Re: [boost] flyweight library?

From: JOAQUIN LOPEZ MU?Z (joaquin_at_[hidden])
Date: 2006-10-08 07:21:04

----- Mensaje original -----
De: Janek Kozicki <janek_listy_at_[hidden]>
Fecha: Domingo, Octubre 8, 2006 0:12 am
Asunto: Re: [boost] flyweight library?
Para: boost_at_[hidden]

> Joaquín M_ López Mu_oz said:     (by the date of Fri, 06 Oct 2006 
> 07:48:22 +0200)
> 
> > Janek Kozicki ha escrito:
> 2. a Typo in libs/flyweight/doc/tutorial/holders.html:
> 
> "For instance, flyweight&ltT> is equivalent to"
>                        ^^^

Thank you, will fix it.
 
> 3. am I right to think that:
> 
> flyweight<std::string,hashed_factory<>,global_holder<unsigned 
> char> >
> 
> will allow me to have 255 different strings, while
> 
> flyweight<std::string,hashed_factory<>,global_holder<unsigned 
> short> >
> 
> will allow me to have 65535 ?

Emm, no, that's not correct. The holder is used to maintain
a unique copy of the flyweight factory, its role is very
similar to that of a singleton. Nothing to do with controlling
the capacity of the factory.

> 
> 
> 4. have you ever thought about sample usage of flywieght to create 
> a new
> boost library: boost::flyweight_shared_ptr<T> ?
> 
> The problem it tries to solve is that on amd64 each pointer 
> consumes 64
> bits (8 bytes!), when people make a switch from 32bits to 64bits, 
this
> hurts badly. In my calculations memory usage grew from 700MB to 
1.3GB,
> and that actually makes a difference. (it's not possible to run
> calculations if some of the data must swap to disc...)
> 
> hmm... maybe this will actually work:
> 
> boost::flyweight<boost::shared_ptr<T> >
> 
> will it?

Well, the short answer is that flyweight won't gain you
nothing wrt to shared_ptr, since flyweight objects contain
a pointer (much like shared_ptr's) which is 8 bytes in 64bit
architectures.
The long answer is, given the flexibility that the
componentized nature of flyweight allows, it is possible to
devise a factory adaptor that limits the capacity of the
factory *and* let the flyweight object use internally a
handle value smaller in size than a pointer (an index of size
unsigned short, for instance). I will try to write something
along this line, I'll keep you informed.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo