Forking and Waiting

Question

I am trying to create a fan of processes via forking. I want 1 process to be the base of the fan, and all other processes to fork from the base(all processes have the same parent, P1 is parent to P2, P3, P4, ...).

I have gotten this part down just fine. My real problem lies with waiting for the parent process(I think) to finish making children. Here is my code below:

//Create fan of processes
#include <iostream>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>

using namespace std;

int main()
{
  pid_t pid;
  cout << "Top Parent: " << getpid() << endl;
  for ( int i = 0; i < 9; ++i ) {
    pid = fork();
    if ( pid ) { //parent process
        continue;
    } else if ( pid == 0 ) {
        cout << "Child: (" << getpid() << ") of Parent: (" << getppid() << ")" << endl;
        break;
    } else {
        cout << "fork error" << endl;
        exit( 1 );
    }
  }
}

Guess I need some help on getting the output to behave itself as this is what it looks like:

Top Parent: 6576
Child: (6577) of Parent: (6576)
Child: (6581) of Parent: (6576)
Child: (6583) of Parent: (6576)
Child: (6579) of Parent: (1)
[remoteuser@server folder]$ Child: (6585) of Parent: (1)
Child: (6584) of Parent: (1)
Child: (6582) of Parent: (1)
Child: (6580) of Parent: (1)
Child: (6578) of Parent: (1)

possible duplicate of [getpid and getppid returns two different values](http://stackoverflow.com/questions/15183427/getpid-and-getppid-returns-two-different-values) — Jackson, Jan 20 '14 at 12:29
Your fork error detection will never trigger, because pid_t == -1 is caught by the `if (pid) { ...` clause. — hmn, Jan 20 '14 at 12:54
This is not really a duplicate of 'getpid and getppid returns two different values'. — Jonathan Leffler, Apr 08 '14 at 03:44

score 1 · Accepted Answer · answered Jan 20 '14 at 12:36

You should wait until all the child completes their tasks put following code in parent side.

   printf("Parent process started.n");
        if ((pid = wait(&status)) == -1)
                                     /* Wait for child process.      */                                   */
           perror("wait error");
        else {                       /* Check status.                */
           if (WIFSIGNALED(status) != 0)
              printf("Child process ended because of signal %d.n",
                      WTERMSIG(status));
           else if (WIFEXITED(status) != 0)
              printf("Child process ended normally; status = %d.n",
                      WEXITSTATUS(status));
           else
              printf("Child process did not end normally.n");
        }
        printf("Parent process ended.n");

Yeah I added the wait command into the parent if bracket and all is well, following @Developer SuRu's advice. Since I don;t think you can select a comment for best answer I will choose yours since it basically contains the same idea. — FailedFace, Jan 20 '14 at 12:42

Forking and Waiting

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