al_drain_audio_stream - Allegro 5 API

       You  should  call  this  to  finalise an audio stream that you will no longer be feeding, to wait for all
       pending buffers to finish playing.  The stream’s playing state will change to false.

       al_drain_audio_stream - Allegro 5 API

al_destroy_audio_stream(3alleg5)

Allegro reference manual                                                          al_drain_audio_stream(3alleg5)

              #include <allegro5/allegro_audio.h>

              void al_drain_audio_stream(ALLEGRO_AUDIO_STREAM *stream)