/*

 * 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

 * particular file as subject to the "Classpath" exception as provided

 *

 * 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.

 *

 */

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);

        }

    }

}