#!/usr/bin/perl

use strict;
use warnings;

BEGIN {
   # Move to running in background.
   if (!@ARGV || $ARGV[0] ne '--nobkg') {
      $SIG{CHLD} = 'IGNORE';
      require IPC::Open3;
      IPC::Open3::open3(
         '<&STDIN',
         '>&STDOUT',
         '>&STDERR',
         $^X, $0, '--nobkg', @ARGV
      );
      exit;
   }
}

use threads;

sub my_sub {
   open(my $fh, '>', "$0.".threads->tid() )
      or die;
   print $fh 'text';
   sleep(10);
}

my $thread1 = new threads(\&my_sub);
my $thread2 = new threads(\&my_sub);

$_->join() for $thread1, $thread2;