#include <semaphore.h>
#include <sys/shm.h>

#define MAX 1000

struct fila
{
	char v[MAX];
	int head, tail;
	sem_t full, empty, mutex;
};

/************************ Buffer circular ************************/
void init(struct fila *f) {
	f->head = 0;
	f->tail = 0;
}

void add(struct fila *f, char c) {
	f->v[f->head] = c;
	f->head++;
	
	if(f->head >= MAX) f->head = 0;
}

char delete(struct fila *f) {
	char c = f->v[f->tail];
	f->tail++;
	
	if(f->tail >= MAX) f->tail = 0;
	
	return c;
}

/***************************** Fila *****************************/

struct fila *criar_fila() {
	struct fila *f;

	int id = shmget(IPC_PRIVATE, sizeof(struct fila), IPC_CREAT|0660);
	if(id < 0) { perror("shmget falhou."); exit(1); }

	f = shmat(id, NULL, 0);
	if(f < 0) { perror("shmat falhou."); exit(1); }

	sem_init(&f->mutex, 1, 1);
	sem_init(&f->empty, 1, 0);
	sem_init(&f->full, 1, MAX);

	init(f);

	return f;
}

char tirar_fila(struct fila *f) {
	sem_wait(&f->empty);
	sem_wait(&f->mutex);

	char c = delete(f);

	sem_post(&f->mutex);
	sem_post(&f->full);

	return c;
}

void por_fila(struct fila *f, char elem) {
	sem_wait(&f->full);
	sem_wait(&f->mutex);

	add(f, elem);

	sem_post(&f->mutex);
	sem_post(&f->empty);
}