Merge pull request #11593 from hyperlogic/bug-fix/reduce-pressure-on-event-queue

Reduce present traffic on main thread event queue.

interface/src/Application.cpp

@@ -207,6 +207,17 @@
 #if defined(Q_OS_WIN)
 #include <VersionHelpers.h>
 
+#ifdef DEBUG_EVENT_QUEUE
+// This is a HACK that uses private headers included with the qt source distrubution.
+// To use this feature you need to add these directores to your include path:
+// E:/Qt/5.9.1/Src/qtbase/include/QtCore/5.9.1/QtCore
+// E:/Qt/5.9.1/Src/qtbase/include/QtCore/5.9.1
+#define QT_BOOTSTRAPPED
+#include <private/qthread_p.h>
+#include <private/qobject_p.h>
+#undef QT_BOOTSTRAPPED
+#endif
+
 extern "C" {
  _declspec(dllexport) DWORD NvOptimusEnablement = 0x00000001;
 }
@@ -264,9 +275,7 @@ private:
         switch ((int)event->type()) {
             case ApplicationEvent::Render:
                 render();
-                // Ensure we never back up the render events.  Each render should be triggered only in response
-                // to the NEXT render event after the last render occured
-                QCoreApplication::removePostedEvents(this, ApplicationEvent::Render);
+                qApp->_pendingRenderEvent.store(false);
                 return true;
 
             default:
@@ -2712,9 +2721,14 @@ bool Application::importFromZIP(const QString& filePath) {
     return true;
 }
 
+// thread-safe
 void Application::onPresent(quint32 frameCount) {
-    postEvent(this, new QEvent((QEvent::Type)ApplicationEvent::Idle), Qt::HighEventPriority);
-    if (_renderEventHandler && !isAboutToQuit()) {
+    bool expected = false;
+    if (_pendingIdleEvent.compare_exchange_strong(expected, true)) {
+        postEvent(this, new QEvent((QEvent::Type)ApplicationEvent::Idle), Qt::HighEventPriority);
+    }
+    expected = false;
+    if (_renderEventHandler && !isAboutToQuit() && _pendingRenderEvent.compare_exchange_strong(expected, true)) {
         postEvent(_renderEventHandler, new QEvent((QEvent::Type)ApplicationEvent::Render));
     }
 }
@@ -2781,7 +2795,26 @@ bool Application::handleFileOpenEvent(QFileOpenEvent* fileEvent) {
     return false;
 }
 
+#ifdef DEBUG_EVENT_QUEUE
+static int getEventQueueSize(QThread* thread) {
+    auto threadData = QThreadData::get2(thread);
+    QMutexLocker locker(&threadData->postEventList.mutex);
+    return threadData->postEventList.size();
+}
+
+static void dumpEventQueue(QThread* thread) {
+    auto threadData = QThreadData::get2(thread);
+    QMutexLocker locker(&threadData->postEventList.mutex);
+    qDebug() << "AJT: event list, size =" << threadData->postEventList.size();
+    for (auto& postEvent : threadData->postEventList) {
+        QEvent::Type type = (postEvent.event ? postEvent.event->type() : QEvent::None);
+        qDebug() << "AJT:    " << type;
+    }
+}
+#endif // DEBUG_EVENT_QUEUE
+
 bool Application::event(QEvent* event) {
+
     if (!Menu::getInstance()) {
         return false;
     }
@@ -2801,8 +2834,18 @@ bool Application::event(QEvent* event) {
         // see (windowMinimizedChanged)
         case ApplicationEvent::Idle:
             idle();
-            // Don't process extra idle events that arrived in the event queue while we were doing this idle
-            QCoreApplication::removePostedEvents(this, ApplicationEvent::Idle);
+
+#ifdef DEBUG_EVENT_QUEUE
+            {
+                int count = getEventQueueSize(QThread::currentThread());
+                if (count > 400) {
+                    dumpEventQueue(QThread::currentThread());
+                }
+            }
+#endif // DEBUG_EVENT_QUEUE
+
+            _pendingIdleEvent.store(false);
+
             return true;
 
         case QEvent::MouseMove:
@@ -7203,7 +7246,7 @@ void Application::updateDisplayMode() {
         _offscreenContext->makeCurrent();
         getApplicationCompositor().setDisplayPlugin(newDisplayPlugin);
         _displayPlugin = newDisplayPlugin;
-        connect(_displayPlugin.get(), &DisplayPlugin::presented, this, &Application::onPresent);
+        connect(_displayPlugin.get(), &DisplayPlugin::presented, this, &Application::onPresent, Qt::DirectConnection);
         auto desktop = offscreenUi->getDesktop();
         if (desktop) {
             desktop->setProperty("repositionLocked", wasRepositionLocked);

interface/src/Application.h

@@ -717,5 +717,8 @@ private:
     LaserPointerManager _laserPointerManager;
 
     friend class RenderEventHandler;
+
+    std::atomic<bool> _pendingIdleEvent { false };
+    std::atomic<bool> _pendingRenderEvent { false };
 };
 #endif // hifi_Application_h

interface/src/Application_render.cpp

@@ -72,6 +72,12 @@ void Application::paintGL() {
     {
         QMutexLocker viewLocker(&_renderArgsMutex);
         renderArgs = _appRenderArgs._renderArgs;
+
+        // don't render if there is no context.
+        if (!_appRenderArgs._renderArgs._context) {
+            return;
+        }
+
         HMDSensorPose = _appRenderArgs._headPose;
         eyeToWorld = _appRenderArgs._eyeToWorld;
         sensorToWorld = _appRenderArgs._sensorToWorld;