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	/*
	* Copyright (c) 2007, 2008, 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.awt.image.BufferStrategy;
	import java.lang.ref.WeakReference;

	/**
	* Manages v-synced buffer strategies.
	*/
	public abstract class VSyncedBSManager {

	private static VSyncedBSManager theInstance;

	private static final boolean vSyncLimit =
	Boolean.valueOf((String)java.security.AccessController.doPrivileged(
	new sun.security.action.GetPropertyAction(
	"sun.java2d.vsynclimit", "true")));

	private static VSyncedBSManager getInstance(boolean create) {
	if (theInstance == null && create) {
	theInstance =
	vSyncLimit ? new SingleVSyncedBSMgr() : new NoLimitVSyncBSMgr();
	}
	return theInstance;
	}

	abstract boolean checkAllowed(BufferStrategy bs);
	abstract void relinquishVsync(BufferStrategy bs);

	/**
	* Returns true if the buffer strategy is allowed to be created
	* v-synced.
	*
	* @return true if the bs is allowed to be v-synced, false otherwise
	*/
	public static boolean vsyncAllowed(BufferStrategy bs) {
	VSyncedBSManager bsm = getInstance(true);
	return bsm.checkAllowed(bs);
	}

	/**
	* Lets the manager know that this buffer strategy is no longer interested
	* in being v-synced.
	*/
	public static synchronized void releaseVsync(BufferStrategy bs) {
	VSyncedBSManager bsm = getInstance(false);
	if (bsm != null) {
	bsm.relinquishVsync(bs);
	}
	}

	/**
	* An instance of the manager which allows any buffer strategy to be
	* v-synced.
	*/
	private static final class NoLimitVSyncBSMgr extends VSyncedBSManager {
	@Override
	boolean checkAllowed(BufferStrategy bs) {
	return true;
	}

	@Override
	void relinquishVsync(BufferStrategy bs) {
	}
	}

	/**
	* An instance of the manager which allows only one buffer strategy to
	* be v-synced at any give moment in the vm.
	*/
	private static final class SingleVSyncedBSMgr extends VSyncedBSManager {
	private WeakReference<BufferStrategy> strategy;

	@Override
	public synchronized boolean checkAllowed(BufferStrategy bs) {
	if (strategy != null) {
	BufferStrategy current = strategy.get();
	if (current != null) {
	return (current == bs);
	}
	}
	strategy = new WeakReference<BufferStrategy>(bs);
	return true;
	}

	@Override
	public synchronized void relinquishVsync(BufferStrategy bs) {
	if (strategy != null) {
	BufferStrategy b = strategy.get();
	if (b == bs) {
	strategy.clear();
	strategy = null;
	}
	}
	}
	}
	}

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