void SDL_UnlockAudio(void)

void MyAudioCallback(void *userdata, Uint8* stream, int len)
{
    printf("The audio callback is running!\n");
    SDL_memset(stream, 0, len);  // just silence.
    printf("The audio callback is done!\n");
}

// don't lock for 2 seconds at a time in real life, please.
SDL_Delay(2000);  // callback runs for 2 seconds.
SDL_LockAudio();
printf("The audio callback can't be running right now!\n");
SDL_Delay(2000);  // callback doesn't run for 2 seconds.
printf("Ok, unlocking!\n");
SDL_UnlockAudio();
SDL_Delay(2000);  // callback runs for 2 seconds.

SDL_UnlockAudioDevice(1);