Re: [boost] call_once on win32

From: Anthony Williams (anthony_w.geo_at_[hidden])
Date: 2005-09-07 15:15:57

Alexander Terekhov <terekhov_at_[hidden]> writes:

> Anthony Williams wrote:
> [...]
>> I can understand what you're getting at with the derived class for dynamic
>> contexts, such as class members, but how are you envisioning the
>> call_once_reset function working? Would it take a specific once_flag as a
>> parameter, and reset it, as if it has never been called? 
>
> Yes. And also cleanup result stuff, if any. Pretty much the same notion 
> (reset() vs destroy() aside for moment) as with statically initialized 
> pthread primitives and corresponding _destroy() calls like 
> pthread_mutex_destroy() that can be used for "pedantic" cleanup of 
> statically initialized pthread objects at process termination to please 
> leak detectors (resources may be acquired dynamically on first use) or 
> whatnot.

Makes sense.

>> When would this be used, 
>
> That's up to the client. For example, in some module_fini().
>
>> and how would it help with static destruction?
>
> Static destruction of what?

Destruction of once_flags with static storage duration.

If we store the return value along with the once_flag, then we really ought to
destroy it properly, when the once_flag is destroyed. If a once_flag has
static storage duration, and has a non-trivial destructor that does cleanup,
then we have a classic singleton cleanup problem, as John Maddock pointed out
--- the order of static destruction can now be important.

Anthony
-- 
Anthony Williams
Software Developer
Just Software Solutions Ltd
http://www.justsoftwaresolutions.co.uk