Re^2: Variable will not stay shared in a sporadically crashing CGI

Apache resp. mod_perl is wrapping your CGI script in a subroutine to repeatedly call it.

This is the right explanation, but maybe the meaning is not completely clear. When you use Apache::Registry to run your script, it literally adds a set of brackets around your script and makes the whole thing into a sub, kind of like this:

sub handler {
   #!/usr/bin/perl
   use strict;
   use warnings;
   use CGI;
   my $cgi = new CGI;
   print_document_header();
   sub print_document_header {
      print $cgi->header( -type => 'text/html' ), "\n";
   }
}
[download]

Your workaround of explicitly passing around the variable is a good one in my opinion.

I completely agree, but if you're allergic to good programming practice you can just use our $cgi instead of my $cgi.

Comment on Re^2: Variable will not stay shared in a sporadically crashing CGI Download Code

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Re^3: Variable will not stay shared in a sporadically crashing CGI by haukex (Archbishop) on Oct 02, 2017 at 13:38 UTC
you can just use `our $cgi` instead of `my $cgi` Locutus: Please, avoid globals - the "best" way to do it is to pass `$cgi` as an argument to the subroutines.	[reply] [d/l] [select]
Re^4: Variable will not stay shared in a sporadically crashing CGI by LanX (Saint) on Oct 02, 2017 at 14:02 UTC
I'd say the problem is inter-mixing lexicals `my $cgi` with package symbols like named subs like `sub print_document` Changing to lexicals holding anonymous sub refs `my $print_document = sub {}` would solve the OP'S problem too. Having persistent shared globals can be a desired effect. (Initialization overhead, communication channel) Cheers Rolf _{(addicted to the Perl Programming Language and ☆☆☆☆ :) Je suis Charlie!}	[reply] [d/l] [select]
Re^4: Variable will not stay shared in a sporadically crashing CGI by Anonymous Monk on Oct 02, 2017 at 13:48 UTC
This is getting a bit off-topic, but some globals are ok. Novice programmers don't always know when they're safe and when they aren't, and they're often too timid to change a global to a local when it really needs to be done. That's why we advise people not to use globals at all. But CGI is probably safe as a global, because there's no reason to have two of them in your program.	[reply]
Re^5: Variable will not stay shared in a sporadically crashing CGI by haukex (Archbishop) on Oct 02, 2017 at 13:53 UTC
But CGI is probably safe as a global, because there's no reason to have two of them in your program. I absolutely agree with the general comment about some globals being ok if the coder knows what they are doing - but we are talking about mod_perl here, better to play it safe, and lexicals are arguably safer* in this case. * Update: "safer" not in the sense of security, but in less chances for things to go wrong.	[reply]