al_broadcast_cond man page
al_broadcast_cond — Allegro 5 API
#include <allegro5/allegro.h> void al_broadcast_cond(ALLEGRO_COND *cond)
Unblock all threads currently waiting on a condition variable. That is, broadcast that some condition which those threads were waiting for has become true.
Note: The pthreads spec says to lock the mutex associated with
condbefore signalling for predictable scheduling behaviour.