demonioImp.cpp

#include <iostream>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <cstdlib>
#include <cerrno>
#include <cstring>

using namespace std;

static void usage(const char *progname);

// crearSemaforo <keysem>
int
main(int argc, char *argv[]) {

  if (argc != 2) usage(argv[0]);

  int key = atoi(argv[1]);

  int semid = semget(key, 1, 0660);

  if (semid == -1) {
    cerr << "Error abriendo el semaforo: "
     << strerror(errno) << endl;
    return EXIT_FAILURE;
  }

  for (;;) {
    struct sembuf ops[1]; //  = { { 0, -1, 0} };

    // wait(sem)
    ops[0].sem_num = 0;
    ops[0].sem_op  = -1;
    ops[0].sem_flg = 0;
    cout << "Esperando por mensajes de impresion" << endl;
    semop(semid, ops, 1);
    cout << "Operacion recibida" << endl;
  }

  return EXIT_SUCCESS;
}

static void
usage(const char *progname) {
  cerr << "Uso: " << progname
       << " <semkey> " << endl;
  exit(EXIT_FAILURE);
}