分叉和执行许多不同的过程，并从每个过程中获取结果 [英] fork and exec many different processes, and obtain results from each one

问题描述

我设法从应用程序中派生并执行了一个不同的程序.我目前正在研究如何等待exec调用的过程通过管道或stdout返回结果.但是，我可以使用单个fork来处理一组进程吗?还是必须多次进行fork并再次调用同一程序?我可以为每个不同的过程获取PID吗?我希望我的应用程序调用我当前正在多次调用的同一程序，但参数不同:我希望一组8个进程运行同一程序，并通过管道返回结果.有人可以给我指出正确的方向吗?我已经阅读了linux.die手册页，但是它们的描述相当简明扼要.我可以找到电子书或pdf以获得详细信息吗?谢谢！

I have managed to fork and exec a different program from within my app. I'm currently working on how to wait until the process called from exec returns a result through a pipe or stdout. However, can I have a group of processes using a single fork, or do I have to fork many times and call the same program again? Can I get a PID for each different process ? I want my app to call the same program I'm currently calling many times but with different parameters: I want a group of 8 processes of the same program running and returning results via pipes. Can someone please point me to the right direction please ? I've gone through the linux.die man pages, but they are quite spartan and cryptic in their description. Is there an ebook or pdf I can find for detailed information ? Thank you!

pid_t pID = fork();
 if (pID == 0){
  int proc = execl(BOLDAGENT,BOLDAGENT,"-u","2","-c","walkevo.xml",NULL);
  std::cout << strerror(errno) << std::endl;
}

例如，如何通过PID控制哪个子项(根据参数xml文件)获得了哪个结果(通过管道或stdout)，并因此采取相应措施?我是否必须将子进程封装在一个对象中并从该对象开始工作，还是可以将它们完全分组?

For example, how can I control by PID which child (according to the parameter xml file) has obtained which result (by pipe or stdout), and thus act accordingly? Do I have to encapsulate children processes in an object, and work from there, or can I group them altogether?

推荐答案

一个Fork syscall仅创建一个新进程(一个PID).您应该组织一些数据结构(例如，pids数组，管道的父级末端数组等)，从主程序执行8 fork(每个孩子都会做exec)，然后等待孩子.

One Fork syscall make only one new process (one PID). You should organize some data structures (e.g. array of pids, array of parent's ends of pipes, etc), do 8 fork from main program (every child will do exec) and then wait for childs.

在每个fork()之后，它将返回您的孩子的PID.您可以存储以下pid和相关信息:

After each fork() it will return you a PID of child. You can store this pid and associated information like this:

#define MAX_CHILD=8
pid_t pids[MAX_CHILD];
int pipe_fd[MAX_CHILD];
for(int child=0;child<MAX_CHILD;child++) {
 int pipe[2];
 /* create a pipe; save one of pipe fd to the pipe_fd[child] */
 int ret;
 ret = fork();
 if(ret) { /* parent */ 
  /* close alien half of pipe */
  pids[child] = ret; /* save the pid */
 } else { /* child */
  /* close alien half of pipe */
  /* We are child #child, exec needed program */
  exec(...);
  /* here can be no more code in the child, as `exec` will not return if there is no error! */
 }
} 

/* there you can do a `select` to wait data from several pipes; select will give you number of fd with data waiting, you can find a pid from two arrays */

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