001/* LayoutQueue.java --
002   Copyright (C) 2005  Free Software Foundation, Inc.
003
004This file is part of GNU Classpath.
005
006GNU Classpath is free software; you can redistribute it and/or modify
007it under the terms of the GNU General Public License as published by
008the Free Software Foundation; either version 2, or (at your option)
009any later version.
010
011GNU Classpath is distributed in the hope that it will be useful, but
012WITHOUT ANY WARRANTY; without even the implied warranty of
013MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014General Public License for more details.
015
016You should have received a copy of the GNU General Public License
017along with GNU Classpath; see the file COPYING.  If not, write to the
018Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
01902110-1301 USA.
020
021Linking this library statically or dynamically with other modules is
022making a combined work based on this library.  Thus, the terms and
023conditions of the GNU General Public License cover the whole
024combination.
025
026As a special exception, the copyright holders of this library give you
027permission to link this library with independent modules to produce an
028executable, regardless of the license terms of these independent
029modules, and to copy and distribute the resulting executable under
030terms of your choice, provided that you also meet, for each linked
031independent module, the terms and conditions of the license of that
032module.  An independent module is a module which is not derived from
033or based on this library.  If you modify this library, you may extend
034this exception to your version of the library, but you are not
035obligated to do so.  If you do not wish to do so, delete this
036exception statement from your version. */
037
038
039package javax.swing.text;
040
041import java.util.LinkedList;
042
043/**
044 * This is a queue which holds {@link Runnable} objects.  It is
045 * intended for deferring layout operations.
046 */
047public 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}