Wake up main thread immediately after new frame is pushed

app/app.pro

@@ -126,7 +126,8 @@ SOURCES += \
     path.cpp \
     settings/mappingmanager.cpp \
     gui/sdlgamepadkeynavigation.cpp \
-    streaming/video/overlaymanager.cpp
+    streaming/video/overlaymanager.cpp \
+    streaming/sdlhelper.cpp
 
 HEADERS += \
     utils.h \
@@ -153,7 +154,8 @@ HEADERS += \
     path.h \
     settings/mappingmanager.h \
     gui/sdlgamepadkeynavigation.h \
-    streaming/video/overlaymanager.h
+    streaming/video/overlaymanager.h \
+    streaming/sdlhelper.h
 
 # Platform-specific renderers and decoders
 ffmpeg {

app/streaming/sdlhelper.cpp

@@ -0,0 +1,45 @@
+#include "sdlhelper.h"
+
+SDL_cond* SDLHelper::s_EventCond;
+SDL_mutex* SDLHelper::s_EventMutex;
+
+void SDLHelper::initializeIfNeeded()
+{
+    if (!s_EventCond) {
+        s_EventCond = SDL_CreateCond();
+    }
+    if (!s_EventMutex) {
+        s_EventMutex = SDL_CreateMutex();
+    }
+}
+
+void SDLHelper::waitEvent(SDL_Event* event)
+{
+    initializeIfNeeded();
+
+    // We explicitly use SDL_PollEvent() and SDL_Delay() because
+    // SDL_WaitEventTimeout() has an internal SDL_Delay(10) inside which
+    // blocks this thread too long for high polling rate mice and high
+    // refresh rate displays.
+    while (!SDL_PollEvent(event)) {
+        // Sleep for up to 1 ms or until we are woken up by
+        // SDLHelper::pushEvent().
+        // FIXME: SDL should do this internally
+        SDL_LockMutex(s_EventMutex);
+        SDL_CondWaitTimeout(s_EventCond, s_EventMutex, 1);
+        SDL_UnlockMutex(s_EventMutex);
+        continue;
+    }
+}
+
+void SDLHelper::pushEvent(SDL_Event* event)
+{
+    initializeIfNeeded();
+
+    SDL_PushEvent(event);
+
+    // Immediately wake up the other waiting thread
+    SDL_LockMutex(s_EventMutex);
+    SDL_CondSignal(s_EventCond);
+    SDL_UnlockMutex(s_EventMutex);
+}

app/streaming/sdlhelper.h

@@ -0,0 +1,16 @@
+#pragma once
+
+#include <SDL.h>
+
+class SDLHelper
+{
+public:
+    static void waitEvent(SDL_Event* event);
+    static void pushEvent(SDL_Event* event);
+
+private:
+    static void initializeIfNeeded();
+
+    static SDL_cond* s_EventCond;
+    static SDL_mutex* s_EventMutex;
+};

app/streaming/session.cpp

@@ -1,6 +1,7 @@
 #include "session.h"
 #include "settings/streamingpreferences.h"
 #include "streaming/streamutils.h"
+#include "streaming/sdlhelper.h"
 
 #include <Limelight.h>
 #include <SDL.h>
@@ -981,14 +982,8 @@ void Session::exec(int displayOriginX, int displayOriginY)
     // because we want to suspend all Qt processing until the stream is over.
     SDL_Event event;
     for (;;) {
-        // We explicitly use SDL_PollEvent() and SDL_Delay() because
+        SDLHelper::waitEvent(&event);
-        // SDL_WaitEvent() has an internal SDL_Delay(10) inside which
+
-        // blocks this thread too long for high polling rate mice and high
-        // refresh rate displays.
-        if (!SDL_PollEvent(&event)) {
-            SDL_Delay(1);
-            continue;
-        }
         switch (event.type) {
         case SDL_QUIT:
             SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION,

app/streaming/video/decoder.h

@@ -3,6 +3,7 @@
 #include <Limelight.h>
 #include <SDL.h>
 #include "settings/streamingpreferences.h"
+#include "streaming/sdlhelper.h"
 
 #define SDL_CODE_FRAME_READY 0
 
@@ -53,6 +54,6 @@ public:
         event.user.data1 = data1;
         event.user.data2 = data2;
 
-        SDL_PushEvent(&event);
+        SDLHelper::pushEvent(&event);
     }
 };