Below you'll find an example of a multi-threaded Perl program as well as a forked Perl program.
Both seem to work fine. A disadvantage of threads is that Perl needs to be compiled with threads support.
Not all versions of Perl come with that by default.
A Perl Thread example
Perl Fork example
This examples fork 10 child processes.
It will wait for all childs to finish before exiting.
Output looks like:
PHP fork example
here's the same fork example implemented in PHP