操作系统课程设计：用多线程同步方法解决读者阅览问题

最近六级考完，没啥事。刚好有门操作系统课程设计，于是就打开了阔别已久的虚拟机。。。。

#include <stdio.h>
#include <pthread.h>
#include <semaphore.h>
#include <time.h>

int number=0;             //馆内的人数；
int buffer[5]={-1,-1,-1,-1,-1};   //-1代表空座位
sem_t sem;                  //信号量
pthread_mutex_t mutex;

void *thr_fn(void * pth_id)
{   
    int chair_id, reader_id;
    int time;
    reader_id = *(int *)pth_id ;
    sleep(1);
    pthread_mutex_lock(&mutex);
    printf("No.%d Reader  Entered!\n",	reader_id);
    number++;
    printf("%d people in the reading room...\n",number);
    pthread_mutex_unlock(&mutex);
    
    
    sem_wait(&sem);
    for(chair_id = 0;chair_id < 5 ;chair_id++){
      if(buffer[chair_id] == -1){
	  buffer[chair_id] = reader_id;
	  break;
	}
     }
    printf("No.%d Reader  sit at No.%d Seat\n",reader_id,chair_id + 1);
    time = rand() % 50;
    sleep(time + 3);
    printf("No.%d Reader  has been finished reading, Exit!\n",reader_id );
    buffer[chair_id] = -1;
    sem_post(&sem);

    pthread_mutex_lock(&mutex);
    number--;
    pthread_mutex_unlock(&mutex);
    
    pthread_exit;
}

int main(void){
    int err,t_id,j;
    void *pth_id;
    pth_id = &t_id;
    pthread_t t[10];
    pthread_mutex_init(&mutex,NULL);
    sem_init(&sem,0,5);
    for(t_id = 0; t_id < 10;t_id++){
        err=pthread_create(&t[t_id],NULL,thr_fn,pth_id);
	  if(err != 0)
		printf("ERROR! CREATE THREAD FAILED!!!\n");
	  else
		printf("No.%d THREAD READY.\n",t_id);
        }
　　for(i = 0, i<10, i++)
　　　　pthread_join(t[i],NULL);
　　return 0;
}

 这段多线程的实现的是阅览室占座问题。打印结果时似乎有点小问题，能交差就好。。。