Dear Fellow Monks,

please, have a look at the following quite minimalistic CGI program:

#!/usr/bin/perl
use strict;
use warnings;
use CGI;

my $cgi = new CGI;

print_document_header();
print_document();


######################################################################
sub print_document_header {
######################################################################
    print $cgi->header( -type => 'text/html' ), "\n";
}


######################################################################
sub print_document {
######################################################################
    print $cgi->start_html(
              -dtd     => '-//W3C//DTD HTML 4.01 Transitional//EN',
              -title   => 'Hello, world!',
          ), "\n",
          $cgi->p( 'Hello, world!' ), "\n",
          $cgi->end_html();
}
[download]

I have three questions regarding this program:

1. Whenever this program runs I get the warnings Variable "$cgi" will not stay shared referring to lines 15 and 22. Of course, I consulted perldiag in order to learn more about this kind of warning but - just like each of the other pages I found by searching the web for it - perldiag only talks about "an inner (nested) named subroutine ... referencing a lexical variable defined in an outer named subroutine". So where am I nesting named subroutines in my program? I only see two separate subroutines in a main program.
2. When running this CGI under Apache/2.2.31 (Unix), mod_perl/2.0.8, Perl/v5.10.1 I see it working as expected the first few times I reload the request but after some (varying) number of reloads it crashes with a segmentation fault! What's happening there?
3. By trial-and-error I found that it makes the program perfectly stable if I pass $cgi to the print_document_header subroutine as a parameter, i.e. calling print_document_header( $cgi ) with

   ######################################################################
   sub print_document_header {
   ######################################################################
       my $cgi = shift @_; 
       print $cgi->header( -type => 'text/html' ), "\n";
   }
   [download]

   Why is it sufficient to pass $cgi only to the subroutine which calls $cgi->header and simply use the "global" $cgi in any other subroutine?

Humble thanks for your adwise in advance!