product-consume.c

一个生产者－消费者问题例子

#include<sys/types.h>
#include<sys/ipc.h>
#include<sys/sem.h>
#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<signal.h>
#include<time.h>

int semid1;
int semid2;
int semid3;
void ctrl_c(int);

int main()
{
	void(* old_handler)(int);
	old_handler=signal(SIGINT,ctrl_c);   //重定义ctrl+c

	int nsems=1;
	int flags=0666;
	int ptime;
	int ctime;
	pid_t pid;
	struct sembuf buf;
	printf("\n\n");
	printf("Now this is the producer's programe!\nAnd we have 5 rooms for buffer\n");
	printf("\n\n");
	semid1=semget(IPC_PRIVATE,nsems,flags); //建立三个信号量
	semid2=semget(IPC_PRIVATE,nsems,flags);
	semid3=semget(IPC_PRIVATE,nsems,flags);
	if(semid1<0||semid2<0||semid3<0)
	{
		perror("semget");
		exit(EXIT_FAILURE);
	}

	buf.sem_num=0;
	buf.sem_op=5;
	buf.sem_flg=0;

	if((semop(semid1,&buf,nsems))<0) //将semid1的semval定为5，即缓存区大小为5
	{
		perror("semop");
		exit(EXIT_FAILURE);
	}		
	
	buf.sem_op=1;
	if((semop(semid2,&buf,nsems))<0) //将semid2的semval定为1，来表示控制缓存区读写的信号量
	{
		perror("semop");
		exit(EXIT_FAILURE);
	}
	
	system("ipcs -s");
	printf("Now please enter the time by which the productor make a goods!\n\n");  //输入生产物品等待的时间，以便sleep（）函数调用。
	scanf("%d",&ptime);
	printf("Now please enter the time by which the consumer use a goods!\n\n");   //消费物品的时间
	scanf("%d",&ctime);
	
	pid=fork();
	if(pid>0)
	{		
		while(1)
		{
			sleep(ptime);
			printf("Now I make a new goods!\n\n");
			buf.sem_op=-1;
			semop(semid1,&buf,nsems);
			semop(semid2,&buf,nsems);
			printf("Now I add it to my buffer!\n\n");
			buf.sem_op=1;
			semop(semid3,&buf,nsems);
			semop(semid2,&buf,nsems);
		}
	}
	else
	{
		while(1)
		{
			buf.sem_op=-1;
			semop(semid3,&buf,nsems);
			semop(semid2,&buf,nsems);
			printf("Now I take one\n\n");		
			buf.sem_op=1;
			semop(semid1,&buf,nsems);
			semop(semid2,&buf,nsems);
			sleep(ctime);
			printf("I have already use the goods!\n\n");
		}
	}
}

void ctrl_c(int dump)    //当按下ctrl+c时，先将程序中建立的三个信号量删除，然后再退出。
{
	if((semctl(semid1,0,IPC_RMID))<0)
			exit(EXIT_FAILURE);
	else if((semctl(semid2,0,IPC_RMID))<0)
			exit(EXIT_FAILURE);	
	else if((semctl(semid3,0,IPC_RMID))<0)	
		exit(EXIT_FAILURE);	
	else	
		system("ipcs -s");	
	exit(EXIT_SUCCESS);
}