Re: Interest in a cache class?

From: rogeeff (rogeeff_at_[hidden])
Date: 2002-03-11 17:55:19

--- In boost_at_y..., "David Abrahams" <david.abrahams_at_r...> wrote:
> 
> ----- Original Message -----
> From: "Rainer Deyke" <root_at_r...>
> To: <boost_at_y...>
> Sent: Monday, March 11, 2002 12:33 PM
> Subject: Re: [boost] Interest in a cache class?
> 
> 
> > ----- Original Message -----
> > From: "David Abrahams" <david.abrahams_at_r...>
> >
> >
> > > ----- Original Message -----
> > > From: "Rainer Deyke" <root_at_r...>
> > >
> > > > > > However, having lots of shared_ptrs
> > > > > > keeping the cached objects alive defeats the purpose of 
the
> > cache.
> > > > >
> > > > > Maybe your purpose. When I've needed a cache, I've needed 
some
> > way
> > > > to
> > > > > prevent certain objects from being flushed.
> > > >
> > > > Why?
> > >
> > > Because the objects were "currently in use" - essentially 
because
> > they
> > > were likely to be needed again soon,
> >
> > I remain unconvinced.  There is no semantic difference between 
keeping
> > the same object around and discarding it and reloading on demand.
> > There is a difference in performance, but the cache itself is 
probably
> > in a better position to judge when objects should be discarded 
than
> > the user.
> 
> It seems a bit perverse to design a cache around the idea that the 
user
> doesn't understand her performance needs as well as the cache 
designer.
> Once I'm using a cache, I'm already in the domain where I want 
control
> over low-level details that affect performance. If I didn't care 
about
> that, I'd just recompute the data each time I needed it.
> 
> -Dave

I am using manager algorithms (Policy) for this purposes. Every time 
I need to make a decision what/when to flush/load I call appropriate 
methods of manager algorithm class. You could apply something like 
this here.

Gennadiy.