用共享内存和信号量实现的简单的卖票系统

#ifndef __SEMAPHORE_H__
#define __SEMAPHORE_H__

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>

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) */
};

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

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

return ret;
}

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

return ret;
}

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

#endif // __SEMAPHORE_H__

#include <stdio.h>#include <sys/ipc.h>#include <sys/shm.h>#include <sys/types.h>#include <string.h>#include <time.h>#include "semaphore.h"typedef struct _shm{int flag;int ticket;}SHM;void sellTicket(SHM* pshm, int sem_id){while (1){int time = rand() % 10 +
1; usleep(time*100000);// 信号量的P操作sem_p (sem_id);if (pshm->ticket == 0) // 票卖完{sem_v (sem_id);break;}printf ("卖掉一张票，座位号是 : %d\n", pshm->ticket);pshm->ticket--;sem_v (sem_id);}}int main(int argc, char **argv){srand ((unsigned int)time(NULL));// 1、创建或者获取一个共享内存int
shmid = shmget((key_t)1234, sizeof(SHM), 0666 | IPC_CREAT);if (shmid == -1){perror ("shmget");return -1;}// 创建一个信号量int sem_id = semget((key_t)5678, 1, 0666 | IPC_CREAT);if (sem_id== -1){perror ("semget");return -1;}// 2、将共享内存映射到当前的进程空间SHM* pshm = (SHM*)shmat(shmid,
NULL, 0);if(pshm == (SHM*)-1){perror ("shmat");return -1;}// 如果命令行参数等于2 负责对共享内存和信号量进行初始化if (argc == 2){pshm->ticket = 100;sem_init(sem_id);}// 开始卖票sellTicket(pshm, sem_id);// 如果命令行参数等于2 负责对共享内存和信号量进行删除if (argc == 2){shmctl(shmid, IPC_RMID, NULL);sem_del(sem_id);}return
0;}