Create a chain of n sub processes

问题

In c++ create chain of n processes with n as input and the output of processes should be as parent1->child1(parent2)-->child2(parent3),by using recursive function im able to generate the output but unable to exit the loop i also need help in sending an input of n for which the loop should break.

below is my code:

#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/wait.h>

int foo(const char *whoami) {
    printf("I am a %s.  My pid is:%d  my ppid is %d\n", whoami, getpid(), getppid() );
    return 1;
}

int func() {
    pid_t pid=fork();
    if (pid==0) { /* only execute this if child */
        foo("child");
        pid_t pid=fork();
        if (pid==0) { /* only execute this if child */
            foo("child");
            func();
            exit(0);
        }
      }
      exit(0);
    }
    wait(0);  /* only the parent waits */
    return 0;     
}

int main(void){
    foo("parent");
    func(); 
    return 0;
}

回答1:

You can't exit the loop for a simple reason, and that is, you spawn child processes endless. Whenever you fork() a new process starts, then it forks again.

#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/wait.h>

int n=5;

int foo(const char *whoami) {
    printf("I am a %s.  My pid is:%d  my ppid is %d\n", whoami, getpid(), getppid() );
    return 1;
}

int func(int n) 
{
    if (n == 0)
    { 
        return 0;
    }
    int pid = fork(); 
    if (pid == -1) {
        exit(0);
    }
    if (pid==0) { 
        foo("child");
        n = n-1;
        func(n);
        exit(0);
    }
    else {
       wait(NULL);
    } 
    return 0;   
}


int main()
{
    func(n); 
    return 0;
}

gcc -std=c99 prog.c -o prog

./prog

OUTPUT:

I am a child. My pid is: 1159 my ppid is 1158
I am a child. My pid is: 1160 my ppid is 1159
I am a child. My pid is: 1161 my ppid is 1160
I am a child. My pid is: 1162 my ppid is 1161
I am a child. My pid is: 1163 my ppid is 1162

回答2:

From what you are saying i understand you are having the following problems:

1st. You are trying to send 'data' from one process to another

2nd. You are trying to find a way to stop your program from running.

Now for the first. If you want to do that and i understood it correctly, there are 2 ways to achieve that. One is the use of shared memory and the other is the use of pipelines. Shared memory is pretty obvious on what is doing. Pipes are taking the stdout of a process and redirecting it as a stdin in the next process.

Now you need a closure to your program. A child process is executed when it executes a command(exec) or when it is told so(with an IF statement for example and a return). You can create a statement of your liking, and when a child process meets your requirments then you can make it die(There is also a way to kill the parent process from the child process with the kill(pid, SIGKILL); command.

I didn't provide you with any code because it is unclear to me the exact nature of your problem. Hope my assuming led you to something!

来源：https://stackoverflow.com/questions/42291584/create-a-chain-of-n-sub-processes

标签

Linux

fork

systems-programming