externs and thread local storage

[Seongbae Park]

On 7/2/06, Gary Funck <gary@intrepid.com> wrote:
...
> More to the point, I think it is rather too bad that the
> extern has to have the __thread attribute at all, and would
> have hoped that the linker and OS could have collaborted to
> make this transparent, in the same way that data can arranged
> in separately linked sections without impacting the way
> the external references are written.  Thus, implementation
> is separated from interface.

TLS variable and non-TLS variable have totally different behaviors,
and hence they are not interchangeable.
Therefore, TLS aspect should not be made "transparent"
i.e. The programmer has to treat a global variable differently
depending on whether or not it is a TLS
and getting a different one when you expected otherwise will cause
subtle (well, actually not so suble, since it's likely to blow up in your face)
runtime problems.

>  I think the requirement to apply
> _thread to an extern should also be target specific.

As I said, you're welcome to implement a new option
(either a runtime option or a compile time configuration option)
that will allow mixing TLS vs non-TLS.
Whether or not it should be enabled for a particular platform
should be a matter of discussion, and whether or not that patch will be
accepted in the mainline will be yet another.

Because of the reasons I said above, I think it's a bad idea in general
and I'll oppose to it for any of platforms I care about.
-- 
#pragma ident "Seongbae Park, compiler, http://seongbae.blogspot.com"