Fork Process

From Rosetta Code

In this task, the goal is to spawn a new process which can run simultaneously with, and independently of, the original parent process.

Contents 1 C 2 Erlang 3 OCaml 4 Perl 5 Pop11 6 Python 7 Toka 8 UnixPipes

[edit] C

Works with: gcc

Library: POSIX

#include<stdio.h>
#include<unistd.h>

int main(void)
{
  pid_t pid;

  if((pid=fork())==0) {
    printf("This is new process\n");
  } else if(pid>0) {
    printf("This is the original process\n");
  } else {
    printf("ERROR: Something went wrong\n");
  }

  return 0;
}

[edit] Erlang

-module(fork).
-export([start/0]).

start() ->
    spawn(fork,child,[]),
    io:format("This is the original process~n").

child() ->
    io:format("This is the new process~n").

Then you can compile your code and execute it:

c(fork).
fork:start().

[edit] OCaml

#load "unix.cma";;
let pid = Unix.fork ();;
if pid > 0 then
  print_endline "This is the original process"
else
  print_endline "This is the new process";;

[edit] Perl

Works with: Perl version 5.x

In the child code, you may have to re-open database handles and such.

FORK:
if ($pid = fork()) {
    # parent code
} elsif (defined($pid)) {
    setsid; # tells apache to let go of this process and let it run solo
    # disconnect ourselves from input, output, and errors
    close(STDOUT);
    close(STDIN);
    close(STDERR);    
    # re-open to /dev/null to prevent irrelevant warn messages.
    open(STDOUT, '>/dev/null');
    open(STDIN, '>/dev/null');
    open(STDERR, '>>/home/virtual/logs/err.log');
    
    # child code
    
    exit; # important to exit
} elsif($! =~ /emporar/){
    warn '[' . localtime() . "] Failed to Fork - Will try again in 10 seconds.\n";
    sleep(10);
    goto FORK;
} else {
    warn '[' . localtime() . "] Unable to fork - $!";
    exit(0);
}

Obviously you could do a Fork in a lot less lines, but this code covers all the bases

[edit] Pop11

lvars ress;
if sys_fork(false) ->> ress then
   ;;; parent
   printf(ress, 'Child pid = %p\n');
else
   printf('In child\n');
endif;

[edit] Python

Works with: Python version 2.5

import os

pid = os.fork()
if pid > 0:
 # parent code
else:
 # child code

[edit] Toka

needs shell
getpid is-data PID
[ fork getpid PID = [ ." Child PID: " . cr ] [ ." In child\n" ] ifTrueFalse ] invoke

[edit] UnixPipes

Demonstrating a subshell getting forked, and running concurrently with the original process

(echo "Process 1" >&2 ;sleep 5; echo "1 done" ) | (echo "Process 2";cat;echo "2 done")