Subj : Re: Can C++ local static objects be made thread safe?
To   : comp.programming.threads
From : Marcin 'Qrczak' Kowalczyk
Date : Sat Feb 19 2005 01:49 pm

gniccolai@yahoo.com (Giancarlo Niccolai) writes:

> I can try to access any variable from any thread in any moment, in C,
> in C++, or in any language, and there's nothing in the C++ or posix
> standards preventing me from doing it.
>
> The fact that its initialization may be or may be not already complete
> is MINE problem, not the compiler's, not the standard's, but mine alone.

C++ standard explicitly says that this has undefined behavior, so you
have no right to complain to a C++ compiler vendor that the compiler
causes a deadlock in this case.

Indeed it's your problem if you rely on undefined behavior and your
program starts to misbehave in a different way. Other compilers may
follow GCC which in version 4 already makes static locals MT-safe.

It can be turned off, but not because it might not work (it doesn't
break correct programs): "Most users should leave this alone,
but embedded programmers may want to disable this by specifying
-fno-threadsafe-statics for a small savings in code size."

The internal API used by code generated by GCC is described here:
http://www.codesourcery.com/cxx-abi/abi.html#once-ctor

-- 
   __("<         Marcin Kowalczyk
   \__/       qrczak@knm.org.pl
    ^^     http://qrnik.knm.org.pl/~qrczak/

.