Recipe 12.11 Speeding Up Module Loading with Autoloader

12.11.1 Problem

You want to use the AutoLoader module.

12.11.2 Solution

The easiest solution is to use the h2xs facility to create a directory and all the files you need. Here we assume you have your own directory, ~/perllib/, which contains your personal library modules.

% h2xs -Xn Sample
% cd Sample
% perl Makefile.PL LIB=~/perllib
% (edit Sample.pm)
% make install

12.11.3 Discussion

The AutoLoader addresses the same performance issues as the SelfLoader. It also provides stub functions that get replaced by real ones the first time they're called. But instead of looking for functions all in the same file, hidden below a _ _DATA_ _ marker, the AutoLoader expects to find the real definition for each function in its own file. If your Sample.pm module had two functions, foo and bar, then the AutoLoader would expect to find them in Sample/auto/foo.al and Sample/auto/bar.al, respectively. Modules employing the AutoLoader load faster than those using the SelfLoader, but at the cost of extra files, disk space, and complexity.

This setup sounds complicated. If you were doing it manually, it probably would be. Fortunately, h2xs helps out tremendously here. Besides creating a module directory with templates for your Sample.pm file and other files you need, it also generates a Makefile that uses the AutoSplit module to break your module's functions into little files, one function per file. The make install rule installs these so they will be found automatically. All you have to do is put the module functions down below an _ _END_ _ line (rather than a _ _DATA_ _ line as in SelfLoader) that h2xs already created.

As with the SelfLoader, it's easier to develop and test your module without the AutoLoader. Just comment out the _ _END_ _ line while developing it.

The same restrictions about invisibility of file lexicals that apply to modules using the SelfLoader also apply when using the AutoLoader, so using file lexicals to maintain private state doesn't work. If state is becoming that complex and significant an issue, consider writing an object module instead of a traditional one.

12.11.4 See Also

The documentation for the standard module AutoLoader; h2xs(1); Recipe 12.10