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

30 Dec 2012


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On Sun, Dec 30, 2012 at 3:39 PM, Vicente J. Botet Escriba
 wrote:
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Le 27/12/12 21:32, Felipe Magno de Almeida a écrit :
[snip]
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Also, I was expecting race conditions to be taken more seriously than
to wait for
bad behavior to appear. It is, afterall, a correctness issue.
You are right. the issue should be taken in account.
Does the following schema extracted from Boost.Units solve the issue or it
works only for POD types?
namespace detail {
template<bool>
struct xalloc_key_holder
{
     static int value;
     static bool initialized;
};
template<bool b>
int xalloc_key_holder<b>::value = 0;
template<bool b>
bool xalloc_key_holder<b>::initialized = 0;
struct xalloc_key_initializer_t
{
     xalloc_key_initializer_t()
     {
         if (!xalloc_key_holder<true>::initialized)
         {
             xalloc_key_holder<true>::value = std::ios_base::xalloc();
             xalloc_key_holder<true>::initialized = true;
         }
     }
};
namespace /**/ {
xalloc_key_initializer_t xalloc_key_initializer;
} // namespace
} // namespace detail
/// returns flags controlling output.
inline long get_flags(std::ios_base& ios, long mask)
{
     return(ios.iword(detail::xalloc_key_holder<true>::value) & mask);
}
I might not be knowledgeable enough to comment, but this seem a very
strange hack for the initialization order fiasco.
I don't know if it is a hack, but is been used in Boost in a lot of
Le 31/12/12 00:15, Felipe Magno de Almeida a écrit :
libraries.
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[snip]
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Boost.System will depend on Boost.Thread and Boost.Thread already depends
on
Boost.System.
I see. I rather they be interdependent than to have race conditions.
And I don't think call_once
requires boost.system. So at least cyclic includes could be avoided.
Yes, but this will mean to have two Boost.Thread libraries boost_thread
(with call_once) and boost_futures (which depend on Boost.System). I'm not
against this but this will mean a new breaking change.
If call_once were made header-only, there wouldn't be any breakage. IIUC.
I let you and Beman (Boost.System author) to continue this discussion. 
Please, create a Trac ticket for Boost.thread if some modifications are 
needed.

Best,
Vicente