001    /* LayoutQueue.java --
002       Copyright (C) 2005  Free Software Foundation, Inc.
003    
004    This file is part of GNU Classpath.
005    
006    GNU Classpath is free software; you can redistribute it and/or modify
007    it under the terms of the GNU General Public License as published by
008    the Free Software Foundation; either version 2, or (at your option)
009    any later version.
010    
011    GNU Classpath is distributed in the hope that it will be useful, but
012    WITHOUT ANY WARRANTY; without even the implied warranty of
013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014    General Public License for more details.
015    
016    You should have received a copy of the GNU General Public License
017    along with GNU Classpath; see the file COPYING.  If not, write to the
018    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019    02110-1301 USA.
020    
021    Linking this library statically or dynamically with other modules is
022    making a combined work based on this library.  Thus, the terms and
023    conditions of the GNU General Public License cover the whole
024    combination.
025    
026    As a special exception, the copyright holders of this library give you
027    permission to link this library with independent modules to produce an
028    executable, regardless of the license terms of these independent
029    modules, and to copy and distribute the resulting executable under
030    terms of your choice, provided that you also meet, for each linked
031    independent module, the terms and conditions of the license of that
032    module.  An independent module is a module which is not derived from
033    or based on this library.  If you modify this library, you may extend
034    this exception to your version of the library, but you are not
035    obligated to do so.  If you do not wish to do so, delete this
036    exception statement from your version. */
037    
038    
039    package javax.swing.text;
040    
041    import java.util.LinkedList;
042    
043    /**
044     * This is a queue which holds {@link Runnable} objects.  It is
045     * intended for deferring layout operations.
046     */
047    public class LayoutQueue
048    {
049      // The default layout queue.
050      private static LayoutQueue defaultQueue = new LayoutQueue();
051    
052      // The queue of tasks.
053      private LinkedList list = new LinkedList();
054    
055      /**
056       * Create a new layout queue.
057       */
058      public LayoutQueue()
059      {
060        // Nothing to do here.
061      }
062    
063      /**
064       * Add a layout task to the queue.
065       */
066      public void addTask(Runnable task)
067      {
068        synchronized (list)
069          {
070            list.addLast(task);
071            list.notify();
072          }
073      }
074    
075      /**
076       * Called by a worker thread to retrieve the next layout task.  This
077       * will block until a new task is available.  This method will
078       * return null if the thread is interrupted while waiting.
079       */
080      protected Runnable waitForWork()
081      {
082        synchronized (list)
083          {
084            while (list.size() == 0)
085              {
086                try
087                  {
088                    list.wait();
089                  }
090                catch (InterruptedException _)
091                  {
092                    // This seemed like a good idea, but it has not been
093                    // tested on the JDK.
094                    return null;
095                  }
096              }
097            return (Runnable) list.removeFirst();
098          }
099      }
100    
101      /**
102       * Return the default layout queue.
103       */
104      public static synchronized LayoutQueue getDefaultQueue()
105      {
106        return defaultQueue;
107      }
108    
109      /**
110       * Set the default layout queue.
111       */
112      public static synchronized void setDefaultQueue(LayoutQueue q)
113      {
114        defaultQueue = q;
115      }
116    }