libjava/classpath/gnu/java/util/prefs/EventDispatcher.java

   1 /* EventDispatcher.java -- Dispatch events for prefs
   2    Copyright (C) 2006 Free Software Foundation, Inc.
   3
   4 This file is part of GNU Classpath.
   5
   6 GNU Classpath is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GNU Classpath is distributed in the hope that it will be useful, but
  12 WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Classpath; see the file COPYING.  If not, write to the
  18 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  19 02110-1301 USA.
  20
  21 Linking this library statically or dynamically with other modules is
  22 making a combined work based on this library.  Thus, the terms and
  23 conditions of the GNU General Public License cover the whole
  24 combination.
  25
  26 As a special exception, the copyright holders of this library give you
  27 permission to link this library with independent modules to produce an
  28 executable, regardless of the license terms of these independent
  29 modules, and to copy and distribute the resulting executable under
  30 terms of your choice, provided that you also meet, for each linked
  31 independent module, the terms and conditions of the license of that
  32 module.  An independent module is a module which is not derived from
  33 or based on this library.  If you modify this library, you may extend
  34 this exception to your version of the library, but you are not
  35 obligated to do so.  If you do not wish to do so, delete this
  36 exception statement from your version. */
  37
  38
  39 package gnu.java.util.prefs;
  40
  41 import java.util.ArrayList;
  42
  43 /**
  44  * This is a helper class used for dispatching events for
  45  * the prefs package.
  46  */
  47 public class EventDispatcher extends Thread
  48 {
  49   // This is a singleton class.  We dispatch all events via a
  50   // new Thread which is created on demand.
  51   private static final Thread dispatchThread = new EventDispatcher();
  52
  53   // This is a queue of events to dispatch.  This thread waits on
  54   // the queue and when notified will remove events until the queue
  55   // is empty.
  56   private static final ArrayList<Runnable> queue = new ArrayList<Runnable>();
  57
  58   // FIXME: this thread probably ought to go in some classpath-internal
  59   // ThreadGroup.  But we don't have that yet.
  60   private EventDispatcher()
  61   {
  62     setDaemon(true);
  63     start();
  64   }
  65
  66   public void run()
  67   {
  68     while (true)
  69       {
  70         Runnable r;
  71         synchronized (queue)
  72           {
  73             while (queue.size() == 0)
  74               {
  75                 try
  76                   {
  77                     queue.wait();
  78                   }
  79                 catch (InterruptedException _)
  80                   {
  81                     // Ignore.
  82                   }
  83               }
  84             r = queue.remove(0);
  85           }
  86         // Invoke outside the synchronization, so that
  87         // we aren't blocking other threads from posting events.
  88         try
  89           {
  90             r.run();
  91           }
  92         catch (Throwable _)
  93           {
  94             // Ignore.
  95           }
  96       }
  97   }
  98
  99   /**
 100    * Add a new runnable to the event dispatch queue.  The
 101    * runnable will be invoked in the event dispatch queue
 102    * without any locks held.
 103    * @param runner the Runnable to dispatch
 104    */
 105   public static void dispatch(Runnable runner)
 106   {
 107     synchronized (queue)
 108       {
 109         queue.add(runner);
 110         queue.notify();
 111       }
 112   }
 113 }