Hash class problem

[David Nolden]

Am Samstag, 20. September 2008 13:26:20 schrieb Andreas Pakulat:
> Hi,
>
> I've recently restarted my kdevelop/win32 efforts as I really need to
> get an IDE on that platform up and running (one that doesn't suck for
> C++) and I'm having a problem with duchain and its use of a hash class.
>
> As far as I understood QHash is too slow for the needs of duchain, is
> that right? If so: Has somebody with insight why QHash is so slow told
> TT? Obviously using QHash would be the best solution to the problem.

In test_duchain.cpp there is a test that also does some timing, and it comes 
to the conclusion that ext::hash_map is about 2x faster then QHash. Since the 
hashes in duchain are usually used in very tight loops, performance is 
important, so we don't use QHash there. QHash has some additional features 
like implicit sharing the we don't need at all in those places, and those 
features will probably prevent QHash from ever being as fast as 
ext::hash_map.

However now after I've removed some unused stuff from the cpp support, it 
seems like there is only one place left where hash_map is used without 
#ifdefs(and 2 places all in all), which is the cache in topducontext.cpp. 
Since most of the hashes in duchain are implemented in the item-repository, I 
think we won't need more hash_map than this, so you could just do the same 
#ifdefs like in duchainlock.cpp/duchainlock.h for the moment, and be fine.

Greetings, David