Re: [Boost-users] Flyweight: wrapping shared_ptr

Subject: Re: [Boost-users] Flyweight: wrapping shared_ptr
From: Joaquin M Lopez Munoz (joaquin_at_[hidden])
Date: 2014-10-12 14:46:43

Akim Demaille <akim <at> lrde.epita.fr> writes:

> 
> Hi Joaquín,
> 
> The new bench is as follows:
> 
>   {
>     size_t n = 10 * 1000;
>     Exp exp = num(0);
>     for (unsigned j = 1; j <= n; ++j)
>       {
>         Exp e = bin('*',
>                     bin('+', num(j), num(j)),
>                     bin('+', num(j), num(j)));
>         Exp f = bin('/', e, e);  // <======== a fancy "1"
>         exp = bin('+', exp, f);  // <======== so this is ++exp
>       }
>     assert(exp->eval() == n);
>   }

I think you can make the test even more realistic: as it stands now,
the level of value redundancy is very low --for instance, each num
value is repeated only four times--, which is not the ideal setting
for Boost.Flyweight. If you change the creation of e to something like

        Exp e = bin('*',
                    bin('+', num(1+(j%m)), num(1+(j%m))),
                    bin('+', num(2+(j%m)), num(2+(j%m))));

for some constant m (in the range of 1000, for instance) then you
can modulate the level of redundancy (the lower m, the more duplicate
values): tuning m can tell you how Boost.Flyweight improves wrt the
shared_ptr case (which should not be affected by m at all). I bet
by having m sufficient low and n sufficiently high #7 can get to beat #1.
 
> which I ran on several implementations:
> 
> [...]
> 
> The results are:
> 
> ./1     0,02s user 0,00s system 93% cpu    0,031 total
> ./7     0,06s user 0,00s system 97% cpu    0,070 total
> ./9    46,19s user 0,09s system 99% cpu   46,424 total
> ./10  171,29s user 9,71s system 99% cpu 3:01,09  total
> ./11   17,25s user 0,04s system 99% cpu   17,296 total
> 

Well, seems like there's a clear winner here (ruling out #1, which
I understand from what you say it's not an acceptable alternative,
presumably because of memory limitations).

Joaquín M López Muñoz
Telefónica