From 84dc15aff62408bff63543f132282dbcc6426e51 Mon Sep 17 00:00:00 2001
From: Brad Davis <bdavis@saintandreas.org>
Date: Wed, 23 Mar 2016 12:06:52 -0700
Subject: [PATCH] Fix potential deadlock in QML

---
 libraries/gl/src/gl/OffscreenQmlSurface.cpp | 34 +++++++++++++++------
 libraries/shared/src/Finally.h              |  4 +++
 2 files changed, 29 insertions(+), 9 deletions(-)

diff --git a/libraries/gl/src/gl/OffscreenQmlSurface.cpp b/libraries/gl/src/gl/OffscreenQmlSurface.cpp
index d3699b54e6..e224adad07 100644
--- a/libraries/gl/src/gl/OffscreenQmlSurface.cpp
+++ b/libraries/gl/src/gl/OffscreenQmlSurface.cpp
@@ -23,6 +23,7 @@
 #include <PerfStat.h>
 #include <DependencyManager.h>
 #include <NumericalConstants.h>
+#include <Finally.h>
 
 #include "OffscreenGLCanvas.h"
 #include "GLEscrow.h"
@@ -84,6 +85,7 @@ protected:
     Queue _queue;
     QMutex _mutex;
     QWaitCondition _waitCondition;
+    std::atomic<bool> _rendering { false };
 
 private:
     // Event-driven methods
@@ -271,15 +273,25 @@ void OffscreenQmlRenderThread::resize() {
 }
 
 void OffscreenQmlRenderThread::render() {
-    if (_surface->_paused) {
+    // Ensure we always release the main thread
+    Finally releaseMainThread([this] {
         _waitCondition.wakeOne();
+    });
+
+    if (_surface->_paused) {
         return;
     }
 
-    QMutexLocker locker(&_mutex);
-    _renderControl->sync();
-    _waitCondition.wakeOne();
-    locker.unlock();
+    _rendering = true;
+    Finally unmarkRenderingFlag([this] {
+        _rendering = false;
+    });
+
+    {
+        QMutexLocker locker(&_mutex);
+        _renderControl->sync();
+        releaseMainThread.trigger();
+    }
 
     using namespace oglplus;
 
@@ -292,6 +304,7 @@ void OffscreenQmlRenderThread::render() {
         _fbo->AttachTexture(Framebuffer::Target::Draw, FramebufferAttachment::Color, *texture, 0);
         _fbo->Complete(Framebuffer::Target::Draw);
         {
+            PROFILE_RANGE("qml_render->rendercontrol")
             _renderControl->render();
             // FIXME The web browsers seem to be leaving GL in an error state.
             // Need a debug context with sync logging to figure out why.
@@ -380,8 +393,6 @@ void OffscreenQmlSurface::resize(const QSize& newSize_) {
                 std::max(static_cast<int>(scale * newSize.height()), 10));
     }
 
-
-
     QSize currentSize = _renderer->_quickWindow->geometry().size();
     if (newSize == currentSize) {
         return;
@@ -492,7 +503,12 @@ QObject* OffscreenQmlSurface::finishQmlLoad(std::function<void(QQmlContext*, QOb
 }
 
 void OffscreenQmlSurface::updateQuick() {
-    if (!_renderer || !_renderer->allowNewFrame(_maxFps)) {
+    // If we're 
+    //   a) not set up
+    //   b) already rendering a frame
+    //   c) rendering too fast
+    // then skip this 
+    if (!_renderer || _renderer->_rendering || !_renderer->allowNewFrame(_maxFps)) {
         return;
     }
 
@@ -502,11 +518,11 @@ void OffscreenQmlSurface::updateQuick() {
     }
 
     if (_render) {
+        PROFILE_RANGE(__FUNCTION__);
         // Lock the GUI size while syncing
         QMutexLocker locker(&(_renderer->_mutex));
         _renderer->_queue.add(RENDER);
         _renderer->_waitCondition.wait(&(_renderer->_mutex));
-
         _render = false;
     }
 
diff --git a/libraries/shared/src/Finally.h b/libraries/shared/src/Finally.h
index 59e8be0228..9070d49647 100644
--- a/libraries/shared/src/Finally.h
+++ b/libraries/shared/src/Finally.h
@@ -20,6 +20,10 @@ public:
     template <typename F>
     Finally(F f) : _f(f) {}
     ~Finally() { _f(); }
+    void trigger() {
+        _f();
+        _f = [] {};
+    }
 private:
     std::function<void()> _f;
 };