From d6b4c8e7dae6fad7c6fbd05722e4b7855970740c Mon Sep 17 00:00:00 2001
From: Cameron Gutman <aicommander@gmail.com>
Date: Sun, 20 Jan 2019 14:08:53 -0800
Subject: [PATCH] Avoid blocking decoding operations during Present calls

---
 app/streaming/video/ffmpeg-renderers/dxva2.cpp | 16 ++++++++++++++--
 app/streaming/video/ffmpeg-renderers/dxva2.h   |  1 +
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/app/streaming/video/ffmpeg-renderers/dxva2.cpp b/app/streaming/video/ffmpeg-renderers/dxva2.cpp
index 4584084a..5c2b8a4f 100644
--- a/app/streaming/video/ffmpeg-renderers/dxva2.cpp
+++ b/app/streaming/video/ffmpeg-renderers/dxva2.cpp
@@ -27,7 +27,8 @@ DXVA2Renderer::DXVA2Renderer() :
     m_ProcService(nullptr),
     m_Processor(nullptr),
     m_FrameIndex(0),
-    m_OverlayFont(nullptr)
+    m_OverlayFont(nullptr),
+    m_BlockingPresent(false)
 {
     RtlZeroMemory(m_DecSurfaces, sizeof(m_DecSurfaces));
     RtlZeroMemory(&m_DXVAContext, sizeof(m_DXVAContext));
@@ -541,6 +542,8 @@ bool DXVA2Renderer::initializeDevice(SDL_Window* window, bool enableVsync)
             d3dpp.BackBufferCount = 1;
         }
 
+        m_BlockingPresent = false;
+
         SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION,
                     "Windowed mode with DWM running");
     }
@@ -550,6 +553,7 @@ bool DXVA2Renderer::initializeDevice(SDL_Window* window, bool enableVsync)
         d3dpp.PresentationInterval = D3DPRESENT_INTERVAL_ONE;
         d3dpp.SwapEffect = D3DSWAPEFFECT_DISCARD;
         d3dpp.BackBufferCount = 1;
+        m_BlockingPresent = true;
 
         SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION,
                     "V-Sync enabled");
@@ -560,6 +564,7 @@ bool DXVA2Renderer::initializeDevice(SDL_Window* window, bool enableVsync)
         d3dpp.PresentationInterval = D3DPRESENT_INTERVAL_IMMEDIATE;
         d3dpp.SwapEffect = D3DSWAPEFFECT_DISCARD;
         d3dpp.BackBufferCount = 1;
+        m_BlockingPresent = false;
 
         SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION,
                     "V-Sync disabled in tearing mode");
@@ -872,7 +877,14 @@ void DXVA2Renderer::renderFrameAtVsync(AVFrame *frame)
         return;
     }
 
-    hr = m_Device->PresentEx(nullptr, nullptr, nullptr, nullptr, 0);
+    do {
+        // Use D3DPRESENT_DONOTWAIT if present may block in order to avoid holding the giant
+        // lock around this D3D device for excessive lengths of time (blocking concurrent decoding tasks).
+        hr = m_Device->PresentEx(nullptr, nullptr, nullptr, nullptr, m_BlockingPresent ? D3DPRESENT_DONOTWAIT : 0);
+        if (hr == D3DERR_WASSTILLDRAWING) {
+            SDL_Delay(1);
+        }
+    } while (hr == D3DERR_WASSTILLDRAWING);
     if (FAILED(hr)) {
         SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
                      "PresentEx() failed: %x",
diff --git a/app/streaming/video/ffmpeg-renderers/dxva2.h b/app/streaming/video/ffmpeg-renderers/dxva2.h
index a68ea9d1..a8070117 100644
--- a/app/streaming/video/ffmpeg-renderers/dxva2.h
+++ b/app/streaming/video/ffmpeg-renderers/dxva2.h
@@ -70,4 +70,5 @@ private:
     DXVA2_VideoDesc m_Desc;
     REFERENCE_TIME m_FrameIndex;
     LPD3DXFONT m_OverlayFont;
+    bool m_BlockingPresent;
 };