Sure. The perl documentation, for example: http://perldoc.perl.org/threads.html
The "interpreter-based threads" provided by Perl are not the fast, lightweight system for multitasking that one might expect or hope for. Threads are implemented in a way that make them easy to misuse. Few people know how to use them correctly or will be able to provide help. The use of interpreter-based threads in perl is officially discouraged.
And it seems like most of the posts or suggestions to use threads (that I've come across) are often countered saying that threads shouldn't be used, are heavier, more confusing, etc. If you'd like references, I can go pull some up from links I've saved.