From: MenTaLguY <mental@...>
Date: 2008-01-08T05:29:30+09:00
Subject: Re: Fibers clear thread-specific data?

On Mon, 7 Jan 2008 09:34:35 +0900, "Tony Arcieri" <tony@clickcaster.com> wrote:
> Is this behavior intentional?
> 
>>> Thread.current[:foo] = :bar
> => :bar
>>> Fiber.new { p Thread.current[:foo] }.resume
> nil
> => nil
>>> Thread.current[:foo]
> => :bar

I think so -- a lot of existing code uses thread-specific variables to
simulate dynamic scoping, which would break if fibers did not each have
their own thread-specific data.

> Is there any way for a variable to be thread-specific but accessible to
> all fibers in that thread?

That's an interesting question.  At the moment, the best I can think of
is to have a (mutex-protected) weakhash of thread -> data pairs, with
lookups cached as thread-specific (really fiber-specific) data.

Of course, I've not looked closely at 1.9 Fibers -- it may be possible
to migrate them between threads, in which case things get harder.

I guess it would be best if we could have separate fiber-local and
thread-local data; the main issue is just backwards compatibility.

-mental