Explication a propos d'un programme semaphore please

**menzeli** · 24/03/2007, 19h35

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pv.h
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <errno.h>
 
extern int errno;
 
#define SEMPERM 0600
#define TRUE 1
#define FALSE 0
#define SEMKEY 0*200
#define SEMKEYSTR "0*200"
 
 
union _semun{
 int val;
 struct semid_ds *stat;
 unsigned short *array;
} 
 
int p (int semid);
int v (int semid);
int initsem (key_t semkey);
void handlesem (key_t semkey);
 
***********************
/* initsem.c -- semaphore initialisation */
 
#include "pv.h"
 
int initsem(key_t semkey)
{
    int status = 0, semid;
    union semun arg;
    arg.val = 1;
 
    if((semid = semget(semkey, 1, SEMPERM|IPC_CREAT|IPC_EXCL)) == -1)
    {
	if (errno ==EEXIST)
	    semid = semget(semkey, 1, 0);
    }
    else /* if created ... */
    {
	status = semctl(semid, 0, SETVAL, arg);
    }
 
    if (semid == -1 || status == -1)
    {
	perror("initsem failed");
	return(-1);
    }
 
    /* all okay */
    else
    return(semid);
}
void removesem (char *key)
{
    execlp ("ipcrm", "ipcrm", "-S", key,(char *) 0);
 
*************************
pc.c
#include "pv.h"
int p(int semid){
    struct sembuf p_buf;
 
    p_buf.sem_num = 0;
    p_buf.sem_op = -1;
    p_buf.sem_flg = SEM_UNDO; /* undoes operation if process exits! */
 
    if (semop(semid, &p_buf, 1) == -1)
    {
	perror("p(semid) failed");
	exit(1);
    } 
else
	return (0);
}
//p()
 
***************************
vc.c
#include "pv.h"
int v(int semid){
    struct sembuf v_buf;
 
    v_buf.sem_num = 0;
    v_buf.sem_op = 1;
    v_buf.sem_flg = SEM_UNDO;
 
    if (semop(semid, &v_buf, 1) == -1){
	perror("v(semid) failed");
	exit(1);
    } else
	return(0);
}//v()
 
****************************
testsem.c
/* program for testing p() and v() -- gets mutual exclusion */
 
#include "pv.h"
 
int main(void){
  key_t semkey = SEMKEY;
 
  if(fork() == 0) handlesem(semkey);
  else if(fork() == 0) handlesem(semkey);
  else if(fork() == 0) handlesem(semkey);
 
  while (wait ((int *) 0) >=0)
  removesem (semkeystr);
  return 0;
  }//main()
 
void handlesem(key_t skey){
  int semid, pid = getpid();
 
  /* initialize the semaphore if we just created it */
 
  if ((semid = initsem(skey)) < 0) exit(1);
 
  printf("\nprocess %d BEFORE critical section\n", pid);
 
  p(semid);
 
  printf("\nprocess %d in critical section \n", pid);
 
  sleep(10);
 
  printf("\nprocess %d leaving critical section \n", pid);
 
  v(semid); /* call semaphore SIGNAL operation */
 
  printf("\nprocess %d is OUTSIDE critical section and quitting!\n", pid);
  exit(0);
}

**fearyourself** · 26/03/2007, 10h02

Bonjour,

- Dois-je comprendre qu'on doit commenter un code qui ne vient pas de toi ?

- Quelles sont les parties que tu ne comprends pas ?

- As-tu lu la documentation des fonctions qui te posent problèmes ? http://man.developpez.com

Jc