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Subj : Re: Can C++ local static objects be made thread safe?
To   : comp.programming.threads
From : gniccolai
Date : Thu Feb 17 2005 03:20 am

gottlobfrege@gmail.com wrote in message news:<1108573119.999831.204930@g14g2000cwa.googlegroups.com>...
> Giancarlo Niccolai wrote:
> 
> ...
> > as pthread_once does not need
> > to use a mutex, and usually (in well built implementations) it does
> > not. But there are other problems, that I won't discuss with you.
> ...
> > Gian.
> 
> Will you discuss it with me?  I've been looking at versions of 'once'
> lately (ie boost's and my own) and would be interested in any problems
> with pthread_once, as well as versions that don't use a mutex.  (Mine,
> under Windows, appears to only need a Critical Section and a few Atomic
> operations, which, I hope is slightly better than boost's version,
> which uses a global named mutex...)
> 

Yes. Pthread_once (and things with the same semantic) will execute a
certain code just once. So, in static initializer context, the first
thread passing on will begin to initialize the object; other threads
crossing the same code section will skip what pthread_once does and
will get the object; but the first thread may well not have fully
initialized it (or in case of a COFU thing, it may not even have it
placed in its final destination variable), so accesses to the object
may bang your program. I.e., a thread may wish to add an element at
the end of a list in the static initialized object, but the first
thread may have not been able to create the list yet.

Gian.

.

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