Add thread management and stepping to runtime

src/engine/sequencer.js

@@ -1,11 +1,17 @@
 var Timer = require('../util/Timer');
 
-function Sequencer () {
+function Sequencer (runtime) {
     /**
      * A utility timer for timing thread sequencing.
      * @type {!Timer}
      */
     this.timer = new Timer();
+
+    /**
+     * Reference to the runtime owning this sequencer.
+     * @type {!Runtime}
+     */
+    this.runtime = runtime;
 }
 
 /**
@@ -18,11 +24,13 @@ Sequencer.WORK_TIME = 1000 / 60;
 
 /**
  * Step through all threads in `this.threads`, running them in order.
- * @return {Array.<Thread>} New threads after this round of execution.
+ * @return {Array.<Thread>} All threads which have finished in this iteration.
  */
 Sequencer.prototype.stepThreads = function (threads) {
     // Start counting toward WORK_TIME
     this.timer.start();
+    // List of threads which have been killed by this step.
+    var inactiveThreads = [];
     // While there are still threads to run and we are within WORK_TIME,
     // continue executing threads.
     while (threads.length > 0 &&
@@ -35,12 +43,14 @@ Sequencer.prototype.stepThreads = function (threads) {
             this.stepThread(activeThread);
             if (activeThread.nextBlock !== null) {
                 newThreads.push(activeThread);
+            } else {
+                inactiveThreads.push(activeThread);
             }
         }
         // Effectively filters out threads that have stopped.
         threads = newThreads;
     }
-    return threads;
+    return inactiveThreads;
 };
 
 /**
@@ -48,7 +58,10 @@ Sequencer.prototype.stepThreads = function (threads) {
  * @param {!Thread} thread Thread object to step
  */
 Sequencer.prototype.stepThread = function (thread) {
-    // @todo
+    // @todo Actually run the blocks
+    // Currently goes to the next block in the sequence.
+    var nextBlock = this.runtime._getNextBlock(thread.nextBlock);
+    thread.nextBlock = nextBlock;
 };
 
 module.exports = Sequencer;