Source for gnu.java.util.prefs.EventDispatcher

   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: }