Fix XCB out-of-sequence abort after switching to non-threaded Qt renderer

app/backend/systemproperties.cpp

@@ -91,7 +91,36 @@ QRect SystemProperties::getNativeResolution(int displayIndex)
     return monitorNativeResolutions.value(displayIndex);
 }
 
+class QuerySdlVideoThread : public QThread
+{
+public:
+    QuerySdlVideoThread(SystemProperties* me) :
+        QThread(nullptr),
+        m_Me(me) {}
+
+    void run() override
+    {
+        m_Me->querySdlVideoInfoInternal();
+    }
+
+    SystemProperties* m_Me;
+};
+
 void SystemProperties::querySdlVideoInfo()
+{
+    if (WMUtils::isRunningX11() || WMUtils::isRunningWayland()) {
+        // Use a separate thread to temporarily initialize SDL
+        // video to avoid stomping on Qt's X11 and OGL state.
+        QuerySdlVideoThread thread(this);
+        thread.start();
+        thread.wait();
+    }
+    else {
+        querySdlVideoInfoInternal();
+    }
+}
+
+void SystemProperties::querySdlVideoInfoInternal()
 {
     hasHardwareAcceleration = false;
 
@@ -103,7 +132,8 @@ void SystemProperties::querySdlVideoInfo()
     }
 
     // Update display related attributes (max FPS, native resolution, etc).
-    refreshDisplays();
+    // We call the internal variant because we're already in a safe thread context.
+    refreshDisplaysInternal();
 
     SDL_Window* testWindow = SDL_CreateWindow("", 0, 0, 1280, 720,
                                               SDL_WINDOW_HIDDEN | StreamUtils::getPlatformWindowFlags());
@@ -129,7 +159,36 @@ void SystemProperties::querySdlVideoInfo()
     SDL_QuitSubSystem(SDL_INIT_VIDEO);
 }
 
+class RefreshDisplaysThread : public QThread
+{
+public:
+    RefreshDisplaysThread(SystemProperties* me) :
+        QThread(nullptr),
+        m_Me(me) {}
+
+    void run() override
+    {
+        m_Me->refreshDisplaysInternal();
+    }
+
+    SystemProperties* m_Me;
+};
+
 void SystemProperties::refreshDisplays()
+{
+    if (WMUtils::isRunningX11() || WMUtils::isRunningWayland()) {
+        // Use a separate thread to temporarily initialize SDL
+        // video to avoid stomping on Qt's X11 and OGL state.
+        RefreshDisplaysThread thread(this);
+        thread.start();
+        thread.wait();
+    }
+    else {
+        refreshDisplaysInternal();
+    }
+}
+
+void SystemProperties::refreshDisplaysInternal()
 {
     if (SDL_InitSubSystem(SDL_INIT_VIDEO) != 0) {
         SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,

app/backend/systemproperties.h

@@ -7,6 +7,9 @@ class SystemProperties : public QObject
 {
     Q_OBJECT
 
+    friend class QuerySdlVideoThread;
+    friend class RefreshDisplaysThread;
+
 public:
     SystemProperties();
 
@@ -33,6 +36,8 @@ signals:
 
 private:
     void querySdlVideoInfo();
+    void querySdlVideoInfoInternal();
+    void refreshDisplaysInternal();
 
     bool hasHardwareAcceleration;
     bool rendererAlwaysFullScreen;