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List:       koffice-devel
Subject:    Re: [patch] koffice/libs/: port K3StaticDeleter to K_GLOBAL_STATIC
From:       Jaroslaw Staniek <js () iidea ! pl>
Date:       2008-08-27 10:30:48
Message-ID: 48B52CD8.4090909 () iidea ! pl
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Thomas Zander said the following, On 2008-08-27 08:09:
> On Wednesday 27. August 2008 00:56:48 Jaroslaw Staniek wrote:
>> Hi,
>> Being bored with the warnings, I've finally ported K3StaticDeleters to
>> K_GLOBAL_STATICs. Since K_GLOBAL_STATIC overloads 'operator type*', I've
>> merged ctors with private ::init() method if there's any, to make the
>> code even simpler.
>> All the statics like s_instance are no put within the private (but still
>> static) usage of K_GLOBAL_STATIC within the blocks of instance() static
>> methods. This is the way how K_GLOBAL_STATIC is used in kdelibs too (and,
>> what's good, in our apps like KSpread).
> 
> The reason I never did this is because as far as I understand it can't work 
> with K_GLOBAL_STATIC; hopefully I'm wrong.
> 
> The init and the constructor are separate for a good reason. The init 
> fetches all the plugins and constructs them. So calling init can take quite 
> some time.
> All the plugins do thing too, including calling another singleton. Which 
> will then create lots of plugins there. And those plugins may use our 
> singleton.  And you have a loop.

K3StaticDeleter does not protect us for this - do you accept that the 
singleton is accessed in somewhat uninitialized state (before init() ends)?

> Now, as far as I know a global-static only has a real pointer to it when the 
> constructor finishes (basic OO, you can't use an object until its 
> constructor finishes).  So if I call instance() *from* the constructor, 
> I've got a problem.
> 
> And we do call instance() from the constructor in our 3rd party plugins, so 
> we do need an init() method.

> If we can do that using K_GLOBAL_STATIC; great.  But I've been told by the 
> author that its not possible. 

So I propose to keep init() and go with K_GLOBAL_STATIC; which works just like 
the old static deleter in this case. Plus appropriate comments would be added 
on why we need init().

Example:

KoShapeRegistry* KoShapeRegistry::instance()
{
     K_GLOBAL_STATIC(KoShapeRegistry, s_singleton)
     if (!s_singleton->exists())
	s_singleton->init();
     return s_singleton;
}

OK?

-- 
regards / pozdrawiam, Jaroslaw Staniek
  Sponsored by OpenOffice Polska (http://www.openoffice.com.pl/en) to work on
  Kexi & KOffice (http://www.kexi.pl/en, http://www.koffice.org/kexi)
  KDE Libraries for MS Windows (http://windows.kde.org)
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