#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <semaphore.h>
#include <unistd.h>

#define N 5 // 阅览室容量
#define M 8 // 学生总数

unsigned int ns = 0; // 学生计数
sem_t sem; // 信号量，用于限制学生数量
sem_t wfm; // 等待管理员开门的信号量
sem_t wfs; // 等待学生离开的信号量
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER; // 互斥锁，用于保护共享资源

void *Student(void *i) {
    long id = (long)i; // 学生编号
    printf("Student %ld is entering...\n", id);
    sem_wait(&sem); // 等待信号量
    pthread_mutex_lock(&mutex); // 加锁保护共享资源
    ns++;
    if (ns == 1) {
        sem_wait(&wfm);
        printf("The 1st student entered.\n");
    }
    pthread_mutex_unlock(&mutex); // 解锁
    printf("Student %ld has been entered.\n", id);
    // 阅读
    int time = rand() % 10 + 1; // 随机阅读时间（1-10秒）
    sleep(time);
    printf("Student %ld is going to leave...\n", id);
    pthread_mutex_lock(&mutex); // 加锁保护共享资源
    ns--;
    printf("Student %ld has left.\n", id);
    if (ns == 0) {
        sem_post(&wfs);
        printf("The last student left.\n");
    }
    pthread_mutex_unlock(&mutex); // 解锁
    sem_post(&sem); // 释放信号量，允许下一个学生进入
    pthread_exit(NULL);
}

void *Manager() {
    printf("Manager open door.\n");
    sem_post(&wfm);
    printf("Manager is waiting for all students to leave.\n");
    sem_wait(&wfs);
    printf("Manager close door.\n");
    pthread_exit(NULL);
}

int main() {
    // 初始化信号量
    sem_init(&sem, 0, N);
    sem_init(&wfm, 0, 1);
    sem_init(&wfs, 0, 0);

    // 创建M个学生线程
    pthread_t students[M];
    for (long i = 0; i < M; i++) {
        pthread_create(&students[i], NULL, Student, (void *)i);
    }

    // 创建管理员线程
    pthread_t manager;
    pthread_create(&manager, NULL, Manager, NULL);
    // 等待所有学生线程结束
    for (long i = 0; i < M; i++) {
        pthread_join(students[i], NULL);
    }

    // 等待管理员线程结束
    pthread_join(manager, NULL);

    // 销毁信号量
    sem_destroy(&sem);
    sem_destroy(&wfm);
    sem_destroy(&wfs);

    return 0;
}