use forks;    #ALWAYS LOAD AS FIRST MODULE, if possible
use warnings;

# a bunch more code that never mentions "use threads;"

##</code><code>##

# Use forks as a drop-in replacement for an ithreads application
perl -Mforks -Mforks::shared threadapplication

##</code><code>##

perl -Mforks  script.pl
perl -Mforks -Mforks::shared  script.pl