Since Perl 5.8, thread programming has been available using a model called
interpreter threads which provides a new Perl interpreter for each thread,
and, by default, results in no data or state information being shared
between threads.
(Prior to Perl 5.8, 5005threads was available through the "Thread.pm" API.
This threading model has been deprecated, and was removed as of Perl 5.10.0.)
