［Linux］内存共享

API

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头文件

#include <shm.h>

创建共享内存

int shmget(key_t key, size_t size, int shmflg);

key：键值，有效地为共享内存段命名
size：申请内存的大小

获取创建好的共享内存

void *shmat(int shm_id,const void *shm_addr, int shmflg);

shm_id：由shmget创建返回的共享内存id
shm_addr：指定物理共享内存映射到当前进程的此地址处，设为NULL时由OS决定

分离获得的共享内存

int shmdt(void *shm_addr);

shm_addr：shmat返回的本进程映射地址。
该函数只是让共享内存不再映射到本进程的地址范围内，并非释放共享内存

对共享内存进行操作

int shmctl(int shm_id, int command, struct shmid_ds *buf);

struct shmid_ds{
uid_t shm_perm.uid;
uid_t shm_perm.gid;
mode_t shm_perm.mode;
};
comman:

IPC_STAT
把shmid_ds中的数据设为共享内存的当前关联值
IPC_SET
如果有权限，把共享内存的内容设为shmid_ds中的数据
IPC_RMID
删除共享内存段

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Console下的通信

头文件

#include <unistd.h>#include <stdlib.h>#include <stdio.h>#include <string.h>#include <sys/shm.h>#define TEXT_SZ 2048struct shared_use_st{    int written_by_you;    char some_text[TEXT_SZ];};

Producer.c

#include "shm_com.h"int main(){    int running = 1;    void *shared_memory = NULL;    struct shared_use_st *shared_stuff;    char buffer[BUFSIZ];    int shmid;    //创建共享内存    shmid = shmget((key_t)2222, sizeof(struct shared_use_st), 0666|IPC_CREAT);    if(shmid == -1){        fprintf(stderr, "shmget failed.\n");        return 1;    }    //获取共享内存映射    shared_memory = shmat(shmid, NULL ,0);    if(shared_memory == (void *)-1){        fprintf(stderr, "shmat failed.\n");        return 1;    }    printf("Memory attached at %X.\n", (int)shared_memory);    shared_stuff = (struct shared_use_st *)shared_memory;    while(running){        //等待消费者改写数据（表示有消费者存在）        while(shared_stuff->written_by_you == 1){            sleep(1);            printf("Waiting for client ...\n");        }        printf("Enter some text: ");        fgets(buffer, BUFSIZ, stdin);        strncpy(shared_stuff->some_text, buffer, TEXT_SZ);        shared_stuff->written_by_you = 1;        if(strncmp(buffer, "end", 3) == 0){            running = 0;        }    }    //解除内存映射关系    if(shmdt(shared_memory) == -1){        fprintf(stderr, "shmdt failed.\n");        return 1;    }    return 0;}

Consumer.c

#include "shm_com.h"int main(){    int running = 1;    void *shared_memory = NULL;    struct shared_use_st *shared_stuff;    int shmid;    //创建共享内存    shmid = shmget((key_t)2222, sizeof(struct shared_use_st), 0666 | IPC_CREAT);    if(shmid == -1){        fprintf(stderr, "shmget failed.\n");        return 1;    }    //将共享内存地址映射到本进程    shared_memory = shmat(shmid, NULL, 0);    if(shared_memory == (void*)-1){        fprintf(stderr, "shmat failed.\n");        return 1;    }    printf("Memory attached at %X.\n", (int)shared_memory);    shared_stuff = (struct shared_use_st *)shared_memory;    shared_stuff -> written_by_you = 0;    while(running){        if(shared_stuff->written_by_you){            printf("You wrote:%s\n",shared_stuff->some_text);            sleep(rand()%4);            shared_stuff->written_by_you = 0;            if(strncmp(shared_stuff->some_text, "end", 3) == 0){                running = 0;            }        }    }    //分离共享内存    if(shmdt(shared_memory) == -1){        fprintf(stderr, "shmdt failed.\n");        return 1;    }    //释放共享内存    if(shmctl(shmid, IPC_RMID, 0) == -1){        fprintf(stderr, "shmctl(IPC_RMID) failed.\n");        return 1;    }    return 0;}