philosopher.c

操作系统课程设计

#include <stdio.h>
#include <unistd.h>
#include <limits.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <sys/shm.h>
#include <time.h>

#define N 5  //哲学家个数
#define LEFT (i+N-1)%N //i左边的哲学家
#define RIGHT (i+1)%N //i右边的哲学家
#define THINKING 0
#define HUNGRY 1
#define EATING 2

//共享内存的结构
typedef struct{
	int state[N];//哲学家的状态
	int count;//就餐哲学家的个数
} shared_sum;

static int semid;//标记信号量集
static shared_sum *sharedsum;//实现共享内存的指针


//创建编号为0~N的N+1个信号量，第N个信号量为MUTEX信号量
void create()
{
	int semnum;
	if((semid = semget(IPC_PRIVATE,N+1,0666))==-1)//创建信号量集
		perror("failed to create semaphore");
	for(semnum=0;semnum<=N;semnum++)
	{
		if(semctl(semid,semnum,SETVAL,1)==-1)//初始化各信号量
			perror("failed to set semaphore");
	}
}

//开辟共享内存区，存储哲学家状态
int  shmem()
{
	int shid;
	int num;
	shid = shmget(IPC_PRIVATE,sizeof(shared_sum),IPC_CREAT|0666);//开辟内存区
	
	if(shid ==-1)
	{
		if(((shid = shmget(IPC_PRIVATE,sizeof(shared_sum),IPC_CREAT|0664))==-1)||
		        ((sharedsum = (shared_sum *)shmat(shid,NULL,0)) == (void *)-1))
		        {
		        	return -1;
		        }
	}
	else
	{
		sharedsum = (shared_sum *)shmat(shid,NULL,0);//内存区数据关联
		if(sharedsum ==(void *)-1)
			return -1;

		//共享内存初始化
		for(num=0;num<N;num++)
			sharedsum->state[num] = 0;
		sharedsum->count = 0;
	}
	return 0;
	
}

//某个信号量的up操作
void up(int num)
{
    struct sembuf v_buf = {num,1,SEM_UNDO};
    
    semop(semid,&v_buf,1);
}

//某个信号量的down操作
void down(int num)
{
    struct sembuf p_buf = {num,-1,SEM_UNDO};
    
    semop(semid,&p_buf,1);
}

//检查是否可吃
void test(int i)
{
	int count;
	int j;
	if(sharedsum->state[i] == HUNGRY && sharedsum->state[LEFT]!=EATING && sharedsum->state[RIGHT]!=EATING)
	{
		sharedsum->state[i] = EATING;
		up(i);
		printf("philosopher ");
		for(j=0;j<N;j++)//输出某一时刻处于吃状态的哲学家
		{
			if(sharedsum->state[j] == EATING)
			          printf("%d ",j);
		}
		printf("now are eating\n");
	}
}

//拿起叉子
void take_forks(int i)
{
	down(N);//进入临界区
	sharedsum->state[i] = HUNGRY;
	test(i);//尝试获取两把叉子
	up(N);//离开临界区
	down(i);//如果得不到需要的叉子则阻塞
	
}

//放下叉子
void put_forks(int i)
{
	down(N);//进入临界区
	sharedsum->state[i] = THINKING;
	test(LEFT);//检查左边的哲学家现在可以吃吗
	test(RIGHT);//检查右边的哲学家现在可以吃吗
	up(N);//离开临界区
}

//代表一个哲学家
void philosopher(int i)
{
	int j;
	time_t t;

    srand((unsigned) time(&t));//初始化随机数发生器
	for(j=0;j<10;j++)
	{
		printf("philosopher %d is thinking\n",i);
		take_forks(i);	//要求得到两把叉子或被阻塞
		usleep(rand() % 100);//随机睡眠0~100毫秒
		put_forks(i);//把两把叉子入回桌子 

	}
}


int main()
{
	pid_t pid[5];
	int i;
	create();
	if(shmem()==-1)
	{
		return -1;
	}
	for(i=0;i<5;i++)//创建5个哲学家
	{
		pid[i]=fork();
		if(pid[i] == 0)
		{
			philosopher(i);//运行哲学家函数
			return 0;
		}
	}
	for(i=0;i<5;i++)
		wait();//等待子进程结束
	return 0;
}