以卖票为列的共享内存和信号量的学习

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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 <sys/ipc.h>#include <sys/shm.h>//shmat  映射共享内存  解除映射#include <sys/types.h>#include <sys/shm.h>//删除共享内存 #include <sys/ipc.h>  #include <sys/shm.h>#include <stdio.h>#include <string.h>#include <time.h>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 <sys/types.h>#include <sys/ipc.h>#include <sys/sem.h>//操作信号量 semop  用于P操作和V操作   control(控制)#include <sys/types.h>#include <sys/ipc.h>#include <sys/sem.h>//创建信号量 semget#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) */};//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 <sys/ipc.h>#include <sys/shm.h>//shmat  映射共享内存  解除映射#include <sys/types.h>#include <sys/shm.h>//删除共享内存#include <sys/ipc.h> #include <sys/shm.h>//信号量#include "semaphore.h"#include <stdio.h>#include <string.h>#include <time.h>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;}

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