ejercicio 10 Semaforo

#include <sys/shm.h>
#include <unistd.h>
#include <sys/stat.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <wait.h>
#include <fcntl.h>
#include<sys/ipc.h>
#include <sys/sem.h>
#include <string.h>

void P(int semid, int nsem)
{
	struct sembuf buf;
	buf.sem_num = nsem;
	buf.sem_op  = -1;
	buf.sem_flg = 0;
	semop(semid,&buf,1);
}

void V(int semid, int nsem)
{
	struct sembuf buf;
	buf.sem_num = nsem;
	buf.sem_op  = 1;
	buf.sem_flg = 0;
	semop(semid,&buf,1);
}

int crea_shm(key_t Clave, int cantby)
{
	int shmid;
	shmid = shmget(Clave,cantby,IPC_CREAT | 0777);
	return shmid;
}

int crea_sem(key_t Clave, int cantsem)
{
	int semid ;
	semid = semget(Clave,cantsem,IPC_CREAT | 0777);
	return semid;
}

int init_sem(int semid,int nsem,int valor)
{
	int status;
	status = semctl(semid, nsem, SETVAL, valor);
	return status;
}

main(int argc,char **argv)
{
	int semid;
	int nsem = 2;
	int aux = 0;
	int maxNum;
	int pid1, pid2;
	int valor = 0;
	int status;
	key_t Clave;

	printf("Ingrese el valor maximo: ");
	scanf("%d",&maxNum);
	semid = crea_sem(Clave,nsem);
	printf("%d\n", semid);
	if (semid == -1)
		perror("error semget\n")
	else
		perror("\n");
	status = init_sem(semid, 0, 1);
	status = init_sem(semid, 1, 0);
	if (status == -1)
		perror("error semctl\n")
	else
		perror("\n");


	Clave = ftok ("/bin/ls", 33);
        if (Clave == -1)
        {
                    printf("Error, no se consigue la clave\n");
                    exit(EXIT_FAILURE);
            }

            printf("fin primera etapa\n");
            pid1 = fork();

            if(pid1 == -1)
            {
                    printf("ERROR\n");
                    exit(EXIT_FAILURE);
            }

            if (pid1 == 0)
            {
                    aux++;
                    while (aux <= maxNum)
                    {
                            P(semid, 0);
                            aux++;
                            if (aux <= maxNum)
                                            printf("%d\n", aux);
                            aux++;
                            V(semid, 1);

                    }

                    exit(EXIT_SUCCESS);
            }
            else
            {
                    pid2 = fork();
                    if(pid2 == -1)
                    {
                            printf("ERROR\n");
                            exit(EXIT_FAILURE);
                    }

                    if (pid2 == 0)
                    {
                            while (aux <= maxNum)
                            {
                                    P(semid, 1);
                                    aux++;
                                    if (aux <= maxNum)
                                            printf("%d\n", aux);
                                    aux++;
                                    V(semid, 0);
                            }
                    }
                    exit(EXIT_SUCCESS);
            }
            exit(EXIT_SUCCESS);
    }