D Language 2.0

[Craig Black]

> If you do this and use this style for a significant percentage (well, more 
> than 10-15% of it, unless it's less than 5000 lines long) of your whole 
> program, then you are using C++ in D, and I think it's better for you to 
> avoid using D, and to use C++ or C or asm :-)

No I think that even using a limited subset of D would be quite liberating 
when compared with the hoops I have to jump through in my C++ code.  The new 
C++ standard will help some, but C++ isn't evolving fast enough.

> You can try to write D programs that are faster than the C++ ones, 
> instead. +-20% performance difference is not that important, you can aim 
> to a higher difference.

I always aim for high performance, but it may prove a challenge with D 
compiler/technology in its current state.  I know this is improving and will 
continue to do so.

> Try to use a more custom allocator, like pools, arenas, and so on, they 
> can be much better than nedmalloc. I have seen programs get about twice 
> faster doing this.

The main thing that I do on the memory side is to try to keep my memory use 
compact and contiguous, which is why I use arrays so much.

>>I use dynamic arrays quite a lot, and if I switched all of these to use 
>>D's built-in GC-based arrays, I think I would see a tremendous performance 
>>drop.<
>
> I am a bit suspicious of this. GC scans can slow down a little, but I'm 
> not seeing this as a big problem so far. You can test and benchmark some 
> of your theories. A problem I've seen is caused by the not precise nature 
> of the GC, wrong pointers keeping dead things alive.

One thing that I noticed while benchmarking is that when I remove the call 
to nedfree in my overloaded delete operator, application performance suffers 
by 17%.  You might expect this to increase performance if memory is never 
being freed.  Instead what happens is that locality of reference suffers. 
Thus, if D's GC never ran a single collection cycle, it would still be 17% 
slower than nedmalloc.  A moving GC would help this situation, but that's 
not the case with D.

Thanks for the pointers!

-Craig