From 20b3bffac789da5e1eb381a452ad6b333c311626 Mon Sep 17 00:00:00 2001
From: Lukas Jiriste <ljiriste@student.42prague.com>
Date: Thu, 23 May 2024 09:52:46 +0200
Subject: [PATCH] Add semaphore to each philo

To react fast to starving philosopher, there has to be another thread
checking the state of the philo. Because of this there has to be
a mechanism to prevent data race. Because mutexes are forbidden
it has to be a semaphore.
This commit contains the semaphore and some code that dictates
its usage.
---
 philo_bonus/philo.c | 45 +++++++++++++++++++++++++++++++--------------
 philo_bonus/philo.h |  1 +
 2 files changed, 32 insertions(+), 14 deletions(-)

diff --git a/philo_bonus/philo.c b/philo_bonus/philo.c
index 5acbb9e..9550f0c 100644
--- a/philo_bonus/philo.c
+++ b/philo_bonus/philo.c
@@ -6,19 +6,34 @@
 /*   By: ljiriste <marvin@42.fr>                    +#+  +:+       +#+        */
 /*                                                +#+#+#+#+#+   +#+           */
 /*   Created: 2024/05/09 08:45:21 by ljiriste          #+#    #+#             */
-/*   Updated: 2024/05/12 21:52:05 by ljiriste         ###   ########.fr       */
+/*   Updated: 2024/05/23 09:50:14 by ljiriste         ###   ########.fr       */
 /*                                                                            */
 /* ************************************************************************** */
 
 #include "philo.h"
 #include <unistd.h>
+#include <stdio.h>
+#include <stdlib.h>
 
-static void	open_semaphores(sem_t *semaphores[sem_num])
+static void	open_semaphores(t_philo *philo)
 {
-	semaphores[forks] = sem_open(FORKS_SEM, 0);
-	semaphores[fed] = sem_open(WELL_FED_SEM, 0);
-	semaphores[death] = sem_open(DEATH_SEM, 0);
-	semaphores[term] = sem_open(TERM_SEM, 0);
+	char	*sem_name;
+
+	philo->semaphores[forks] = sem_open(FORKS_SEM, 0);
+	philo->semaphores[fed] = sem_open(WELL_FED_SEM, 0);
+	philo->semaphores[death] = sem_open(DEATH_SEM, 0);
+	philo->semaphores[term] = sem_open(TERM_SEM, 0);
+	sem_name = create_philo_sem_name(philo->id);
+	philo->philo_sem = sem_open(sem_name, O_CREAT | O_EXCL, S_IRUSR | S_IWUSR, 1);
+	free(sem_name);
+	if (philo->philo_sem == SEM_FAILED)
+	{
+		sem_wait(philo->semaphores[term]);
+		printf("An error has occured.\n");
+		sem_wait(philo->semaphores[death]);
+		exit(2);
+	}
+	return ;
 }
 
 static void	philo_think(t_philo *philo)
@@ -29,17 +44,14 @@ static void	philo_think(t_philo *philo)
 
 static void	philo_eat(t_philo *philo)
 {
-	useconds_t	time_now;
-
 	sem_wait(philo->semaphores[forks]);
 	print_timestamp(philo, "has taken a fork");
 	sem_wait(philo->semaphores[forks]);
 	print_timestamp(philo, "has taken a fork");
-	time_now = usecs_since_start(philo->settings.start);
-	if (time_now - philo->last_eaten > philo->settings.time_to_die)
-		die(philo);
-	philo->last_eaten = time_now;
+	sem_wait(philo->philo_sem);
+	philo->last_eaten = usecs_since_start(philo->settings.start);
 	++philo->num_eaten;
+	sem_post(philo->philo_sem);
 	print_timestamp(philo, "is eating");
 	if (philo->settings.should_check_hunger &&
 		philo->num_eaten == philo->settings.min_eat_num)
@@ -59,11 +71,16 @@ static void	philo_sleep(t_philo *philo)
 
 void	be_a_philosopher(t_philo *philo)
 {
-	open_semaphores(philo->semaphores);
-	while (1)
+	pid_t	hunger_watcher_pid;
+
+	open_semaphores(philo);
+	hunger_watcher_pid = create_hunger_watcher(philo);
+	while (is_alive(philo))
 	{
 		philo_think(philo);
 		philo_eat(philo);
 		philo_sleep(philo);
 	}
+	destroy_hunger_watcher(hunger_watcher_pid);
+	exit(0);
 }
diff --git a/philo_bonus/philo.h b/philo_bonus/philo.h
index 7f1e43e..8b3a1d6 100644
--- a/philo_bonus/philo.h
+++ b/philo_bonus/philo.h
@@ -60,6 +60,7 @@ typedef struct s_philosopher
 	unsigned int	id;
 	useconds_t		last_eaten;
 	sem_t			*semaphores[sem_num];
+	sem_t			*philo_sem;
 	t_settings		settings;
 }					t_philo;
 
-- 
2.30.2