Parrot threads were featured on the perl advent calendar, day 11. Something cool about Perl 6 every day, in December.
See http://perl6advent.wordpress.com/2012/12/11/day-11-parrot-threads/.
Parrot always supported “threads”, i.e. concurrency models over the last years, but we identified various problems with the particular designs and were continuously improving them. In our case without changing the API too much, as the pdd25 concurrency spec is pretty high level, describing the various models parrot should support, and also pretty low-level in describing the two PMC’s which export the threads API, the Task and the Scheduler classes. ...