Re: [Boost-users] [system] local static and threading in C++03

Subject: Re: [Boost-users] [system] local static and threading in C++03
From: Vicente Botet (vicente.botet_at_[hidden])
Date: 2012-12-27 06:30:00

Felipe Magno de Almeida wrote
> Hello Vicente,
> 
> On Tue, Dec 25, 2012 at 6:28 PM, Vicente Botet <

> vicente.botet@

> > wrote:
>> Felipe Magno de Almeida wrote
>>> Hello,
> 
> [snip - source code]
> 
>>> But couldn't this make double construction/double free in C++03 systems
>>> if system_category is ran concurrently?
>>
>> Yes sure, this is always possible zith c++0·.
> 
> Not always possible. It is only possible for non-PODs. AFAIK.
> 
>> Do you see a problem with this implementation?
> 
> Since it has a race-condition, I would say I see a problem, yes.
> More so since it is not documented. 

Form a theoretical point of view yes. But in practice, which observable
problems could induce the double construction?
I would expect only one destruction, don`t you?

> AFAIK, the normal solution
> for this is to use call_once.
> 
> system_category const& create_system_category()
> {
>   system_category const category;
>   return category;
> }
> void init_system_category() { create_system_category(); }
> once_flag init_flag = BOOST_ONCE_INIT;
> 
> system_category const& get_system_category()
> {
>   boost::call_once(init_flag, &init_system_category);
>   return create_system_category();
> }

This approach would make both libraries interdependent.

Best,
Vicente

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