1 /*

     2  * Copyright (c) 1999, 2008, Oracle and/or its affiliates. All rights reserved.

     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

     4  *

     5  * This code is free software; you can redistribute it and/or modify it

     6  * under the terms of the GNU General Public License version 2 only, as

     7  * published by the Free Software Foundation.  Oracle designates this

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

     9  * by Oracle in the LICENSE file that accompanied this code.

    10  *

    11  * This code is distributed in the hope that it will be useful, but WITHOUT

    12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

    13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

    14  * version 2 for more details (a copy is included in the LICENSE file that

    15  * accompanied this code).

    16  *

    17  * You should have received a copy of the GNU General Public License version

    18  * 2 along with this work; if not, write to the Free Software Foundation,

    19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    20  *

    21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

    22  * or visit www.oracle.com if you need additional information or have any

    23  * questions.

    24  */

    25 package javax.swing.text;

    26 

    27 import java.util.Vector;

    28 import sun.awt.AppContext;

    29 

    30 /**

    31  * A queue of text layout tasks.

    32  *

    33  * @author  Timothy Prinzing

    34  * @see     AsyncBoxView

    35  * @since   1.3

    36  */

    37 public class LayoutQueue {

    38 

    39     private static final Object DEFAULT_QUEUE = new Object();

    40 

    41     private Vector<Runnable> tasks;

    42     private Thread worker;

    43 

    44     /**

    45      * Construct a layout queue.

    46      */

    47     public LayoutQueue() {

    48         tasks = new Vector<Runnable>();

    49     }

    50 

    51     /**

    52      * Fetch the default layout queue.

    53      */

    54     public static LayoutQueue getDefaultQueue() {

    55         AppContext ac = AppContext.getAppContext();

    56         synchronized (DEFAULT_QUEUE) {

    57             LayoutQueue defaultQueue = (LayoutQueue) ac.get(DEFAULT_QUEUE);

    58             if (defaultQueue == null) {

    59                 defaultQueue = new LayoutQueue();

    60                 ac.put(DEFAULT_QUEUE, defaultQueue);

    61             }

    62             return defaultQueue;

    63         }

    64     }

    65 

    66     /**

    67      * Set the default layout queue.

    68      *

    69      * @param q the new queue.

    70      */

    71     public static void setDefaultQueue(LayoutQueue q) {

    72         synchronized (DEFAULT_QUEUE) {

    73             AppContext.getAppContext().put(DEFAULT_QUEUE, q);

    74         }

    75     }

    76 

    77     /**

    78      * Add a task that is not needed immediately because

    79      * the results are not believed to be visible.

    80      */

    81     public synchronized void addTask(Runnable task) {

    82         if (worker == null) {

    83             worker = new LayoutThread();

    84             worker.start();

    85         }

    86         tasks.addElement(task);

    87         notifyAll();

    88     }

    89 

    90     /**

    91      * Used by the worker thread to get a new task to execute

    92      */

    93     protected synchronized Runnable waitForWork() {

    94         while (tasks.size() == 0) {

    95             try {

    96                 wait();

    97             } catch (InterruptedException ie) {

    98                 return null;

    99             }

   100         }

   101         Runnable work = tasks.firstElement();

   102         tasks.removeElementAt(0);

   103         return work;

   104     }

   105 

   106     /**

   107      * low priority thread to perform layout work forever

   108      */

   109     class LayoutThread extends Thread {

   110 

   111         LayoutThread() {

   112             super("text-layout");

   113             setPriority(Thread.MIN_PRIORITY);

   114         }

   115 

   116         public void run() {

   117             Runnable work;

   118             do {

   119                 work = waitForWork();

   120                 if (work != null) {

   121                     work.run();

   122                 }

   123             } while (work != null);

   124         }

   125 

   126 

   127     }

   128 

   129 }