Sets our main struct and passes it to the parent class.
Get the main Gtk struct
the main Gtk struct as a void*
Function to be called when starting a critical initialization section. The argument @location must point to a static 0-initialized variable that will be set to a value other than 0 at the end of the initialization section. In combination with g_once_init_leave() and the unique address @value_location, it can be ensured that an initialization section will be executed only once during a program's life time, and that concurrent threads are blocked until initialization completed. To be used in constructs like this:
Counterpart to g_once_init_enter(). Expects a location of a static 0-initialized initialization variable, and an initialization value other than 0. Sets the variable to the initialization value, and releases concurrent threads blocking in g_once_init_enter() on this initialization variable.
A #GOnce struct controls a one-time initialization function. Any one-time initialization function must have its own unique #GOnce struct.