MT-safe string, part 1

[Benjamin Kosnik]

> Attached below are diffs for the essentials of MT-safe basic_string<>.

thanx daddyo

> What is missing is the #include and the configure script apparatus to 
> choose the right include file to declare (and define) the primitives
> used.  (The corresponding apparatus in Glibc refers to 
> sysdeps/*/atomicity.h.  For some reason the x86 (x >= 4) version of 
> that file, as posted here earlier, is not there.)

yeah we should probably pull in the sysdeps/(arch)/atomicity headers. 
They define primitives for alpha/arm/hppa/mips/powerpc/sparc. And 
variants. No sense duplicating code..

> Note that for most uses on Linux, just substituting different header 
> includes is _not_ sufficient.  Most distributions are built for a "386" 
> target, which lacks the appropriate instructions.  (SPARC-1 and HPPA, 
> I gather, also lack appropriate instructions, so MT on them will be 
> miserable.)  Linking an alternatively-compiled version of the library, 
> a common adaptation, wouldn't be enough, because these are inline 
> operations which affect non-library object files.

there are i386/i486/i586/i686/i786 dirs, but an atomicity only in i486. 
We can do it for i486 or above, forget about the rest.

or put in stubs, like sysdeps/generic

> If someone can point me at the right place to hack the apparatus in,
> and/or an example of similar things done, I can do more of the job.

the glibc stuff? you can look at the autoconf hackery in acinclude.m4, 
say GLIBCPP_CHECK_CTYPE. I'll look at this tomorrow.

-benjamin