Add calls to XInitThreads() to allow driver multithreading optimisations

qrenderdoc/Code/qrenderdoc.cpp

@@ -52,6 +52,10 @@ void sharedLogOutput(QtMsgType type, const QMessageLogContext &context, const QS
 
 int main(int argc, char *argv[])
 {
+  // call this as the very first thing - no-op on other platforms, but on linux it means
+  // XInitThreads will be called allowing driver access to xlib on multiple threads.
+  QCoreApplication::setAttribute(Qt::AA_X11InitThreads);
+
   qInstallMessageHandler(sharedLogOutput);
 
   qInfo() << "QRenderDoc initialising.";

renderdoccmd/renderdoccmd_linux.cpp

@@ -210,6 +210,9 @@ void DisplayRendererPreview(IReplayController *renderer, TextureDisplay &display
   // need to create a hybrid setup xlib and xcb in case only one or the other is supported.
   // We'll prefer xcb
 
+  // call XInitThreads - although we don't use xlib concurrently the driver might need to.
+  XInitThreads();
+
   Display *display = XOpenDisplay(NULL);
 
   if(display == NULL)