Marc Lehmann has written Coro, a module that introduces coroutines and cooperative multitasking to Perl 5. I have toyed with it, as I find cooperative multitasking much more convenient than threading for most applications where operations can be made nonblocking for Perl.

He used the coroutines to drive a high throughput http daemon, but I found in the module versions I used, that Perl crashed unexpectedly from time to time without any indications as to what caused the crash.

But it sure is fun to program with coroutines, as creating a parallel version of LWP was really easy and nice with it.