Refactor Pacer to handle both blocking and non-blocking VsyncSources

app/streaming/video/ffmpeg-renderers/pacer/dxvsyncsource.cpp

@@ -6,17 +6,18 @@
 
 DxVsyncSource::DxVsyncSource(Pacer* pacer) :
     m_Pacer(pacer),
-    m_Thread(nullptr),
+    m_Gdi32Handle(nullptr),
-    m_Gdi32Handle(nullptr)
+    m_LastMonitor(nullptr)
 {
-    SDL_AtomicSet(&m_Stopping, 0);
+    SDL_zero(m_WaitForVblankEventParams);
 }
 
 DxVsyncSource::~DxVsyncSource()
 {
-    if (m_Thread != nullptr) {
+    if (m_WaitForVblankEventParams.hAdapter != 0) {
-        SDL_AtomicSet(&m_Stopping, 1);
+        D3DKMT_CLOSEADAPTER closeAdapterParams = {};
-        SDL_WaitThread(m_Thread, nullptr);
+        closeAdapterParams.hAdapter = m_WaitForVblankEventParams.hAdapter;
+        m_D3DKMTCloseAdapter(&closeAdapterParams);
     }
 
     if (m_Gdi32Handle != nullptr) {
@@ -24,10 +25,8 @@ DxVsyncSource::~DxVsyncSource()
     }
 }
 
-bool DxVsyncSource::initialize(SDL_Window* window, int displayFps)
+bool DxVsyncSource::initialize(SDL_Window* window, int)
 {
-    m_DisplayFps = displayFps;
-
     m_Gdi32Handle = LoadLibraryA("gdi32.dll");
     if (m_Gdi32Handle == nullptr) {
         SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
@@ -59,114 +58,89 @@ bool DxVsyncSource::initialize(SDL_Window* window, int displayFps)
         return false;
     }
 
-    m_Window = info.info.win.window;
+    // Pacer should only create us on Win32
+    SDL_assert(info.subsystem == SDL_SYSWM_WINDOWS);
 
-    m_Thread = SDL_CreateThread(vsyncThread, "DXVsync", this);
+    m_Window = info.info.win.window;
-    if (m_Thread == nullptr) {
-        SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
-                     "Unable to create DX V-sync thread: %s",
-                     SDL_GetError());
-        return false;
-    }
 
     return true;
 }
 
-int DxVsyncSource::vsyncThread(void* context)
+bool DxVsyncSource::isAsync()
 {
-    DxVsyncSource* me = reinterpret_cast<DxVsyncSource*>(context);
+    // We wait in the context of the Pacer thread
+    return false;
+}
 
-#if SDL_VERSION_ATLEAST(2, 0, 9)
+void DxVsyncSource::waitForVsync()
-    SDL_SetThreadPriority(SDL_THREAD_PRIORITY_TIME_CRITICAL);
+{
-#else
+    NTSTATUS status;
-    SDL_SetThreadPriority(SDL_THREAD_PRIORITY_HIGH);
-#endif
 
