Linux共享内存流程图,linux共享内存实验

本文关键字： 内存共享

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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