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From Clinton Gormley <cl...@traveljury.com >
Subject Re: mod_perl implementation possibility
Date Fri, 16 Mar 2007 09:27:34 GMT
> we are exploring the idea of writing medium to large
> Perl apps in the future which will require mod_perl.
> the current environment is apache 1.3.  having read
> modperl's doc and i am concerned about running
> multiple unrelated mod_perl apps on one server, such
> as 2 or 3 medium Perl apps. ( issue like database
> handler pollution etc which i know little about )
> 

The only place where you would have an issue with running multiple
applications within one server (even if distributed across virtual
servers) is where :
 - you have a common module that is used by more than one application
 - that module has the concept of a single set of configuration data
   rather than a per-application set

Not very clear, so let me give an example.

If, for example, you were to have a module called My::Template, that is
used by 5 different applications.

My::Template stores the path to the templates in the package wide
variable $template_path.

As each application sets its own template_path, it overrides the setting
from the application before.

The ways to avoid this are:
 * you pass the template path in to My::Template every time you call it

      process_template ($template_path, $template_name, $data)

 * you create a My::Template object which, amongst other things, has 
   the template path as a property

     $t = My::Template->new();
     $t->template_path($path);
     $t->process_template($template,$data);

 * for classes which inherit from My::Template, instead of using a
   scalar $template_path, you use a hash, which has the class of the  
   calling object as the key, and that classes template path as the
   value

     package My::Template;

     my %Template_Path;

     sub template_path {
         my $self = shift;
         my $class = ref $self || $self;
         if (@_) {
            my $path = shift;
            $Template_Path{$class} = $path};
         }
         return $Template_Path{$class}
    }


Another example of things with global effects is the current working
directory.  CWD is global, and thus you cannot rely on it staying the
same.  The safest way to handle this is to just use absolute filenames.

hth

Clint


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