利用共享内存实现的卖票系统：
利用flag来保证同一时间只有一个程序使用内存，使用结束还原。
#include <stdio.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/types.h>
#include <string.h>
#include <time.h>typedef struct _shm
{int flag;int ticket;
}SHM;void sellTicket(SHM* pshm)
{while (1){int time = rand() % 10 + 1; usleep(time*100000);if (pshm->flag == 1){pshm->flag = 0;if (pshm->ticket == 0) // 票卖完{pshm->flag = 1;break;}printf ("卖掉一张票，座位号是 : %d\n", pshm->ticket);pshm->ticket--;pshm->flag = 1;}}
}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;}// 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 负责对共享内存进行初始化if (argc == 2){pshm->flag = 1;pshm->ticket = 100;}// 开始卖票sellTicket(pshm);// 如果命令行参数等于2 负责对共享内存进行删除if (argc == 2){shmctl(shmid, IPC_RMID, NULL);}return 0;
}
利用信号量实现：
头文件：
#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__主函数：
#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;
}
)
