From b675fb4053bfd292ffb3b3ba590c3c31904862b7 Mon Sep 17 00:00:00 2001
From: Rui Ribeiro <42305006+ruiribeiro04@users.noreply.github.com>
Date: Wed, 8 Oct 2025 22:31:22 +0100
Subject: [PATCH] Added new exercices

---
 rendu/limited_resources.c | 108 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 108 insertions(+)
 create mode 100644 rendu/limited_resources.c

diff --git a/rendu/limited_resources.c b/rendu/limited_resources.c
new file mode 100644
index 0000000..8ce6aa1
--- /dev/null
+++ b/rendu/limited_resources.c
@@ -0,0 +1,108 @@
+/* ************************************************************************** */
+/*                                                                            */
+/*                                                        :::      ::::::::   */
+/*   limited_resources.c                                :+:      :+:    :+:   */
+/*                                                    +:+ +:+         +:+     */
+/*   By: ruiferna <ruiferna@student.42porto.com>    +#+  +:+       +#+        */
+/*                                                +#+#+#+#+#+   +#+           */
+/*   Created: 2025/10/08 19:31:58 by ruiferna          #+#    #+#             */
+/*   Updated: 2025/10/08 21:10:18 by ruiferna         ###   ########.fr       */
+/*                                                                            */
+/* ************************************************************************** */
+
+#include <stdio.h>
+#include <pthread.h>
+#include <stdlib.h>
+#include <sys/time.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <time.h>
+
+#define STUDENTS 10
+
+/*
+- 3 computers (limited access)
+- Only 3 students can use the PC at same time
+- Implement a "semaphore" (using mutex, counter and condictions)
+*/
+
+typedef struct s_shared
+{
+	int pcs_available;
+	int students;
+	pthread_mutex_t pcs_available_mutex;
+	pthread_mutex_t students_mutex;
+}	t_shared;
+
+void *student_routine(void *arg)
+{
+	/*
+	Print when students:
+	- Arrive at the library
+	- Get a computer  
+	- Finish using the computer
+	- Leave the library
+	*/
+	t_shared *shared;
+	int student_id;
+	shared = (t_shared *) arg;
+	srand(time(NULL));
+	pthread_mutex_lock(&shared->students_mutex);
+	shared->students += 1;
+	student_id = shared->students;
+	printf("[%i] Student %i arrived at the library.\n", student_id, student_id);
+	pthread_mutex_unlock(&shared->students_mutex);
+	while (1)
+	{
+		pthread_mutex_lock(&shared->pcs_available_mutex);
+		if (shared->pcs_available > 0)
+		{
+			shared->pcs_available -= 1;
+			printf("[%i] Student %i got a computer.\n", student_id, student_id);
+			pthread_mutex_unlock(&shared->pcs_available_mutex);
+			break;
+		}
+		else
+		{
+			pthread_mutex_unlock(&shared->pcs_available_mutex);
+			usleep(100);
+		}
+	}
+	int use_time = 2 + rand() % 4;
+	usleep(use_time * 1000000);
+	pthread_mutex_lock(&shared->pcs_available_mutex);
+	shared->pcs_available += 1;
+	printf("[%i] Student %i finished using a computer.\n", student_id, student_id);
+	pthread_mutex_unlock(&shared->pcs_available_mutex);
+	printf("[%i] Student %i leaved the library.\n", student_id, student_id);
+	return (NULL);
+}
+
+int	main()
+{
+	pthread_t *students;
+	t_shared shared;
+
+	shared.pcs_available = 3;
+	shared.students = 0;
+	pthread_mutex_init(&shared.pcs_available_mutex, NULL);
+	pthread_mutex_init(&shared.students_mutex, NULL);
+	students = (pthread_t *) malloc (sizeof(pthread_t) * STUDENTS);
+
+	int i = 0;
+	while (i < STUDENTS)
+	{
+		pthread_create(&students[i], NULL, student_routine, &shared);
+		i++;
+	}
+	i = 0;
+	while (i < STUDENTS)
+	{
+		pthread_join(students[i], NULL);
+		i++;
+	}
+	pthread_mutex_destroy(&shared.pcs_available_mutex);
+	pthread_mutex_destroy(&shared.students_mutex);
+	free(students);
+	return (0);
+}
\ No newline at end of file