#!/usr/bin/perl

=head1 NAME

child_to_parent_ipc_demo - child process reports on it's status to the parent

=head1 SYNOPSIS

  child_to_parent_ipc_demo

=head1 DESCRIPTION

A demonstration of a technique of spinning off a child process
which can report on it's progress back to the parent process,
while letting the parent go off and do some other things.

=cut

use warnings;
use strict;
# $|=1;

our $VERSION = 0.01;

use IO::Handle;  # brings in autoflush and blocking

# first set up a bi-directional pipe, 
# (will later close one direction)
my ($reader, $writer);
pipe $reader, $writer;
$writer->autoflush(1);  # still needed, even with modern perls
$reader->blocking(0);   # keeps reads from hanging

my $pid;
if ($pid = fork) {
  # this is parent code
  close $writer;

  print "Parent $$ is hearing from child $pid:\n";

  while (1) {
    my $status = '';
    $status = <$reader>; # magic "blocking(0)" keeps 
                         # this from blocking
    if ( defined( $status ) and ( $status =~ m{ ^ \d+ $ }xms ) ){
      # recieved an update child process status
      chomp( $status );
      print "\n$status% ";
      if ( $status >= 90 ) {
        close $reader;
        print "\n";
        exit;
      }
    } else {
      # can continue doing stuff here while child is running
      print ".";
      sleep 1;
    }
  }
} else {
  # this is child code
  die "cannot fork: $!" unless defined $pid;
  close $reader;

  # child code that takes awhile, but reports on it's status
  for my $i (1..10) {
    # the child takes a varying amount of time
    my $pause = int( rand(4) + .5 );
    sleep $pause;
    my $status = $i * 10;
    print $writer "$status\n";
  }

  close $writer;   # i/o doesn't go through until closed,
                   # *unless* autoflush is set to 1
  exit;
}

__END__


=head1 SEE ALSO

L<perlipc>

The Perl Cookbook, 2nd ed.
  Chapter 16 (interprocess communication)
  Chapter 7 (non-blocking i/o)

=head1 AUTHOR

Joseph Brenner, E<lt>doom@kzsu.stanford.eduE<gt>

=head1 COPYRIGHT AND LICENSE

Copyright (C) 2008 by Joseph Brenner

This program is free software; you can redistribute it and/or modify
it under the same terms as Perl itself, either Perl version 5.8.2 or,
at your option, any later version of Perl 5 you may have available.

=head1 BUGS

None reported... yet.

=cut