-    D3DKMT_OPENADAPTERFROMHDC openAdapterParams = {};
+    // If the monitor has changed from last time, open the new adapter
-    HMONITOR lastMonitor = nullptr;
+    HMONITOR currentMonitor = MonitorFromWindow(m_Window, MONITOR_DEFAULTTONEAREST);
-    DEVMODEA monitorMode;
+    if (currentMonitor != m_LastMonitor) {
-    monitorMode.dmSize = sizeof(monitorMode);
+        MONITORINFOEXA monitorInfo = {};
-
+        monitorInfo.cbSize = sizeof(monitorInfo);
-    while (SDL_AtomicGet(&me->m_Stopping) == 0) {
+        if (!GetMonitorInfoA(currentMonitor, &monitorInfo)) {
-        D3DKMT_WAITFORVERTICALBLANKEVENT waitForVblankEventParams;
+            SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
-        NTSTATUS status;
+                         "GetMonitorInfo() failed: %d",
-
+                         GetLastError());
-        // If the monitor has changed from last time, open the new adapter
+            return;
-        HMONITOR currentMonitor = MonitorFromWindow(me->m_Window, MONITOR_DEFAULTTONEAREST);
-        if (currentMonitor != lastMonitor) {
-            MONITORINFOEXA monitorInfo = {};
-            monitorInfo.cbSize = sizeof(monitorInfo);
-            if (!GetMonitorInfoA(currentMonitor, &monitorInfo)) {
-                SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
-                             "GetMonitorInfo() failed: %d",
-                             GetLastError());
-                SDL_Delay(10);
-                continue;
-            }
-
-            if (!EnumDisplaySettingsA(monitorInfo.szDevice, ENUM_CURRENT_SETTINGS, &monitorMode)) {
-                SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
-                             "EnumDisplaySettings() failed: %d",
-                             GetLastError());
-                SDL_Delay(10);
-                continue;
-            }
-
-            SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION,
-                        "Monitor changed: %s %d Hz",
-                        monitorInfo.szDevice,
-                        monitorMode.dmDisplayFrequency);
-
-            if (openAdapterParams.hAdapter != 0) {
-                D3DKMT_CLOSEADAPTER closeAdapterParams = {};
-                closeAdapterParams.hAdapter = openAdapterParams.hAdapter;
-                me->m_D3DKMTCloseAdapter(&closeAdapterParams);
-            }
-
-            openAdapterParams.hDc = CreateDCA(nullptr, monitorInfo.szDevice, nullptr, nullptr);
-            if (!openAdapterParams.hDc) {
-                SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
-                             "CreateDC() failed: %d",
-                             GetLastError());
-                SDL_Delay(10);
-                continue;
-            }
-
-            status = me->m_D3DKMTOpenAdapterFromHdc(&openAdapterParams);
-            DeleteDC(openAdapterParams.hDc);
-
-            if (status != STATUS_SUCCESS) {
-                SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
-                             "D3DKMTOpenAdapterFromHdc() failed: %x",
-                             status);
-                SDL_Delay(10);
-                continue;
-            }
-
-            lastMonitor = currentMonitor;
         }
 
-        waitForVblankEventParams.hAdapter = openAdapterParams.hAdapter;
+        DEVMODEA monitorMode;
-        waitForVblankEventParams.hDevice = 0;
+        monitorMode.dmSize = sizeof(monitorMode);
-        waitForVblankEventParams.VidPnSourceId = openAdapterParams.VidPnSourceId;
+        if (!EnumDisplaySettingsA(monitorInfo.szDevice, ENUM_CURRENT_SETTINGS, &monitorMode)) {
+            SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
+                         "EnumDisplaySettings() failed: %d",
+                         GetLastError());
+            return;
+        }
+
+        SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION,
+                    "Monitor changed: %s %d Hz",
+                    monitorInfo.szDevice,
+                    monitorMode.dmDisplayFrequency);
+
+        // Close the old adapter
+        if (m_WaitForVblankEventParams.hAdapter != 0) {
+            D3DKMT_CLOSEADAPTER closeAdapterParams = {};
+            closeAdapterParams.hAdapter = m_WaitForVblankEventParams.hAdapter;
+            m_D3DKMTCloseAdapter(&closeAdapterParams);
+        }
+
+        D3DKMT_OPENADAPTERFROMHDC openAdapterParams = {};
+        openAdapterParams.hDc = CreateDCA(nullptr, monitorInfo.szDevice, nullptr, nullptr);
+        if (!openAdapterParams.hDc) {
+            SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
+                         "CreateDC() failed: %d",
+                         GetLastError());
+            return;
+        }
+
+        // Open the new adapter
+        status = m_D3DKMTOpenAdapterFromHdc(&openAdapterParams);
+        DeleteDC(openAdapterParams.hDc);
 
-        status = me->m_D3DKMTWaitForVerticalBlankEvent(&waitForVblankEventParams);
         if (status != STATUS_SUCCESS) {
             SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
-                         "D3DKMTWaitForVerticalBlankEvent() failed: %x",
+                         "D3DKMTOpenAdapterFromHdc() failed: %x",
                          status);
-            SDL_Delay(10);
+            return;
-            continue;
         }
 
