Re: pmc_type

Paolo Molaro <lupus@xxxxxxxxxx> wrote:
> On 10/29/04 Leopold Toetsch wrote:

>> Well, we already got a nice method cache, which makes lookup a
>> vtable-like operation, i.e. an array lookup. But that's runtime only
>> (and it needs invalidation still). So actually just the first method
>> lookup is a hash operation.

> And where is it cached and how?

in src/objects.c:1077 ff. It's indexed by some bits of the method's
name address.

> From your description it seems it would look like:
>       vtable = $i->vtable;
>       code = vtable->method_lookup ("method"); // C function call
>       run_code (code);

The method_lookup doesn't have a vtable indirection. And having a direct
array lookup doesn't really scale. So the actual code is a bit more
complicated (and in no way optimized).

> Note that $i may be of different type for each loop iteration.

Sure.

> Even a cached lookup is going to be slower than a simple memory
> dereference. Of course this only matters if the lookup is
> actually a bottleneck of your function call speed.

Function calling is currently being changed. So I don't know yet.

>> > matter in parrot as long as bytecode values are as big as C ints:-)

[ more about op size ]

Well, that isn't an issue currently, AFAIK. More time consuming things
need optimizations first.

> BTW, in the computed goto code, make the array of address labels const:
> it helps reducing the rw working set at least when parrot is built as an
> executable.

Ah, yep. Thanks for the tip.

> lupus

leo