From 173d2a590c4bf265b441824754848590ffdd7480 Mon Sep 17 00:00:00 2001
From: Zach Pomerantz <zach@highfidelity.io>
Date: Fri, 6 May 2016 18:19:10 -0700
Subject: [PATCH] Use sleep_until for ScriptEngine

---
 assignment-client/src/Agent.cpp              |  3 +-
 libraries/script-engine/src/ScriptEngine.cpp | 38 ++++++++++++++++----
 libraries/script-engine/src/ScriptEngine.h   |  4 +--
 3 files changed, 35 insertions(+), 10 deletions(-)

diff --git a/assignment-client/src/Agent.cpp b/assignment-client/src/Agent.cpp
index ef20dc82e2..f8f0f7904a 100644
--- a/assignment-client/src/Agent.cpp
+++ b/assignment-client/src/Agent.cpp
@@ -386,8 +386,7 @@ void Agent::sendAvatarBillboardPacket() {
 void Agent::processAgentAvatarAndAudio(float deltaTime) {
     if (!_scriptEngine->isFinished() && _isAvatar) {
         auto scriptedAvatar = DependencyManager::get<ScriptableAvatar>();
-        const int SCRIPT_AUDIO_BUFFER_SAMPLES = floor(((SCRIPT_DATA_CALLBACK_USECS * AudioConstants::SAMPLE_RATE)
-            / (1000 * 1000)) + 0.5);
+        const int SCRIPT_AUDIO_BUFFER_SAMPLES = AudioConstants::SAMPLE_RATE / SCRIPT_FPS + 0.5;
         const int SCRIPT_AUDIO_BUFFER_BYTES = SCRIPT_AUDIO_BUFFER_SAMPLES * sizeof(int16_t);
 
         QByteArray avatarByteArray = scriptedAvatar->toByteArray(true, randFloat() < AVATAR_SEND_FULL_UPDATE_RATIO);
diff --git a/libraries/script-engine/src/ScriptEngine.cpp b/libraries/script-engine/src/ScriptEngine.cpp
index 6c7739c784..464b514fd5 100644
--- a/libraries/script-engine/src/ScriptEngine.cpp
+++ b/libraries/script-engine/src/ScriptEngine.cpp
@@ -9,6 +9,9 @@
 //  See the accompanying file LICENSE or http://www.apache.org/licenses/LICENSE-2.0.html
 //
 
+#include <chrono>
+#include <thread>
+
 #include <QtCore/QCoreApplication>
 #include <QtCore/QEventLoop>
 #include <QtCore/QFileInfo>
@@ -706,9 +709,15 @@ void ScriptEngine::run() {
 
     QScriptValue result = evaluate(_scriptContents, _fileNameString);
 
-    QElapsedTimer startTime;
-    startTime.start();
+#ifdef _WIN32
+    // VS13 does not sleep_until unless it uses the system_clock, see:
+    // https://www.reddit.com/r/cpp_questions/comments/3o71ic/sleep_until_not_working_with_a_time_pointsteady/
+    using clock = std::chrono::system_clock;
+#else
+    using clock = std::chrono::high_resolution_clock;
+#endif
 
+    clock::time_point startTime = clock::now();
     int thisFrame = 0;
 
     auto nodeList = DependencyManager::get<NodeList>();
@@ -716,12 +725,29 @@ void ScriptEngine::run() {
 
     qint64 lastUpdate = usecTimestampNow();
 
+    // TODO: Integrate this with signals/slots instead of this busy wait
     while (!_isFinished) {
-        int usecToSleep = (thisFrame++ * SCRIPT_DATA_CALLBACK_USECS) - startTime.nsecsElapsed() / 1000; // nsec to usec
-        if (usecToSleep > 0) {
-            usleep(usecToSleep);
-        }
+        // Throttle to SCRIPT_FPS
+        const std::chrono::microseconds FRAME_DURATION(USECS_PER_SECOND / SCRIPT_FPS + 1);
+        clock::time_point sleepTime(startTime + thisFrame++ * FRAME_DURATION);
+        std::this_thread::sleep_until(sleepTime);
 
+#ifdef SCRIPT_DELAY_DEBUG
+        {
+            auto now = clock::now();
+            uint64_t seconds = std::chrono::duration_cast<std::chrono::seconds>(now - startTime).count();
+            if (seconds > 0) { // avoid division by zero and time travel
+                uint64_t fps = thisFrame / seconds;
+                // Overreporting artificially reduces the reported rate
+                if (thisFrame % SCRIPT_FPS == 0) {
+                    qCDebug(scriptengine) <<
+                        "Frame:" << thisFrame <<
+                        "Slept (us):" << std::chrono::duration_cast<std::chrono::microseconds>(now - sleepTime).count() <<
+                        "FPS:" << fps;
+                }
+            }
+        }
+#endif
         if (_isFinished) {
             break;
         }
diff --git a/libraries/script-engine/src/ScriptEngine.h b/libraries/script-engine/src/ScriptEngine.h
index 175a3f1f1c..f050997235 100644
--- a/libraries/script-engine/src/ScriptEngine.h
+++ b/libraries/script-engine/src/ScriptEngine.h
@@ -39,9 +39,9 @@
 #include "ScriptUUID.h"
 #include "Vec3.h"
 
-const QString NO_SCRIPT("");
+static const QString NO_SCRIPT("");
 
-const unsigned int SCRIPT_DATA_CALLBACK_USECS = floor(((1.0f / 60.0f) * 1000 * 1000) + 0.5f);
+static const int SCRIPT_FPS = 60;
 
 class CallbackData {
 public: