以卖票为列的共享内存和信号量的学习

经典桥段:李老师卖票

1 通过共享内存实现

//shmid  创建并获取共享内存
#include 
#include 
//shmat  映射共享内存  解除映射
#include 
#include 
//删除共享内存
 #include  
 #include 

#include 
#include 
#include 

typedef struct _shm
{
	int flag;    //锁
	int ticket;  //票
}SHM;

void sell_ticket(SHM* shmp)
{
	while(1)
	{
		int time = rand()%10 + 1;
		usleep(time * 100000);
		if(shmp->flag == 1)
		{
			shmp->flag = 0;
			if(shmp->ticket == 0)
			{
				shmp->flag = 1;
				break;
			}
			printf("卖了第%d张票\n",shmp->ticket);
			shmp->ticket--;
			shmp->flag = 1;
		}
	}
}


int main(int argc,char ** argv)
{
	srand((unsigned int)time(NULL));
	
	//创建贡献内存
	int shmid = shmget((key_t)1234,sizeof(SHM),0666|IPC_CREAT);   //加一个创建宏
	if(shmid == -1)
	{
		perror("shmget");
		return -1;
	}
	
	//映射共享内存
	SHM * shmp = (SHM*)shmat(shmid,NULL,0);
	
	if(argc == 2)
	{
		shmp->flag = 1;
		shmp->ticket = 100;
	}
	
	sell_ticket(shmp);
	
	if(argc == 2)
	{
		//解除共享内存
		shmdt(shmp);
		
		//删除共享内存
		shmctl(shmid,IPC_RMID,NULL);  //删除宏
	}
	
	return 0;
}

2 通过信号量实现的卖票系统

头文件

#ifndef __SEMAPHORE_H__
#define __SEMAPHORE_H__

//控制信号量 semctl  用于初始化和删除  operate(操作)
#include 
#include 
#include 

//操作信号量 semop  用于P操作和V操作   control(控制)
#include 
#include 
#include 

//创建信号量 semget
#include 
#include 
#include 

union semun 
{
   int              val;    /* Value for SETVAL */
   struct semid_ds *buf;    /* Buffer for IPC_STAT, IPC_SET */
   unsigned short  *array;  /* Array for GETALL, SETALL */
   struct seminfo  *__buf;  /* Buffer for IPC_INFO
							   (Linux specific) */
};


//初始化信号量
int sem_init(int sem_id)
{
	union semun sem;
	sem.val = 1;
	int ret = semctl(sem_id, 0, SETVAL, sem);
	return ret;
}

//信号量p操作
int sem_p(int sem_id)
{
	struct sembuf sem;
	sem.sem_num = 0;
	sem.sem_op = -1;   //p操作
	sem.sem_flg = SEM_UNDO;
	
	int ret = semop(sem_id, &sem, 1);
	return ret;
}

//信号量v操作
int sem_v(int sem_id)
{
	struct sembuf sem;
	sem.sem_num = 0;
	sem.sem_op = 1;   //v操作
	sem.sem_flg = SEM_UNDO;
	
	int ret = semop(sem_id, &sem, 1);
	return ret;
}


//删除信号量
int sem_del(int sem_id)
{
	int ret = semctl(sem_id, 0, IPC_RMID);
	return ret;
}

#endif

实现函数

//shmid  创建并获取共享内存
#include 
#include 
//shmat  映射共享内存  解除映射
#include 
#include 
//删除共享内存
#include  
#include 
//信号量
#include "semaphore.h"

#include 
#include 
#include 

typedef struct _shm
{
	int ticket;  //票
}SHM;

void sell_ticket(SHM* shmp,int sem_id)
{
	while(1)
	{
		int time = rand()%10 + 1;
		usleep(time * 1000);
		
		//p操作
		sem_p(sem_id);

		if(shmp->ticket == 0)  //票卖完
		{
			sem_v(sem_id);
			break;
		}
		printf("卖了第%d张票\n",shmp->ticket);
		shmp->ticket--;
		
		//v操作
		sem_v(sem_id);
	}
}


int main(int argc,char ** argv)
{
	srand((unsigned int)time(NULL));
	
	//创建共享内存
	int shmid = shmget((key_t)1234,sizeof(SHM),0666|IPC_CREAT);   //加一个创建宏
	if(shmid == -1)
	{
		perror("shmget");
		return -1;
	}
	
	//创建信号量
	int sem_id = semget((key_t)2345 , 1, 0666|IPC_CREAT);
	if(sem_id == -1)
	{
		perror("shmget");
		return -1;
	}
	
	//映射共享内存
	SHM * shmp = (SHM*)shmat(shmid,NULL,0);
	
	if(argc == 2)
	{
		//初始化信号量
		sem_init(sem_id);
		shmp->ticket = 100;
	}
	
	sell_ticket(shmp,sem_id);
	
	if(argc == 2)
	{
		//解除共享内存
		shmdt(shmp);
		
		//删除共享内存
		shmctl(shmid,IPC_RMID,NULL);  //删除宏
		//删除信号量
		sem_del(sem_id);
	}
	
	return 0;
}