-        me->m_Pacer->vsyncCallback(1000 / me->m_DisplayFps);
+        m_WaitForVblankEventParams.hAdapter = openAdapterParams.hAdapter;
+        m_WaitForVblankEventParams.hDevice = 0;
+        m_WaitForVblankEventParams.VidPnSourceId = openAdapterParams.VidPnSourceId;
+
+        m_LastMonitor = currentMonitor;
     }
 
-    if (openAdapterParams.hAdapter != 0) {
+    status = m_D3DKMTWaitForVerticalBlankEvent(&m_WaitForVblankEventParams);
-        D3DKMT_CLOSEADAPTER closeAdapterParams = {};
+    if (status != STATUS_SUCCESS) {
-        closeAdapterParams.hAdapter = openAdapterParams.hAdapter;
+        SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
-        me->m_D3DKMTCloseAdapter(&closeAdapterParams);
+                     "D3DKMTWaitForVerticalBlankEvent() failed: %x",
+                     status);
+        return;
     }
-
-    return 0;
 }

app/streaming/video/ffmpeg-renderers/pacer/dxvsyncsource.h

@@ -35,17 +35,18 @@ public:
 
     virtual ~DxVsyncSource();
 
-    virtual bool initialize(SDL_Window* window, int displayFps);
+    virtual bool initialize(SDL_Window* window, int) override;
+
+    virtual bool isAsync() override;
+
+    virtual void waitForVsync() override;
 
 private:
-    static int vsyncThread(void* context);
-
     Pacer* m_Pacer;
-    SDL_Thread* m_Thread;
-    SDL_atomic_t m_Stopping;
     HMODULE m_Gdi32Handle;
     HWND m_Window;
-    int m_DisplayFps;
+    HMONITOR m_LastMonitor;
+    D3DKMT_WAITFORVERTICALBLANKEVENT m_WaitForVblankEventParams;
 
     PFND3DKMTOPENADAPTERFROMHDC m_D3DKMTOpenAdapterFromHdc;
     PFND3DKMTCLOSEADAPTER m_D3DKMTCloseAdapter;

app/streaming/video/ffmpeg-renderers/pacer/pacer.cpp

@@ -30,6 +30,7 @@
 
 Pacer::Pacer(IFFmpegRenderer* renderer, PVIDEO_STATS videoStats) :
     m_RenderThread(nullptr),
+    m_VsyncThread(nullptr),
     m_Stopping(false),
     m_VsyncSource(nullptr),
     m_VsyncRenderer(renderer),
@@ -42,12 +43,19 @@ Pacer::Pacer(IFFmpegRenderer* renderer, PVIDEO_STATS videoStats) :
 
 Pacer::~Pacer()
 {
+    m_Stopping = true;
+
+    // Stop the V-sync thread
+    if (m_VsyncThread != nullptr) {
+        m_VsyncSignalled.wakeAll();
+        SDL_WaitThread(m_VsyncThread, nullptr);
+    }
+
     // Stop V-sync callbacks
     delete m_VsyncSource;
     m_VsyncSource = nullptr;
 
     // Stop the render thread
-    m_Stopping = true;
     if (m_RenderThread != nullptr) {
         m_RenderQueueNotEmpty.wakeAll();
         SDL_WaitThread(m_RenderThread, nullptr);
@@ -89,6 +97,39 @@ void Pacer::renderOnMainThread()
     }
 }
 
+int Pacer::vsyncThread(void *context)
+{
+    Pacer* me = reinterpret_cast<Pacer*>(context);
+
+#if SDL_VERSION_ATLEAST(2, 0, 9)
+    SDL_SetThreadPriority(SDL_THREAD_PRIORITY_TIME_CRITICAL);
+#else
+    SDL_SetThreadPriority(SDL_THREAD_PRIORITY_HIGH);
+#endif
+
+    bool async = me->m_VsyncSource->isAsync();
+    while (!me->m_Stopping) {
+        if (async) {
+            // Wait for the VSync source to invoke signalVsync() or 100ms to elapse
+            me->m_FrameQueueLock.lock();
+            me->m_VsyncSignalled.wait(&me->m_FrameQueueLock, 100);
+            me->m_FrameQueueLock.unlock();
+        }
+        else {
+            // Let the VSync source wait in the context of our thread
+            me->m_VsyncSource->waitForVsync();
+        }
+
+        if (me->m_Stopping) {
+            break;
+        }
+
+        me->handleVsync(1000 / me->m_DisplayFps);
+    }
+
+    return 0;
+}
+
 int Pacer::renderThread(void* context)
 {
     Pacer* me = reinterpret_cast<Pacer*>(context);
@@ -153,7 +194,7 @@ void Pacer::enqueueFrameForRenderingAndUnlock(AVFrame *frame)
 
