import org.xwt.js.*;
import org.xwt.util.*;
-// FEATURE: reimplement Watcher
/** Implements cooperative multitasking */
public class Scheduler {
- private static Scheduler singleton = new Scheduler();
- public static void run() { singleton.do_run(); }
+ // Public API Exposed to org.xwt /////////////////////////////////////////////////
+
+ private static Scheduler singleton;
+ public static interface Task { public abstract void perform() throws Exception; }
+
+ /** adds a task to the back of the queue */
+ public static void add(Task t) { singleton.runnable.append(t); }
+
+ /** adds a task to the front of the queue (guaranteed to run next) */
+ public static void addAtFront(Task t) { singleton.runnable.prepend(t); }
+
+ public static void init() { if (singleton == null) (singleton = Platform.getScheduler()).run(); }
+
+ // API which must be supported by subclasses /////////////////////////////////////
+
+ /**
+ * SCHEDULER INVARIANT: all scheduler implementations MUST invoke
+ * Surface.renderAll() after performing a Task if no tasks remain
+ * in the queue. A scheduler may choose to invoke
+ * Surface.renderAll() more often than that if it so chooses.
+ */
+ public void run() { defaultRun(); }
protected Scheduler() { }
- public static abstract class Task implements Callback { public abstract Object call(Object o); }
- private static Queue runnable = new Queue(50);
+ // Default Implementation //////////////////////////////////////////////////////
- public static void add(Task t) { singleton.runnable.append(t); }
- public void do_run() {
+ protected static Queue runnable = new Queue(50);
+ public void defaultRun() {
while(true) {
Task t = (Task)runnable.remove(true);
try {
- t.call(null);
- for(int i=0; i<Surface.allSurfaces.size(); i++)
- ((Surface)Surface.allSurfaces.elementAt(i)).render();
+ t.perform();
+ // FEATURE: be smarter about this
+ if (t != Surface.renderAll) add(Surface.renderAll);
+ } catch (JSExn e) {
+ Log.log(Scheduler.class, "a JavaScript thread spawned with xwt.thread() threw an exception:");
+ Log.log(Scheduler.class, e.toString());
} catch (Exception e) {
- Log.log(Scheduler.class, "Task threw an exception: " + e);
+ Log.log(Scheduler.class, "a Task threw an exception which was caught by the scheduler:");
Log.log(Scheduler.class, e);
}
+ // if an Error is thrown it will cause the engine to quit
}
}
}