in reply to Which 'Perl6'? (And where?)
There's a distinction to be made between "discouraged" and "deprecated" with respect to the status of threading. I followed the discussions on the p5p mailing list out of curiosity. It appears that a few people grew tired of answering questions about threads (I think in IRC), and felt that threads' correct use was sufficiently complicated that it would be in everyone's best interest if newcomers were discouraged from using them. But it's my understanding that there's no intention of removing them entirely.
Here are a couple of related messages from P5P. The entire thread may be worth reading (at least I found it interesting).
I disagree with the strategy of "This is hard to use correctly so let's tell people not to use it." I think it's an over-reaction. If something is too difficult for some people to use correctly, that doesn't mean that it's of no value to those who have taken the time to learn how to use it properly. Most of the rest of Perl's documentation does a reasonable job of mentioning, "...this feature is deeply magic. Here be dragons." ...That sort of thing. There's nothing wrong with just documenting the complexities and suggesting that for many situations forking is easier to manage, rather than to strongly discourage the use.
A "Best Practice" might be to favor one approach over another in a general sense. But we all know that threads have specific uses that are not easily replaced with other technologies. For that reason, I think that "discouraged" is probably too strong.
But I do think to be fair one should recognize that they are not deprecated, and nobody is talking about removing threads from Perl.