src/org/xwt/Scheduler.java

   1 // Copyright 2004 Adam Megacz, see the COPYING file for licensing [GPL]
   2 package org.xwt;
   3
   4 import java.util.*;
   5 import org.xwt.js.*;
   6 import org.xwt.util.*;
   7
   8 /** Implements cooperative multitasking */
   9 public class Scheduler {
  10
  11     // Public API Exposed to org.xwt /////////////////////////////////////////////////
  12
  13     private static Scheduler singleton;
  14     public static interface Task { public abstract void perform() throws Exception; }
  15     public static void add(Task t) { singleton.runnable.append(t); }
  16     public static void init() { if (singleton == null) (singleton = Platform.getScheduler()).run(); }
  17
  18     private static Task current = null;
  19
  20     private static volatile boolean rendering = false;
  21     private static volatile boolean again = false;
  22
  23     /** synchronizd so that we can safely call it from an event-delivery thread, in-context */
  24     public static void renderAll() {
  25         if (rendering) { again = true; return; }
  26         synchronized(Scheduler.class) {
  27             try {
  28                 rendering = true;
  29                 do {
  30                     // FEATURE: this could be cleaner
  31                     again = false;
  32                     for(int i=0; i<Surface.allSurfaces.size(); i++) {
  33                         Surface s = ((Surface)Surface.allSurfaces.elementAt(i));
  34                         do { s.render(); } while(s.abort);
  35                     }
  36                 } while(again);
  37             } finally {
  38                 rendering = false;
  39             }
  40         }
  41     }
  42
  43
  44
  45     // API which must be supported by subclasses /////////////////////////////////////
  46
  47     /**
  48      *  SCHEDULER INVARIANT: all scheduler implementations MUST invoke
  49      *  Surface.renderAll() after performing a Task if no tasks remain
  50      *  in the queue.  A scheduler may choose to invoke
  51      *  Surface.renderAll() more often than that if it so chooses.
  52      */
  53     public void run() { defaultRun(); }
  54     protected Scheduler() { }
  55
  56
  57     // Default Implementation //////////////////////////////////////////////////////
  58
  59     protected static Queue runnable = new Queue(50);
  60     public void defaultRun() {
  61         while(true) {
  62             current = (Task)runnable.remove(true);
  63             try {
  64                 // FIXME hideous
  65                 synchronized(this) {
  66                     for(int i=0; i<Surface.allSurfaces.size(); i++) {
  67                         Surface s = (Surface)Surface.allSurfaces.elementAt(i);
  68                         if (current instanceof JS) {
  69                             s._mousex = Integer.MAX_VALUE;
  70                             s._mousey = Integer.MAX_VALUE;
  71                         } else {
  72                             s._mousex = s.mousex;
  73                             s._mousey = s.mousey;
  74                         }
  75                     }
  76                     current.perform();
  77                 }
  78                 renderAll();
  79             } catch (JSExn e) {
  80                 Log.info(Scheduler.class, "a JavaScript thread spawned with xwt.thread() threw an exception:");
  81                 Log.info(Scheduler.class, "JS Exception: " + e.getObject() + "\n" + e.backtrace());
  82                 Log.info(Scheduler.class,e);
  83             } catch (Exception e) {
  84                 Log.info(Scheduler.class, "a Task threw an exception which was caught by the scheduler:");
  85                 Log.info(Scheduler.class, e);
  86             }
  87             // if an Error is thrown it will cause the engine to quit
  88         }
  89     }
  90 }