Re: [boost] [review] Fast track review of Boost.Utility/Singleton begins today

From: Tobias Schwinger (tschwinger_at_[hidden])
Date: 2008-01-17 09:14:16

Martin Bonner wrote:
> From: Tobias Schwinger
>> Johan Nilsson wrote:
>>> Tobias Schwinger wrote:
>>>> Edson Tadeu wrote:
>>>>>   Does it support a single singleton across multiple DLL's? I.e.,
>>>>> singleton S is accessed the first time by DLL A (and is created),
>>>>> then it is accessed by DLL B. Does DLL B create a new instance of
>>>>> singleton S for it, or can it use the one created by DLL A as a
>>>>> truly global singleton?
>>>> Yes. See the documentation for details.
>>> Unless you have updated the documentation since the announcement, I
>>> think it would be a good idea to explain this in better detail. An
>>> 'implementation details' section would be a great addition to the
>>> document. 
>> OK, I'll take this as the "how does it work"-question :-).
>>
>> It's actually quite easy: The macros introduce a member function that
>> is defined in compiled code and used to access the Singleton. This 
>> way, all code to manage a Singleton's lifetime is in one place.
> 
> I haven't looked at the library, but I don't understand how that works
> on Windows.  Won't both DLLs have their own copy of the compiled code,
> and hence won't they both have their own copy of the singleton?

No. Only one DLL has the code and the other one calls it. That is, given 
an appropriate .def file or 'declspec'ing of the class and correct usage 
of the placement macros.

Regads,
Tobias