【发布时间】：2021-01-19 22:47:24
【问题描述】：
这是我的问题：
- 创建进程
- 制作一个char缓冲区的共享变量
- 每个进程都会将一个 char 值（比如说 50 次），即“A”、“B”、“C”等写入共享内存，并在结束后打印出缓冲区大小
- 我需要添加 sleep 语句，以便将 char 值添加到共享值的顺序是这样的
Child -> Grand child 1 -> Grand child 2 -> Great Grand child 1 -> Great Grand child 2 - 最后打印最终缓冲区
所以首先我想创建这样的进程，父进程将有一个子进程。子进程将有孙子进程，每个孙子进程都会有曾孙子，如图所示。
我正在使用 IF-ELSE 结构来实现这一点，但我需要先创建所有进程然后开始工作，不知道如何实现这一点。我不知道代码进程没有向缓冲区或共享值添加任何内容有什么问题。我这样说的原因是当进程在执行后打印缓冲区大小时，每个进程都是相同的。
代码
#include <iostream>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include<stdio.h>
#include <sys/wait.h>
#include<sys/ipc.h>
#include<sys/shm.h>
using namespace std;
// Driver Code
int main()
{
// number of chars values the process will write
int child_chrs = 1000;
int grand_child1_chrs = 700;
int grand_child2_chrs = 300;
int great_grand_child1_chrs = 700;
int great_grand_child2_chrs = 300;
int fd[2];
pipe(fd);
int shared_index = 0, n =0;
write(fd[1], &n, sizeof(n));
key_t key = ftok("shmfile",65); // generate unique key
int shmid = shmget(key,1024,0666|IPC_CREAT); // get identifier in shmid
char *stringValue = (char*) shmat(shmid,(void*)0,0); // attach to shared memory
cout << "Parent process has been created." << endl;
cout << "Shared memory creation was successful." << endl;
if (fork() == 0) // Child
{
if(fork() == 0) // Grand Child 1
{
if(fork() == 0) // Great Grand Child 1
{
while(great_grand_child1_chrs!=0)
{
shared_index = read(fd[0], &shared_index, sizeof(int));
*(stringValue+shared_index) = 'Y';
great_grand_child1_chrs--;
shared_index++;
write(fd[1], &shared_index, sizeof(int));
}
cout << "From Great-grandchild1 process - I just finished and the buffer size = " << shared_index << endl;
cout << "From Great-grandchild1 process terminated normally\n";
}
else // Great Grand Child 2
{
while(grand_child1_chrs!=0)
{
shared_index = read(fd[0], &shared_index, sizeof(int));
*(stringValue+shared_index) = 'B';
grand_child1_chrs--;
shared_index++;
write(fd[1], &shared_index, sizeof(int));
}
cout << "From Great-grandchild2 process - I just finished and the buffer size = " << shared_index << endl;
cout << "From Great-grandchild2 process terminated normally\n";
}
}
else // Grand Child 2
{
if(fork() == 0) // Grand Child 1
{
if(fork() == 0) // Grand Child 2
{
while(great_grand_child2_chrs!=0)
{
shared_index = read(fd[0], &shared_index, sizeof(int));
*(stringValue+shared_index) = 'Z';
great_grand_child2_chrs--;
shared_index++;
write(fd[1], &shared_index, sizeof(int));
//cout<<"\nshared index: "<<shared_index;
}
cout << "From Grandchild1 process - I just finished and the buffer size = " << shared_index << endl;
cout << "The Grandchild1 process terminated normally.\n";
}
else // Grand Child 2
{
while(grand_child2_chrs!=0)
{
shared_index = read(fd[0], &shared_index, sizeof(int));
*(stringValue+shared_index) = 'C';
grand_child2_chrs--;
shared_index++;
write(fd[1], &shared_index, sizeof(int));
}
cout << "From Grandchild2 process - I just finished and the buffer size = " << shared_index << endl;
cout << "The Grandchild2 process terminated normally.\n";
}
}
else // Child
{
while(child_chrs!=0)
{
shared_index = read(fd[0], &shared_index, sizeof(int));
*(stringValue+shared_index) = 'A';
child_chrs--;
shared_index++;
write(fd[1], &shared_index, sizeof(int));
}
cout << "From Child process - I just finished and the buffer size = " << shared_index << endl;
cout << "The Child process terminated normally.\n";
}
}
}
else // Parent
{
wait(NULL);
cout<<"\n\nResultant Buffer is:\n\n";
cout << "From Parent process - I am exiting and final buffer size = " << shared_index << endl;
shmdt(stringValue);
cout << "Shared memory has been released.\n";
}
}
输出
From Child process - I just finished and the buffer size = 5
The Child process terminated normally.
Resultant Buffer is:
From Parent process - I am exiting and final buffer size = 0
Shared memory has been released.
From Grandchild2 process - I just finished and the buffer size = 5
The Grandchild2 process terminated normally.
注意：我知道代码是用 C++ 编写的，而且它必须是 C 语言。当我开始编写代码时，我发现的示例是用 C++ 编写的，但我没有进行使其成为 C 代码的更改。我可能会犯一些愚蠢的错误，因为我不是一个优秀的 C 程序员，我在 Java、Python、Ruby 和 C# 方面经验丰富，但 C 不是我有经验的。
【问题讨论】：
-
这是“你能把这个 C++ 代码转换成 C 吗？”
-
不，我不是要求转换，我会自己做，但由于我的代码没有按预期工作，我需要先修复它
-
shared_index = read(fd[0], &shared_index, sizeof(int));似乎是错误的。这将使用read（将是sizeof(int)、0或-1）的返回码覆盖您从管道中读取的数据。 -
另请注意，对于任何指针或数组
p和索引i，表达式*(p + i)完全 等于p[i]。后一种语法更易于阅读和编写。所以请不要写例如*(stringValue+shared_index)，而是stringValue[shared_index]。 -
旁注：家谱是继承的不良类比。派生类is-a 基类。所以在家谱中，孩子是父母，也是祖父母，这是没有意义的。请参阅 What is an example of the Liskov Substitution Principle? 了解一个方便的工具，以帮助了解继承层次结构何时有意义
标签： c++ fork shared-memory