Item10601: Purging of templates causes failure of ICON macros

Publisher::publishUsingTemplate purges the templates after each topic is rendered:

    565         if ($Foswiki::Plugins::SESSION->can('templates') and
    566             $Foswiki::Plugins::SESSION->{templates} and
    567             ref $Foswiki::Plugins::SESSION->{templates} and
    568             $Foswiki::Plugins::SESSION->{templates}->can('finish') )
    569         {
    570             $Foswiki::Plugins::SESSION->{templates}->finish();
    571             undef $Foswiki::Plugins::SESSION->{templates};
    572         }

The comments preceding the code indicate this is to fix server load issues in generating the PublishPlugin summary output if there are lots of errors during the Publish process.

Unfortunately, this interacts poorly with an optimization in Foswiki/Macros/ICON.pm in the ICON subroutine which tries not to continually reload the icon templates:

    155     if ( !defined( $this->{_ICONSTEMPLATE} ) ) {
    156 
    157         #if we fail to load once, don't try again.
    158         $this->{_ICONSTEMPLATE} = $this->templates->readTemplate('icons');
    159     }

The problem is that when publishUsingTemplate purges the templates, when the ICON subroutine is next invoked it doesn't know it needs to reload the icon templates, assumes they're there, and fails.

(BTW, the comment in the ICON optimization code doesn't seem to match the current code base. If Templates::readTemplate fails it will throw an oops and you'll never traverse this code path again. Instead, this code ensures that if the template is successfully loaded it will never get loaded again.)

The following kludge fixes the problem by explicitly destroying the _ICONSTEMPLATE semaphore when purging the templates.

    565         if ($Foswiki::Plugins::SESSION->can('templates') and
    566             $Foswiki::Plugins::SESSION->{templates} and
    567             ref $Foswiki::Plugins::SESSION->{templates} and
    568             $Foswiki::Plugins::SESSION->{templates}->can('finish') )
    569         {
    570             $Foswiki::Plugins::SESSION->{templates}->finish();
    571             undef $Foswiki::Plugins::SESSION->{templates};
    572             delete $Foswiki::Plugins::SESSION->{_ICONSTEMPLATE};
    573         }

-- DiabJerius - 05 Apr 2011

This problem is also seen with the ImagePlugin, which also caches template information. On my site it seems the safest approach is to simply comment out the code which purges the templates.

-- DiabJerius - 05 Apr 2011

I agree. I have set a configuration var with this as the default state (no purge). Foswiki:Main.MichaelTempest can enable it if he still needs it.

-- CrawfordCurrie - 25 May 2011

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