The "forks" pragma allows a developer to use threads without having to
have a threaded perl, or to even run 5.8.0 or higher. There were a number
of goals that I am trying to reach with this implementation.

The standard Perl 5.8.0 threads implementation is very memory consuming,
which makes it basically impossible to use in a production environment,
particularly with mod_perl and Apache. Because of the use of the standard
Unix fork() capabilities, most operating systems will be able to use the
Copy-On-Write (COW) memory sharing capabilities (whereas with the standard
Perl 5.8.0 threads implementation, this is thwarted by the Perl interpreter
cloning process that is used to create threads). The memory savings have
been confirmed.

You should be able to run threaded applications unchanged by simply making
sure that the "forks" and "forks::shared" modules are loaded,
e.g. by specifying them on the command line.

WWW: https://metacpan.org/release/forks