/*

 * Copyright 1999 Sun Microsystems, Inc.  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.  Sun designates this

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

 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.com if you need additional information or

 * have any questions.

 */

package javax.swing.text;

import java.util.Vector;

/**

 * A queue of text layout tasks.

 *

 * @author  Timothy Prinzing

 * @see     AsyncBoxView

 * @since   1.3

 */

public class LayoutQueue {

    Thread worker;

    static LayoutQueue defaultQueue;

    /**

     * Construct a layout queue.

     */

    public LayoutQueue() {

    }

    /**

     * Fetch the default layout queue.

     */

    public static LayoutQueue getDefaultQueue() {

        if (defaultQueue == null) {

            defaultQueue = new LayoutQueue();

        }

        return defaultQueue;

    }

    /**

     * Set the default layout queue.

     *

     * @param q the new queue.

     */

    public static void setDefaultQueue(LayoutQueue q) {

        defaultQueue = 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;

            }

        }

        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);

        }

    }

}