From e5559fa865473af6d550253167ba1358877dd4c7 Mon Sep 17 00:00:00 2001
From: Brad Davis <bdavis@saintandreas.org>
Date: Wed, 31 Jan 2018 10:38:20 -0800
Subject: [PATCH] Better fix for AMD crashing (hopefully

---
 libraries/ui/src/ui/OffscreenQmlSurface.cpp | 39 ++++++++++++++-------
 libraries/ui/src/ui/OffscreenQmlSurface.h   |  4 +++
 2 files changed, 31 insertions(+), 12 deletions(-)

diff --git a/libraries/ui/src/ui/OffscreenQmlSurface.cpp b/libraries/ui/src/ui/OffscreenQmlSurface.cpp
index 902f91f9b8..d39b8a2678 100644
--- a/libraries/ui/src/ui/OffscreenQmlSurface.cpp
+++ b/libraries/ui/src/ui/OffscreenQmlSurface.cpp
@@ -565,14 +565,18 @@ void OffscreenQmlSurface::render() {
 
     {
         // If the most recent texture was unused, we can directly recycle it
-        if (_latestTextureAndFence.first) {
-            offscreenTextures.releaseTexture(_latestTextureAndFence);
-            _latestTextureAndFence = { 0, 0 };
-        }
-
-        _latestTextureAndFence = { texture, glFenceSync(GL_SYNC_GPU_COMMANDS_COMPLETE, 0) };
+        auto fence = glFenceSync(GL_SYNC_GPU_COMMANDS_COMPLETE, 0);
         // Fence will be used in another thread / context, so a flush is required
         glFlush();
+
+        {
+            Lock lock(_latestTextureAndFenceMutex);
+            if (_latestTextureAndFence.first) {
+                offscreenTextures.releaseTexture(_latestTextureAndFence);
+                _latestTextureAndFence = { 0, 0 };
+            }
+            _latestTextureAndFence = { texture, fence};
+        }
     }
 
     _quickWindow->resetOpenGLState();
@@ -583,13 +587,21 @@ void OffscreenQmlSurface::render() {
 bool OffscreenQmlSurface::fetchTexture(TextureAndFence& textureAndFence) {
     textureAndFence = { 0, 0 };
 
+    // Lock free early check
     if (0 == _latestTextureAndFence.first) {
         return false;
     }
 
     // Ensure writes to the latest texture are complete before before returning it for reading
-    textureAndFence = _latestTextureAndFence;
-    _latestTextureAndFence = { 0, 0 };
+    {
+        Lock lock(_latestTextureAndFenceMutex);
+        // Double check inside the lock
+        if (0 == _latestTextureAndFence.first) {
+            return false;
+        }
+        textureAndFence = _latestTextureAndFence;
+        _latestTextureAndFence = { 0, 0 };
+    }
     return true;
 }
 
@@ -797,10 +809,13 @@ void OffscreenQmlSurface::resize(const QSize& newSize_, bool forceResize) {
 
         // Release hold on the textures of the old size
         if (uvec2() != _size) {
-            // If the most recent texture was unused, we can directly recycle it
-            if (_latestTextureAndFence.first) {
-                offscreenTextures.releaseTexture(_latestTextureAndFence);
-                _latestTextureAndFence = { 0, 0 };
+            {
+                Lock lock(_latestTextureAndFenceMutex);
+                // If the most recent texture was unused, we can directly recycle it
+                if (_latestTextureAndFence.first) {
+                    offscreenTextures.releaseTexture(_latestTextureAndFence);
+                    _latestTextureAndFence = { 0, 0 };
+                }
             }
             offscreenTextures.releaseSize(_size);
         }
diff --git a/libraries/ui/src/ui/OffscreenQmlSurface.h b/libraries/ui/src/ui/OffscreenQmlSurface.h
index 4251bb6a9d..e50b07deee 100644
--- a/libraries/ui/src/ui/OffscreenQmlSurface.h
+++ b/libraries/ui/src/ui/OffscreenQmlSurface.h
@@ -167,6 +167,9 @@ public slots:
     bool handlePointerEvent(const PointerEvent& event, class QTouchDevice& device, bool release = false);
 
 private:
+    using Mutex = std::mutex;
+    using Lock = std::unique_lock<std::mutex>;
+
     QQuickWindow* _quickWindow { nullptr };
     QMyQuickRenderControl* _renderControl{ nullptr };
     QQmlContext* _qmlContext { nullptr };
@@ -185,6 +188,7 @@ private:
 #endif
     
     // Texture management
+    Mutex _latestTextureAndFenceMutex;
     TextureAndFence _latestTextureAndFence { 0, 0 };
 
     bool _render { false };