Use dynamic count for global thread pool

interface/src/Application.cpp

@@ -176,8 +176,6 @@ static const int MAX_CONCURRENT_RESOURCE_DOWNLOADS = 16;
 // For processing on QThreadPool, target 2 less than the ideal number of threads, leaving
 // 2 logical cores available for time sensitive tasks.
 static const int MIN_PROCESSING_THREAD_POOL_SIZE = 2;
-static const int PROCESSING_THREAD_POOL_SIZE = std::max(MIN_PROCESSING_THREAD_POOL_SIZE,
-                                                        QThread::idealThreadCount() - 2);
 
 static const QString SNAPSHOT_EXTENSION  = ".jpg";
 static const QString SVO_EXTENSION  = ".svo";
@@ -537,7 +535,7 @@ Application::Application(int& argc, char** argv, QElapsedTimer& startupTimer) :
     PluginContainer* pluginContainer = dynamic_cast<PluginContainer*>(this); // set the container for any plugins that care
     PluginManager::getInstance()->setContainer(pluginContainer);
 
-    QThreadPool::globalInstance()->setMaxThreadCount(PROCESSING_THREAD_POOL_SIZE);
+    QThreadPool::globalInstance()->setMaxThreadCount(MIN_PROCESSING_THREAD_POOL_SIZE);
     thread()->setPriority(QThread::HighPriority);
     thread()->setObjectName("Main Thread");
 
@@ -707,6 +705,8 @@ Application::Application(int& argc, char** argv, QElapsedTimer& startupTimer) :
     connect(addressManager.data(), &AddressManager::hostChanged, this, &Application::updateWindowTitle);
     connect(this, &QCoreApplication::aboutToQuit, addressManager.data(), &AddressManager::storeCurrentAddress);
 
+    connect(this, &Application::activeDisplayPluginChanged, this, &Application::updateThreadPoolCount);
+
     // Save avatar location immediately after a teleport.
     connect(getMyAvatar(), &MyAvatar::positionGoneTo,
         DependencyManager::get<AddressManager>().data(), &AddressManager::storeCurrentAddress);
@@ -5727,3 +5727,18 @@ void Application::sendHoverLeaveEntity(QUuid id, PointerEvent event) {
     EntityItemID entityItemID(id);
     emit getEntities()->hoverLeaveEntity(entityItemID, event);
 }
+
+// FIXME?  perhaps two, one for the main thread and one for the offscreen UI rendering thread?
+static const int UI_RESERVED_THREADS = 1;
+// Windows won't let you have all the cores
+static const int OS_RESERVED_THREADS = 1;
+
+void Application::updateThreadPoolCount() const {
+    auto reservedThreads = UI_RESERVED_THREADS + OS_RESERVED_THREADS + _displayPlugin->getRequiredThreadCount();
+    auto availableThreads = QThread::idealThreadCount() - reservedThreads;
+    auto threadPoolSize = std::max(MIN_PROCESSING_THREAD_POOL_SIZE, availableThreads);
+    qDebug() << "Ideal Thread Count " << QThread::idealThreadCount();
+    qDebug() << "Reserved threads " << reservedThreads;
+    qDebug() << "Setting thread pool size to " << threadPoolSize;
+    QThreadPool::globalInstance()->setMaxThreadCount(threadPoolSize);
+}

interface/src/Application.h

@@ -286,6 +286,7 @@ public slots:
     bool exportEntities(const QString& filename, const QVector<EntityItemID>& entityIDs, const glm::vec3* givenOffset = nullptr);
     bool exportEntities(const QString& filename, float x, float y, float z, float scale);
     bool importEntities(const QString& url);
+    void updateThreadPoolCount() const;
 
     static void setLowVelocityFilter(bool lowVelocityFilter);
     Q_INVOKABLE void loadDialog();

libraries/display-plugins/src/display-plugins/OpenGLDisplayPlugin.h

@@ -69,6 +69,8 @@ public:
     virtual bool wantVsync() const { return true; }
     void setVsyncEnabled(bool vsyncEnabled) { _vsyncEnabled = vsyncEnabled; }
     bool isVsyncEnabled() const { return _vsyncEnabled; }
+    // Three threads, one for rendering, one for texture transfers, one reserved for the GL driver
+    int getRequiredThreadCount() const override { return 3; }
 
 protected:
     friend class PresentThread;

libraries/plugins/src/plugins/DisplayPlugin.h

@@ -128,6 +128,7 @@ public:
         Present = QEvent::User + 1
     };
 
+    virtual int getRequiredThreadCount() const { return 0; }
     virtual bool isHmd() const { return false; }
     virtual int getHmdScreen() const { return -1; }
     /// By default, all HMDs are stereo

plugins/openvr/src/OpenVrDisplayPlugin.h

@@ -58,6 +58,9 @@ public:
     void unsuppressKeyboard() override;
     bool isKeyboardVisible() override;
 
+    // Needs an additional thread for VR submission
+    int getRequiredThreadCount() const override { return Parent::getRequiredThreadCount() + 1; }
+
 protected:
     bool internalActivate() override;
     void internalDeactivate() override;