QtUtils: add RunOnObject

Source/Core/DolphinQt2/QtUtils/RunOnObject.h

@@ -0,0 +1,34 @@
+// Copyright 2017 Dolphin Emulator Project
+// Licensed under GPLv2+
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <type_traits>
+#include <utility>
+
+#include "Common/Event.h"
+#include "DolphinQt2/QtUtils/QueueOnObject.h"
+
+class QObject;
+
+// QWidget and subclasses are not thread-safe! This helper takes arbitrary code from any thread,
+// safely runs it on the appropriate GUI thread, waits for it to finish, and returns the result.
+
+template <typename F>
+auto RunOnObject(QObject* object, F&& functor)
+{
+  // If we queue up a functor on the current thread, it won't run until we return to the event loop,
+  // which means waiting for it to finish will never complete. Instead, run it immediately.
+  if (object->thread() == QThread::currentThread())
+    return functor();
+
+  Common::Event event;
+  std::result_of_t<F()> result;
+  QueueOnObject(object, [&event, &result, functor = std::forward<F>(functor) ] {
+    result = functor();
+    event.Set();
+  });
+  event.Wait();
+  return result;
+}