some-usable-scripts/c/semaphores_manuel_exemples/exercice_rw/sema.c

#include <stdlib.h>
#include <assert.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdarg.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include "sema.h"

typedef unsigned short int ushort;

int creat_sem(key_t cle,int val)
{
	int semid;

	union semun{
	    int val;
	    struct semid_ds *buf;
	    ushort *array;
    } arg;

    if((semid=semget(cle,1,0666+IPC_CREAT+IPC_EXCL))>= 0)
    {
		arg.val=val;
		if(semctl(semid,0,SETVAL,arg)< 0)
			semid = -1;
    }
    return(semid);
}
int del_sem(key_t cle)
{
    return(semctl((semget(cle,0,0)),0,IPC_RMID,0));
}
int open_sem(key_t cle)
{
	return(semget(cle,0,0));
}

void P(int semid)
{
	struct sembuf psembuf;

	psembuf.sem_op = -1;
	psembuf.sem_flg = 0;
	psembuf.sem_num = 0;
	semop(semid,&psembuf,1);
}

void V(int semid)
{
	struct sembuf vsembuf;

	vsembuf.sem_op = 1;
	vsembuf.sem_flg = 0;
	vsembuf.sem_num = 0;
	semop(semid,&vsembuf,1);
}