al_wait_for_vsync - Allegro 5 API

       Wait  for  the beginning of a vertical retrace.  Some driver/card/monitor combinations may not be capable
       of this.

       Note how al_flip_display(3alleg5) usually already waits for the vertical retrace, so unless you are doing
       something special, there is no reason to call this function.

       Returns false if not possible, true if successful.

       al_wait_for_vsync - Allegro 5 API

al_flip_display(3alleg5)

Allegro reference manual                                                              al_wait_for_vsync(3alleg5)

              #include <allegro5/allegro.h>

              bool al_wait_for_vsync(void)