如何使用共享内存在两个进程之间进行通信 [英] how to use shared memory to communicate between two processes

问题描述

我正在尝试在两个进程之间进行通信.我正在尝试在一个进程中将数据(如姓名、电话号码、地址)保存到共享内存中，并尝试通过其他进程打印该数据.

I am trying to communicate between two processes. I am trying to save data(like name, phone number, address) to shared memory in one process and trying to print that data through other process.

process1.c

#include <stdio.h>
#include <sys/shm.h>
#include <sys/stat.h>
int main ()
{
  int segment_id;
  char* shared_memory[3];
  int segment_size;
  key_t shm_key;
  int i=0;
  const int shared_segment_size = 0x6400;
  /* Allocate a shared memory segment. */
  segment_id = shmget (shm_key, shared_segment_size,
            IPC_CREAT | IPC_EXCL | S_IRUSR | S_IWUSR);
  /* Attach the shared memory segment. */
  shared_memory[3] = (char*) shmat (segment_id, 0, 0);
  printf ("shared memory attached at address %p
", shared_memory);
  /* Write a string to the shared memory segment. */
   sprintf(shared_memory[i], "maddy 
");
   sprintf(shared_memory[i+1], "73453916
");
   sprintf(shared_memory[i+2], "america
");

  /*calling the other process*/
  system("./process2");

  /* Detach the shared memory segment. */
  shmdt (shared_memory);
  /* Deallocate the shared memory segment.*/
  shmctl (segment_id, IPC_RMID, 0);

  return 0;
}

<小时>

process2.c

---

process2.c

#include <stdio.h>
#include <sys/shm.h>
#include <sys/stat.h>
int main ()
{
  int segment_id;
  char* shared_memory[3];
  int segment_size;
  int i=0;
  key_t shm_key;
  const int shared_segment_size = 0x6400;
  /* Allocate a shared memory segment. */
  segment_id = shmget (shm_key, shared_segment_size,
              S_IRUSR | S_IWUSR);
  /* Attach the shared memory segment. */
  shared_memory[3] = (char*) shmat (segment_id, 0, 0);
  printf ("shared memory22 attached at address %p
", shared_memory);
   printf ("name=%s
", shared_memory[i]);
   printf ("%s
", shared_memory[i+1]);
   printf ("%s
", shared_memory[i+2]);
  /* Detach the shared memory segment. */
  shmdt (shared_memory);
   return 0;
}

但是我没有得到想要的输出.我得到的输出是:

But I am not getting the desired output. the output which i got is:

shared memory attached at address 0x7fff0fd2d460
Segmentation fault

任何人都可以帮我解决这个问题.这是初始化 shared_memory[3] 的正确方法吗.

Anyone can please help me with this. Is this the correct way of initializing shared_memory[3].

谢谢.

推荐答案

char* shared_memory[3];
...
shared_memory[3] = (char*) shmat (segment_id, 0, 0);

您将 shared_memory 声明为一个能够保存三个指向 char 的指针的数组，但您实际上用它来做的是在数组末尾的后面写一个指针.由于不知道那里的内存是用来做什么的，接下来会发生什么通常是不可预测的.

You declare shared_memory as an array capable of holding three pointers to char, but what you actually do with it is to write a pointer one place behind the end of the array. Since there is no telling what the memory there is otherwise used for, what happens next is generally unpredictable.

当您尝试使用 shared_memory[0] 到 shared_memory[2] 中的指针时，事情最终会变得很糟糕，因为这些指针从未被初始化.它们充满了来自堆栈的无意义垃圾——因此是分段错误.

Things go conclusively bad afterwards when you try to make use of the pointers in shared_memory[0] through shared_memory[2], because those pointers have never been initialized. They are filled with meaningless garbage from the stack -- thus the segmentation fault.

一般来说，您似乎无法区分数组及其元素.在尝试使用共享内存 IPC 之前，您应该让自己更多熟悉顺序代码中的数组和指针.

It seems, in general, that you're failing to distinguish between the array and its elements. You should go and make yourself a lot more comfortable with arrays and pointers in sequential code before you try your hand at shared-memory IPC.

请注意，共享内存是进行 IPC 的一种更容易出错的方式.除非您有严格的效率限制并且要交换大量数据，否则使用管道、命名管道或套接字要容易得多.

Note that shared memory is one of the more easy-to-get-wrong ways of doing IPC out there. Unless you have rigid efficiency constraints and are going to exchange a lot of data, it's much easier to work with pipes, named pipes, or sockets.

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