linux共享内存实验
发布时间：2018-7-31 10:22
发布者：嵌入式爱好
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更多技术文章地址：http://www.hqyj.com/news/emb211.htm?lcg-ee 1.实验目的 通过编写共享内存实验，进一步了解使用共享内存的具体步骤，同时加深对共享内存的理解。在本实验中，采用信号量作为同步机制完善两个进程(“生产者”和“消费者”)之间的通信，其功能类似于4.6节中的实例。在实例中使用信号量同步机制。 2.实验内容 该实现要求利用共享内存实现文件的打开和读写操作。 3.实验步骤 (1)画出流程图。该实验流程图如图1所示。 
图1 实验流程图 (2)编写代码。下面是共享内存缓冲区的数据结构的定义： /* shm_com.h */ #include #include #include #include #include #include #include #define SHM_BUFF_SZ 2048 struct shm_buff { int pid; char buffer[SHM_BUFF_SZ]; }; 以下是“生产者”程序部分： /* sem_com.h 和 sem_com.c 与4.4节示例中的同名程序相同 */ /* producer.c */ #include "shm_com.h" #include "sem_com.h" #include int ignore_signal(void) { /* 忽略一些信号，以免非法退出程序 */ signal(SIGINT, SIG_IGN); signal(SIGSTOP, SIG_IGN); signal(SIGQUIT, SIG_IGN); return 0; } int main() { void *shared_memory = NULL; struct shm_buff *shm_buff_inst; char buffer[BUFSIZ]; int shmid, semid; /* 定义信号量，用于实现访问共享内存的进程间的互斥 */ ignore_signal(); /* 防止程序非正常退出 */ semid = semget(ftok(".", 'a'), 1, 0666|IPC_CREAT); /* 创建一个信号量 */ init_sem(semid);/* 初始值为1 */ /* 创建共享内存 */ shmid = shmget(ftok(".", 'b'), sizeof(struct shm_buff), 0666|IPC_CREAT); if (shmid == -1) { perror("shmget failed"); del_sem(semid); exit(1); } /* 将共享内存地址映射到当前进程地址空间 */ shared_memory = shmat(shmid, (void*)0, 0); if (shared_memory == (void*)-1) { perror("shmat"); del_sem(semid); exit(1); } printf("Memory attached at %X\n", (int)shared_memory); /* 获得共享内存的映射地址 */ shm_buff_inst = (struct shared_use_st *)shared_memory; do { sem_p(semid); printf("Enter some text to the shared memory(enter 'quit' to exit):"); /* 向共享内存写入数据 */ if (fgets(shm_buff_inst->buffer, SHM_BUFF_SZ, stdin) == NULL) { perror("fgets"); sem_v(semid); break; } shm_buff_inst->pid = getpid(); sem_v(semid); } while(strncmp(shm_buff_inst->buffer, "quit", 4) != 0); /* 删除信号量 */ del_sem(semid); /* 删除共享内存到当前进程地址空间中的映射 */ if (shmdt(shared_memory) == 1) { perror("shmdt"); exit(1); } exit(0); } 以下是“消费者”程序部分： /* customer.c */ #include "shm_com.h" #include "sem_com.h" int main() { void *shared_memory = NULL; struct shm_buff *shm_buff_inst; int shmid, semid; /* 获得信号量 */ semid = semget(ftok(".", 'a'), 1, 0666); if (semid == -1) { perror("Producer is'nt exist"); exit(1); } /* 获得共享内存 */ shmid = shmget(ftok(".", 'b'), sizeof(struct shm_buff), 0666|IPC_CREAT); if (shmid == -1) { perror("shmget"); exit(1); } /* 将共享内存地址映射到当前进程地址空间 */ shared_memory = shmat(shmid, (void*)0, 0); if (shared_memory == (void*)-1) { perror("shmat"); exit(1); } printf("Memory attached at %X\n", (int)shared_memory); /* 获得共享内存的映射地址 */ shm_buff_inst = (struct shm_buff *)shared_memory; do { sem_p(semid); printf("Shared memory was written by process %d :%s", shm_buff_inst->pid, shm_buff_inst->buffer); if (strncmp(shm_buff_inst->buffer, "quit", 4) == 0) { break; } shm_buff_inst->pid = 0; memset(shm_buff_inst->buffer, 0, SHM_BUFF_SZ); sem_v(semid); } while(1); /* 删除共享内存到当前进程地址空间中的映射 */ if (shmdt(shared_memory) == -1) { perror("shmdt"); exit(1); } /* 删除共享内存 */ if (shmctl(shmid, IPC_RMID, NULL) == -1) { perror("shmctl(IPC_RMID)"); exit(1); } exit(0); } 4.实验结果 实验运行结果如下： $./producer Memory attached at B7F90000 Enter some text to the shared memory(enter 'quit' to exit):First message Enter some text to the shared memory(enter 'quit' to exit):Second message Enter some text to the shared memory(enter 'quit' to exit):quit $./customer Memory attached at B7FAF000 Shared memory was written by process 3815 :First message Shared memory was written by process 3815 :Second message Shared memory was written by process 3815 :quit |
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