Semaphore not working

[ovnyx]

Hello everyone,
i was trying to sincronize 2 non child procceses with a binary semaphore and it is working but, for some reason it is not blocking the CS.

when i execute the emisor script, it creates the semaphore and, a thread its created and i block with wait, and post the fragment of code i want, i checked with getvalue, and in the receptor script, i tried with O_CREAT | O_EXCL to verify if the semaphore its busy, and yeah, but i dont know why its not blocking, any ideas guys?

this are my codes:

/*

ping.c

*/


#include <stdio.h>
#include <pthread.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <semaphore.h>
#include <fcntl.h>
#include <sys/stat.h>


#define SNAME "/sem"
int value;
sem_t *semaphore;
//pthread_t thread;


int size(char *string){
      int counter = 1, string_size = 0;
      while (counter) {
            if (string[string_size] != NULL)
                  string_size++;
            else
                  counter = 0;
      }
      return string_size;
}


void *play(void *index){      //recibe el indice del hilo
      char *text = "PING";
      printf("valor del semaforo fuera de  la S.C: %d\n", value);


      sem_wait(&semaphore);
            printf("valor del semaforo dentroe la S.C: %d\n", value);
            for (size_t i = 0; i < size(text); i++){
                  printf("%c\n", text[i]);
                  sleep(2);
            }
      sem_post(&semaphore);
}


int main(int argc, char *argv[]) {
      semaphore = sem_open(SNAME, O_CREAT, 0666, 1);
      sem_getvalue(semaphore, &value);
      if (semaphore == -1) {
            perror("ERROR EN SEMAFORO");
            exit(-1);
      }


      //while(1){
            pthread_t thread;
            pthread_create(&thread, NULL, play, NULL);
            pthread_join(thread, NULL);
            printf("\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n");
      //}
      sem_close(semaphore);
      sem_unlink(SNAME);
      return 0;
}

/*

pong.c

*/

#include <sys/ipc.h>
#include <sys/types.h>
#include <sys/msg.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>


#define KEY 666
#define TAM_BUFFER 256




/*Cada posicion de la cola de mensajes sera una estructura
Puede contener lo que sea (cualquier tipo de variables)*/


typedef struct{
      long i;
      char msg[TAM_BUFFER];


}mensaje;


int main(int argc, char *argv[]) {
      int id_cola_mensajes, e_cola_mensajes, long_msg;      //id, error, tamano
      id_cola_mensajes = msgget(KEY, 0660 | IPC_CREAT);  //Crea la cola de mensaje y retorna el identificador de la misma


      if (id_cola_mensajes == -1) {
            perror("Error ID_COLA_MENSAJES");
            exit(-1);
      }


      int counter = 0;
      while(counter < 5){
            mensaje saludo;
            e_cola_mensajes = msgrcv(id_cola_mensajes, &saludo, TAM_BUFFER, 0, 0);


            if (e_cola_mensajes == -1) {
                  perror("Error msgrcv");
                  exit(-1);
            }


            printf("El mensaje es: %s\n", saludo.msg);
            counter++;
      }


      msgctl(id_cola_mensajes, IPC_RMID, NULL);  
      return 0;
}

I would appreciate any help

thanks in advice,
bless

[ddutch]

I have experience with mutex-es and never experienced any problems.
I can not really judge your application but isn't it a clearer way to use a mutex instead of a semaphore ?

Something like:

        while(pthread_mutex_trylock(&getCurrentThread_mutex));

           if(currentThread >= 0)
               ++currentThread;
        pthread_mutex_unlock(&getCurrentThread_mutex);

[ddutch]

Oops, sorry, I did not see that you deal with 2 separate processes. In that case a mutex can not be used.