/
	public boolean isWatcher(ImageObserver iw) {
	return false; // No "iw" down here.
	}

	/*
	* Remove this Link from the chain if its referent
	* is the indicated target or if it has been nulled
	* out by the garbage collector.
	* Return the new remainder of the chain.
	* The argument may be null which will trigger
	* the chain to remove only the dead (null) links.
	* This method is only ever called inside a
	* synchronized block so Link.next modifications
	* will be safe.
	*/
	public Link removeWatcher(ImageObserver iw) {
	return this; // Leave me as the end link.
	}

	/*
	* Deliver the indicated image update information
	* to the referent of this Link and return a boolean
	* indicating whether or not some referent became
	* null or has indicated a lack of interest in
	* further updates to its imageUpdate() method.
	* This method is not called inside a synchronized
	* block so Link.next modifications are not safe.
	*/
	public boolean newInfo(Image img, int info,
	int x, int y, int w, int h)
	{
	return false; // No disinterested parties down here.
	}
	}

	static class AccWeakReference<T> extends WeakReference<T> {

	private final AccessControlContext acc;

	AccWeakReference(T ref) {
	super(ref);
	acc = AccessController.getContext();
	}
	}

	/*
	* Standard Link implementation to manage a Weak Reference
	* to an ImageObserver.
	*/
	public static class WeakLink extends Link {
	private final AccWeakReference<ImageObserver> myref;
	private Link next;

	public WeakLink(ImageObserver obs, Link next) {
	myref = new AccWeakReference<ImageObserver>(obs);
	this.next = next;
	}

	public boolean isWatcher(ImageObserver iw) {
	return (myref.get() == iw \|\| next.isWatcher(iw));
	}

	public Link removeWatcher(ImageObserver iw) {
	ImageObserver myiw = myref.get();
	if (myiw == null) {
	// Remove me from the chain, but continue recursion.
	return next.removeWatcher(iw);
	}
	// At this point myiw is not null so we know this test will
	// never succeed if this is a pruning pass (iw == null).
	if (myiw == iw) {
	// Remove me from the chain and end the recursion here.
	return next;
	}
	// I am alive, but not the one to be removed, recurse
	// and update my next link and leave me in the chain.
	next = next.removeWatcher(iw);
	return this;
	}

	private static boolean update(ImageObserver iw, AccessControlContext acc,
	Image img, int info,
	int x, int y, int w, int h) {

	if (acc != null \|\| System.getSecurityManager() != null) {
	return AccessController.doPrivileged(
	(PrivilegedAction<Boolean>) () -> {
	return iw.imageUpdate(img, info, x, y, w, h);
	}, acc);
	}
	return false;
	}

	public boolean newInfo(Image img, int info,
	int x, int y, int w, int h)
	{
	// Note tail recursion because items are added LIFO.
	boolean ret = next.newInfo(img, info, x, y, w, h);
	ImageObserver myiw = myref.get();
	if (myiw == null) {
	// My referent is null so we must prune in a second pass.
	ret = true;
	} else if (update(myiw, myref.acc, img, info, x, y, w, h) == false) {
	// My referent has lost interest so clear it and ask
	// for a pruning pass to remove it later.
	myref.clear();
	ret = true;
	}
	return ret;
	}
	}

	public synchronized void addWatcher(ImageObserver iw) {
	if (iw != null && !isWatcher(iw)) {
	watcherList = new WeakLink(iw, watcherList);
	}
	watcherList = watcherList.removeWatcher(null);
	}

	public synchronized boolean isWatcher(ImageObserver iw) {
	return watcherList.isWatcher(iw);
	}

	public void removeWatcher(ImageObserver iw) {
	synchronized (this) {
	watcherList = watcherList.removeWatcher(iw);
	}
	if (watcherList == endlink) {
	notifyWatcherListEmpty();
	}
	}

	public boolean isWatcherListEmpty() {
	synchronized (this) {
	watcherList = watcherList.removeWatcher(null);
	}
	return (watcherList == endlink);
	}

	public void newInfo(Image img, int info, int x, int y, int w, int h) {
	if (watcherList.newInfo(img, info, x, y, w, h)) {
	// Some Link returned true so we now need to prune dead links.
	removeWatcher(null);
	}
	}

	protected abstract void notifyWatcherListEmpty();
	}

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