Re: [boost] Re: Thread-Local Storage (TLS) and templates

From: David Abrahams (dave_at_[hidden])
Date: 2003-02-24 07:44:02

Gabriel Dos Reis <gdr_at_[hidden]> writes:

> | OK, whatever.  I guess I should've said that you can instantiate a
> | template on &k with sensible results.  Whether or not you want to call
> | it a constant is another semantic matter.  I'd call it a constant
> | which evaluates differently in different threads.  
>         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> And that isn't just a word-game as your message might imply it.

I never meant to imply that it's a word game, just that I'm only
willing to concede "not a constant-ness" for some very narrow
definition of the word "constant."  If you think of threads as being
truly concurrent, the value actually _is_ constant (just different in
different threads).

> | Within a single thread the value never changes.
>
> Like in
>
>    template<typename T>
>      struct X { };
>
>    int main()
>    {
>       const int i = 2003;
>       X<&i> x;
>    }
>
> ?

Not sure what you're getting at, since the code is invalid.  I'll
assume you meant X to take an int* parameter.

> In a given program run, &i won't change.  That is just in single
> thread mode.  Let's solve that first.

What is there to solve?  I'm not interested in making the above legal
(is calling main explicitly really disallowed?), but even if I were,
it doesn't seem closely related to the TLS problem.  I don't see how
solving your case would help (not that I understand what solving it
might mean).

> Extrapolating to a multi-thread mode isn't just changing a word.

BTW, aren't we wildly OT discussing this here?  Shouldn't it go to a
committee reflector or comp.std.c++?

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com