From 55ac7e269cd3a49262e05883dfecf0f31f8d19ce Mon Sep 17 00:00:00 2001
From: Ray Schamp <ray@scratch.mit.edu>
Date: Wed, 23 Nov 2016 15:47:49 -0500
Subject: [PATCH] Add PROJECT_RUN_START/STOP events

These events signal when any threads are running or when all threads have stopped running. This maps to whether the green flag or the stop button should be illuminated in the GUI.
---
 src/engine/runtime.js | 33 +++++++++++++++++++++++++++++++++
 src/index.js          |  5 +++++
 2 files changed, 38 insertions(+)

diff --git a/src/engine/runtime.js b/src/engine/runtime.js
index a8bd98c5..6e4c0c87 100644
--- a/src/engine/runtime.js
+++ b/src/engine/runtime.js
@@ -83,6 +83,12 @@ var Runtime = function () {
      */
     this._scriptGlowsPreviousFrame = [];
 
+    /**
+     * Number of threads running during the previous frame
+     * @type {number}
+     */
+    this._threadCount = 0;
+
     /**
      * Currently known number of clones, used to enforce clone limit.
      * @type {number}
@@ -179,6 +185,18 @@ Runtime.BLOCK_GLOW_ON = 'BLOCK_GLOW_ON';
  */
 Runtime.BLOCK_GLOW_OFF = 'BLOCK_GLOW_OFF';
 
+/**
+ * Event name for glowing the green flag
+ * @const {string}
+ */
+Runtime.PROJECT_RUN_START = 'PROJECT_RUN_START'
+
+/**
+ * Event name for unglowing the green flag
+ * @const {string}
+ */
+Runtime.PROJECT_RUN_STOP = 'PROJECT_RUN_STOP'
+
 /**
  * Event name for visual value report.
  * @const {string}
@@ -552,6 +570,7 @@ Runtime.prototype._step = function () {
     this.redrawRequested = false;
     var inactiveThreads = this.sequencer.stepThreads();
     this._updateGlows(inactiveThreads);
+    this._setThreadCount(this.threads.length);
     if (this.renderer) {
         // @todo: Only render when this.redrawRequested or clones rendered.
         this.renderer.draw();
@@ -639,6 +658,20 @@ Runtime.prototype._updateGlows = function (optExtraThreads) {
     this._scriptGlowsPreviousFrame = finalScriptGlows;
 };
 
+/**
+ * Emit run start/stop after each tick. Emits when `this.threads.length` goes
+ * between non-zero and zero
+ */
+Runtime.prototype._setThreadCount = function (threadCount) {
+    if (this._threadCount === 0 && threadCount > 0) {
+        this.emit(Runtime.PROJECT_RUN_START);
+    }
+    if (this._threadCount > 0 && threadCount === 0) {
+        this.emit(Runtime.PROJECT_RUN_STOP);
+    }
+    this._threadCount = threadCount;
+};
+
 /**
  * "Quiet" a script's glow: stop the VM from generating glow/unglow events
  * about that script. Use when a script has just been deleted, but we may
diff --git a/src/index.js b/src/index.js
index 8b390f35..4ed724f3 100644
--- a/src/index.js
+++ b/src/index.js
@@ -37,6 +37,11 @@ var VirtualMachine = function () {
     instance.runtime.on(Runtime.BLOCK_GLOW_OFF, function (glowData) {
         instance.emit(Runtime.BLOCK_GLOW_OFF, glowData);
     });
+    instance.runtime.on(Runtime.PROJECT_RUN_START, function () {
+        instance.emit(Runtime.PROJECT_RUN_START);
+    });
+    instance.runtime.on(Runtime.PROJECT_RUN_STOP, function () {
+        instance.emit(Runtime.PROJECT_RUN_STOP);
     });
     instance.runtime.on(Runtime.VISUAL_REPORT, function (visualReport) {
         instance.emit(Runtime.VISUAL_REPORT, visualReport);