Need explanation pcnt_fork()

Question

I am new to pcnt_fork,

<?php
  $pid = pcntl_fork();
  echo $pid;
  if($pid) {
  // parent process runs what is here
  echo "-parent\n";
   }
  else {
  // child process runs what is here
  echo "-child\n";
  } ?>

ouptut : 25347-parent 0-child

my question is , here $pid will be the process id of the child process i.e 25347 right? then it should echo only parent then why its also giving 0-child as a output...can anyone explain

Answer 1

This is what the state looks like after a fork operation:

           fork()
      +------+-----+
    child    |   parent
-------------+------------
> echo $pid  | > echo $pid
0            | 4650

Answer 2

pcntl-fork (just like fork) forks a child but it doesn't closes the parent.

In the end you have 2 running processes, the parent and the child.

The 2 lines of print that you are receiving come from 2 different processes: the parent that has received the pid of the child and the child itself.

Answer 3

On success, the PID of the child process is returned in the parent's thread of execution, and a 0 is returned in the child's thread of execution. On failure, a -1 will be returned in the parent's context, no child process will be created, and a PHP error is raised.