 // Called in an arbitrary thread by the IVsyncSource on V-sync
 // or an event synchronized with V-sync
-void Pacer::vsyncCallback(int timeUntilNextVsyncMillis)
+void Pacer::handleVsync(int timeUntilNextVsyncMillis)
 {
     // Make sure initialize() has been called
     SDL_assert(m_MaxVideoFps != 0);
@@ -217,7 +258,7 @@ bool Pacer::initialize(SDL_Window* window, int maxVideoFps, bool enablePacing)
 
     if (enablePacing) {
         SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION,
-                    "Frame pacing active: target %d Hz with %d FPS stream",
+                    "Frame pacing: target %d Hz with %d FPS stream",
                     m_DisplayFps, m_MaxVideoFps);
 
         SDL_SysWMinfo info;
@@ -255,7 +296,10 @@ bool Pacer::initialize(SDL_Window* window, int maxVideoFps, bool enablePacing)
         SDL_assert(m_VsyncSource != nullptr || !(m_RendererAttributes & RENDERER_ATTRIBUTE_FORCE_PACING));
 
         if (m_VsyncSource != nullptr && !m_VsyncSource->initialize(window, m_DisplayFps)) {
-            return false;
+            SDL_LogWarn(SDL_LOG_CATEGORY_APPLICATION,
+                        "Vsync source failed to initialize. Frame pacing will not be available!");
+            delete m_VsyncSource;
+            m_VsyncSource = nullptr;
         }
     }
     else {
@@ -264,6 +308,10 @@ bool Pacer::initialize(SDL_Window* window, int maxVideoFps, bool enablePacing)
                     m_DisplayFps, m_MaxVideoFps);
     }
 
+    if (m_VsyncSource != nullptr) {
+        m_VsyncThread = SDL_CreateThread(Pacer::vsyncThread, "PacerVsync", this);
+    }
+
     if (m_VsyncRenderer->isRenderThreadSupported()) {
         m_RenderThread = SDL_CreateThread(Pacer::renderThread, "PacerRender", this);
     }
@@ -271,6 +319,11 @@ bool Pacer::initialize(SDL_Window* window, int maxVideoFps, bool enablePacing)
     return true;
 }
 
+void Pacer::signalVsync()
+{
+    m_VsyncSignalled.wakeOne();
+}
+
 void Pacer::renderFrame(AVFrame* frame)
 {
     // Count time spent in Pacer's queues

app/streaming/video/ffmpeg-renderers/pacer/pacer.h

@@ -11,6 +11,15 @@ class IVsyncSource {
 public:
     virtual ~IVsyncSource() {}
     virtual bool initialize(SDL_Window* window, int displayFps) = 0;
+
+    // Asynchronous sources produce callbacks on their own, while synchronous
+    // sources require calls to waitForVsync().
+    virtual bool isAsync() = 0;
+
+    virtual void waitForVsync() {
+        // Synchronous sources must implement waitForVsync()!
+        SDL_assert(false);
+    }
 };
 
 class Pacer
@@ -24,13 +33,17 @@ public:
 
     bool initialize(SDL_Window* window, int maxVideoFps, bool enablePacing);
 
-    void vsyncCallback(int timeUntilNextVsyncMillis);
+    void signalVsync();
 
     void renderOnMainThread();
 
 private:
+    static int vsyncThread(void* context);
+
     static int renderThread(void* context);
 
