Some refactoring in multithreading.

src/GLBucket.cpp

@@ -0,0 +1,16 @@
+#include "GLBucket.h"
+
+#include <iostream>
+
+std::unique_ptr<GLBucket> GLBucket::s_instance = std::unique_ptr<GLBucket>(new GLBucket);
+
+GLBucket &GLBucket::instance()
+{
+    return *s_instance.get();
+}
+
+void GLBucket::runGlCall(const std::function<void(void)> &f)
+{
+    std::lock_guard<std::mutex> lock(m_mutex);
+    f();
+}