从共享内存段复制数据会导致客户端出现段错误（信号量和共享内存）

Posted 2023-02-22

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【中文标题】从共享内存段复制数据会导致客户端出现段错误（信号量和共享内存）【英文标题】：Copying Data from Shared memory segment causes seg fault in the client ( semaphores & shared memory) 【发布时间】：2014-03-20 01:38:50 【问题描述】：

我正在尝试编写一个简单的生产者和消费者程序（两个不相关的进程）。，具有共享内存和信号量。我使用信号量 empty & full 作为条件变量，并将数据从生产者 memcpy 到共享内存段中。而且，我尝试将数据存储到消费者的局部变量中，但这会导致段错误。这很奇怪，我无法弄清楚发生了什么。这是代码。

生产者和消费者的共同部分（信号量和共享内存创建）：

#include <stdio.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <string.h>
#include<stdlib.h>
#include <sys/shm.h>

struct a

int a;
int b;
a_s;
void wait(int semid)

int err,nsops=1;
struct sembuf *sops = (struct sembuf *) malloc(sizeof(struct sembuf));
sops[0].sem_num = 0;
sops[0].sem_op = -1;
sops[0].sem_flg = 0;
err=semop(semid, sops, nsops);
if(err < 0)
    printf(" unable to do the sop \n");


void signal(int semid)

int err,nsops=1;
struct sembuf *sops = (struct sembuf *) malloc(sizeof(struct sembuf));      
sops[0].sem_num = 0;
sops[0].sem_op = 1;
sops[0].sem_flg = 0;
err=semop(semid, sops, nsops);
if(err < 0)
    printf(" unable to do the sop \n");



int main()

int i, err;
int full,empty;
key_t full_key = 1234, empty_key = 5678;
int sem_flg = IPC_CREAT | 0666;
int nsems = 1;
int nsops = 2;
    int shmid;
void *string;
void *s;
int shm_key = 9999;

struct a *a_str;
/*****************************************/

empty = semget(empty_key, nsems, sem_flg);
if(empty < 0)
    printf(" failed to initialize the semaphore \n");

semctl(empty, 0, SETVAL, 1) ;
/****************************************/
full = semget(full_key, nsems, sem_flg);
if(full < 0)
    printf(" failed to initialize the semaphore \n");

semctl(full, 0, SETVAL, 0) ;    

/*****************************************/
shmid = shmget(shm_key, 30, IPC_CREAT|0666); 
if(shmid < 0) 
    printf(" unable to create shmem \n");
else
    printf(" created shm \n");

string = shmat( shmid, NULL, 0); 
if( string == (void * ) (-1))
    printf(" unable to attach the string \n");
else
    printf(" success with shmat \n");
s = string;
/******************************************/

生产者：输入数据

while(1)

    wait(empty);
    sleep(1);
    memcpy( string, (void *) a_str, sizeof(struct a));
    printf(" wrote the string \n");
    signal(full);

消费者：复制数据并显示

while(1)


wait(full);
printf(" after full \n");
memcpy((void *)a_str, (void *)s, sizeof(struct a));
printf(" copied the memory from string \n");
printf(" a %d b %d \n",((struct a *)a_str)->a, ((struct a *)a_str)->b);
sleep(1);
memcpy(s, string, 7);


signal(empty);


return 0;

谁能告诉我为什么它的段错误？我只是从内存段复制地址。可能会出什么问题？

【问题讨论】：

【参考方案1】：