+    void handleVsync(int timeUntilNextVsyncMillis);
+
     void enqueueFrameForRenderingAndUnlock(AVFrame* frame);
 
     void renderFrame(AVFrame* frame);
@@ -44,7 +57,9 @@ private:
     QMutex m_FrameQueueLock;
     QWaitCondition m_RenderQueueNotEmpty;
     QWaitCondition m_PacingQueueNotEmpty;
+    QWaitCondition m_VsyncSignalled;
     SDL_Thread* m_RenderThread;
+    SDL_Thread* m_VsyncThread;
     bool m_Stopping;
 
     IVsyncSource* m_VsyncSource;

app/streaming/video/ffmpeg-renderers/pacer/waylandvsyncsource.cpp

@@ -10,8 +10,7 @@ WaylandVsyncSource::WaylandVsyncSource(Pacer* pacer)
     : m_Pacer(pacer),
       m_Display(nullptr),
       m_Surface(nullptr),
-      m_Callback(nullptr),
+      m_Callback(nullptr)
-      m_LastFrameTime(0)
 {
 
 }
@@ -24,7 +23,7 @@ WaylandVsyncSource::~WaylandVsyncSource()
     }
 }
 
-bool WaylandVsyncSource::initialize(SDL_Window* window, int displayFps)
+bool WaylandVsyncSource::initialize(SDL_Window* window, int)
 {
     SDL_SysWMinfo info;
 
@@ -40,7 +39,6 @@ bool WaylandVsyncSource::initialize(SDL_Window* window, int displayFps)
     // Pacer shoud not create us for non-Wayland windows
     SDL_assert(info.subsystem == SDL_SYSWM_WAYLAND);
 
-    m_DisplayFps = displayFps;
     m_Display = info.info.wl.display;
     m_Surface = info.info.wl.surface;
 
@@ -52,7 +50,13 @@ bool WaylandVsyncSource::initialize(SDL_Window* window, int displayFps)
     return true;
 }
 
-void WaylandVsyncSource::frameDone(void* data, struct wl_callback* oldCb, uint32_t time)
+bool WaylandVsyncSource::isAsync()
+{
+    // Wayland frame callbacks are asynchronous
+    return true;
+}
+
+void WaylandVsyncSource::frameDone(void* data, struct wl_callback* oldCb, uint32_t)
 {
     auto me = (WaylandVsyncSource*)data;
 
@@ -60,18 +64,12 @@ void WaylandVsyncSource::frameDone(void* data, struct wl_callback* oldCb, uint32
     SDL_assert(oldCb == me->m_Callback);
     wl_callback_destroy(oldCb);
 
-    // Register for another callback before invoking Pacer to ensure we don't miss
+    // Wake the Pacer Vsync thread
-    // a frame callback if Pacer takes too long.
+    me->m_Pacer->signalVsync();
+
+    // Register for another callback
     me->m_Callback = wl_surface_frame(me->m_Surface);
     wl_callback_add_listener(me->m_Callback, &s_FrameListener, data);
     wl_surface_commit(me->m_Surface);
     wl_display_flush(me->m_Display);
-
-    if (me->m_LastFrameTime != 0) {
-        // Assuming that the time until the next V-Sync will usually be equal to the
-        // time from last callback to this one but cap it at 2x the expected frame period.
-        me->m_Pacer->vsyncCallback(SDL_min(time - me->m_LastFrameTime, 2000 / me->m_DisplayFps));
-    }
-
-    me->m_LastFrameTime = time;
 }

app/streaming/video/ffmpeg-renderers/pacer/waylandvsyncsource.h

@@ -12,7 +12,9 @@ public:
 
     virtual ~WaylandVsyncSource();
 
-    virtual bool initialize(SDL_Window* window, int displayFps);
+    virtual bool initialize(SDL_Window* window, int displayFps) override;
+
+    virtual bool isAsync() override;
 
 private:
     static void frameDone(void* data, struct wl_callback* oldCb, uint32_t time);
@@ -20,10 +22,8 @@ private:
     static const struct wl_callback_listener s_FrameListener;
 
     Pacer* m_Pacer;
-    int m_DisplayFps;
     wl_display* m_Display;
     wl_surface* m_Surface;
     wl_callback* m_Callback;
-    uint32_t m_LastFrameTime;
 };