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

From: David Abrahams (dave_at_[hidden])
Date: 2003-02-20 11:12:39

Gabriel Dos Reis <gdr_at_[hidden]> writes:

> David Abrahams <dave_at_[hidden]> writes:
>
> | Gabriel Dos Reis <gdr_at_[hidden]> writes:
> | 
> | > However, my point is that
> | >
> | >   * a class is closed: that is, by the time you put the closing brace,
> | >     the "offset" of the data member is a compile-time constant.
> | >
> | >   * the number of thread local variables is potentially unbounded,
> | >     meaning that, using your analogy, the offset of the corresponding
> | >     data-member is not known by the time the compiler finishes
> | >     processing a given translation unit.
> | 
> | OK... is that a problem?
>
> As I'm understanding the issue, yes.  I would love to be proved wrong.
>
> |  The address of a static global is not known
> | when the compiler finishes processing a given translation unit either.
>
> Sure the logical address is known.
>
> As opposed to the address of a variable with a TLS.

It has just one "logical address", which will turn out to correspond
to different physical addresses depending on the thread executing at
the time.  When the implementation handles it at compile-time, it uses
only the logical address.  At the compile-time/runtime boundary the
logical address is converted to a physical address by dereferencing
off the base TLS pointer.  This is just like a data member pointer.  I
still don't see a problem.

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