process.c

/**
 * Process 3 (le père), éffectuera un display_msg uniquement quand le process 1
 * et 2 aura terminé. 
 *
 * Un set de deux sémaphores est donc utilisé.
 *
 * Ne pas oublier de liberer les ressources fork (waitpid) et de delete le set
 * de sémaphores
 */
#define _XOPEN_SOURCE

#include <unistd.h>
#include <stdlib.h> 
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <stdio.h>
#include <wait.h>

#define SEM_UN 0
#define SEM_DEUX 1

void exit_error(char * message)
{
	perror(message);
	exit(EXIT_FAILURE);
}

void display_msg(char * message)
{
	for (int i = 0; i < 10; ++i)
	{
		printf("%s :: %d \n", message, i);
		sleep(1);
	}
}

int main()
{

	int pid1, pid2, sem;

	if ((sem = semget(IPC_PRIVATE, 2, IPC_CREAT | 0666)) == -1) // Un set de 2 sem
		exit_error("Erreur semget");

	if (semctl(sem, SEM_UN, SETVAL, 0) == -1)
		exit_error("erreur semctl 0");

	if (semctl(sem, SEM_DEUX, SETVAL, 0) == -1)
		exit_error("erreur semctl 1");

	struct sembuf up = {0, 1, 0}; // up.sem_op = 1; up.sem_flg = 0;
	struct sembuf down = {0, -1, 0}; //	down.sem_op = -1; down.sem_flg = 0;

	pid1 = fork();
	if (pid1== 0)
	{
		display_msg("Process 1");
		up.sem_num = SEM_UN;
		semop(sem, &up, 1);
		exit(EXIT_SUCCESS);
	}
	else if (pid1 == -1)
	{
		exit_error("Erreur fork pid1");
	}

	pid2 = fork();
	if (pid2 == 0)
	{
		display_msg("Process 2");
		up.sem_num = SEM_DEUX;
		semop(sem, &up, 1);
		exit(EXIT_SUCCESS);
	}
	else if (pid2 == -1)
	{
		exit_error("Erreur fork pid2");
	}

	down.sem_num = SEM_UN;
	semop(sem, &down, 1);

	down.sem_num = SEM_DEUX;
	semop(sem, &down, 1);

	display_msg("Process 3");

	// while (waitpid(-1, NULL, WNOHANG) > 0); 
	waitpid(pid1, NULL, 0);
	waitpid(pid2, NULL, 0);

	if ( semctl(sem, SEM_UN, IPC_RMID) == -1)
		exit_error("Delete set sem");

	exit(EXIT_SUCCESS);
}