al_unref_user_event - Allegro 5 API

       Decrease the reference count of a user-defined event.  This must be called on any user event that you get
       from  al_get_next_event(3alleg5), al_peek_next_event(3alleg5), al_wait_for_event(3alleg5), etc.  which is
       reference counted.  This function does nothing if the event is not reference counted.

       al_unref_user_event - Allegro 5 API

al_emit_user_event(3alleg5), ALLEGRO_USER_EVENT(3alleg5)

Allegro reference manual                                                            al_unref_user_event(3alleg5)

              #include <allegro5/allegro.h>

              void al_unref_user_event(ALLEGRO_USER_EVENT *event)