castaway has asked for the wisdom of the Perl Monks concerning the following question:

Hi people,
I'm writing a program in which users/developers can write their own 'plugins' as perl modules, and load them at runtime, now I'm trying to figure out how to make it possible to unload/reload changed modules without restarting the program.

After some playing around I came up with the following:
Load module using:

$modname = "Blah::Module";
eval "require $modname";

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Reload module using:
delete $INC{'Blah/Module.pm'};
eval "no warnings; require $modname";

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(To ignore the 'Subrouting redefined' warnings)

Anyone have any comments or better ideas?
Casty

Replies are listed 'Best First'.
Re: Reloading changed modules
by larsen (Parson) on Dec 21, 2002 at 17:19 UTC
    Apache::Reload module seems to apply the same technique. Here a snippet: 
            if ($mtime > $Stat{$file}) {
            delete $INC{$key};
 #           warn "Reloading $key\n";
            if (my $symref = $UndefFields{$key}) {
#                warn "undeffing fields\n";
                no strict 'refs';
                undef %{$symref};
            }
            require $key;
            warn("Apache::Reload: process $$ reloading $key\n")
                    if $DEBUG;
        }
        $Stat{$file} = $mtime;

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    The same technique, except that it copes with your "${package}::FIELDS" (which $symref in the snippet above is a reference to).

    For further info about %FIELDS, you can check the fields pragma man page (but check 5.8.0 perldelta about the deprecation of 5.6.1 pseudohashes' "user visible" implementation).

    Update: Clarified final note.

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      Thanks, I'll take a look.
      I should have tested better before, it seems my eval "no warnings; require $modname"; does not suppress the 'Subroutine redefined' warnings, any idea why?
      Casty
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        The module doesn't have 'use warnings;' in it does it? I've used the exact same technique to reload modules except for backwards compatibility I used 'local($^W) = 0;' to supress 'Subroutine redefined'.
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Re: Reloading changed modules
by gjb (Vicar) on Dec 21, 2002 at 23:29 UTC

    You may want to have a look at Term::ShellKit, it allows to load/reload modules on the fly and to evaluate Perl expressions.

    Hope this helps, -gjb-

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