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	/*
	* Copyright (c) 1999, 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 javax.swing.text;

	import java.util.Vector;
	import sun.awt.AppContext;

	/**
	* A queue of text layout tasks.
	*
	* @author Timothy Prinzing
	* @see AsyncBoxView
	* @since 1.3
	*/
	public class LayoutQueue {

	private static final Object DEFAULT_QUEUE = new Object();

	private Vector<Runnable> tasks;
	private Thread worker;

	/**
	* Construct a layout queue.
	*/
	public LayoutQueue() {
	tasks = new Vector<Runnable>();
	}

	/**
	* Fetch the default layout queue.
	*/
	public static LayoutQueue getDefaultQueue() {
	AppContext ac = AppContext.getAppContext();
	synchronized (DEFAULT_QUEUE) {
	LayoutQueue defaultQueue = (LayoutQueue) ac.get(DEFAULT_QUEUE);
	if (defaultQueue == null) {
	defaultQueue = new LayoutQueue();
	ac.put(DEFAULT_QUEUE, defaultQueue);
	}
	return defaultQueue;
	}
	}

	/**
	* Set the default layout queue.
	*
	* @param q the new queue.
	*/
	public static void setDefaultQueue(LayoutQueue q) {
	synchronized (DEFAULT_QUEUE) {
	AppContext.getAppContext().put(DEFAULT_QUEUE, q);
	}
	}

	/**
	* Add a task that is not needed immediately because
	* the results are not believed to be visible.
	*/
	public synchronized void addTask(Runnable task) {
	if (worker == null) {
	worker = new LayoutThread();
	worker.start();
	}
	tasks.addElement(task);
	notifyAll();
	}

	/**
	* Used by the worker thread to get a new task to execute
	*/
	protected synchronized Runnable waitForWork() {
	while (tasks.size() == 0) {
	try {
	wait();
	} catch (InterruptedException ie) {
	return null;
	}
	}
	Runnable work = tasks.firstElement();
	tasks.removeElementAt(0);
	return work;
	}

	/**
	* low priority thread to perform layout work forever
	*/
	class LayoutThread extends Thread {

	LayoutThread() {
	super("text-layout");
	setPriority(Thread.MIN_PRIORITY);
	}

	public void run() {
	Runnable work;
	do {
	work = waitForWork();
	if (work != null) {
	work.run();
	}
	} while (work != null);
	}


	}

	}

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