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
  16     /** adds a task to the back of the queue */
  17     public static void add(Task t) { singleton.runnable.append(t); }
  18
  19     public static void init() { if (singleton == null) (singleton = Platform.getScheduler()).run(); }
  20
  21     private static Task currentTask = null;
  22     public static Task current() { return currentTask; }
  23
  24     /** synchronizd so that we can safely call it from an event-delivery thread, in-context */
  25     private static volatile boolean rendering = false;
  26     private static volatile boolean again = false;
  27     public static void renderAll() {
  28         if (rendering) { again = true; return; }
  29         synchronized(Scheduler.class) {
  30             try {
  31                 rendering = true;
  32                 do {
  33                     again = false;
  34                     for(int i=0; i<Surface.allSurfaces.size(); i++) {
  35                         Surface s = ((Surface)Surface.allSurfaces.elementAt(i));
  36                         do { s.render(); } while(s.abort);
  37                     }
  38                 } while(again);
  39             } finally {
  40                 rendering = false;
  41             }
  42         }
  43     }
  44
  45
  46
  47     // API which must be supported by subclasses /////////////////////////////////////
  48
  49     /**
  50      *  SCHEDULER INVARIANT: all scheduler implementations MUST invoke
  51      *  Surface.renderAll() after performing a Task if no tasks remain
  52      *  in the queue.  A scheduler may choose to invoke
  53      *  Surface.renderAll() more often than that if it so chooses.
  54      */
  55     public void run() { defaultRun(); }
  56     protected Scheduler() { }
  57
  58
  59     // Default Implementation //////////////////////////////////////////////////////
  60
  61     protected static Queue runnable = new Queue(50);
  62     public void defaultRun() {
  63         try {while(true) {
  64             currentTask = (Task)runnable.remove(true);
  65             try {
  66                 synchronized(this) {
  67                     for(int i=0; i<Surface.allSurfaces.size(); i++) {
  68                         Surface s = (Surface)Surface.allSurfaces.elementAt(i);
  69                         if (currentTask instanceof JS) {
  70                             s._mousex = Integer.MAX_VALUE;
  71                             s._mousey = Integer.MAX_VALUE;
  72                         } else {
  73                             s._mousex = s.mousex;
  74                             s._mousey = s.mousey;
  75                         }
  76                     }
  77                     currentTask.perform();
  78                 }
  79                 renderAll();
  80             } catch (JSExn e) {
  81                 Log.info(Scheduler.class, "a JavaScript thread spawned with xwt.thread() threw an exception:");
  82                 Log.info(Scheduler.class, "JS Exception: " + e.getObject() + "\n" + e.backtrace());
  83                 Log.info(Scheduler.class,e);
  84             } catch (Exception e) {
  85                 Log.info(Scheduler.class, "a Task threw an exception which was caught by the scheduler:");
  86                 Log.info(Scheduler.class, e);
  87             }
  88             // if an Error is thrown it will cause the engine to quit
  89 }        } catch (Throwable t) {
  90             t.printStackTrace();
  91         }
  92     }
  93 }