Garbage collection in D

[BCS]

Hello Jarrett,

> On Tue, Jun 2, 2009 at 8:40 PM, Diwaker Gupta
> <diwaker at floatingsun.net> wrote:
> 
>> I've just started to play around with D, and I'm hoping someone can
>> clarify this. I wrote a very simple program that just allocates lots
>> of objects, in order to benchmark the garbage collector in D. For
>> comparison, I wrote the programs in C++, Java and D:
>> 
>> C++: http://gist.github.com/122708
>> 
>> Java: http://gist.github.com/122709
>> 
>> D: http://gist.github.com/121790
>> 
>> With an iteration count of 99999999, I get the following numbers:
>> JAVA:
>> 0:01.60 elapsed, 1.25 user, 0.28 system
>> C++:
>> 0:04.99 elapsed, 4.97 user, 0.00 system
>> D:
>> 0:25.28 elapsed, 25.22 user, 0.00 system
>> As you can see, D is abysmally slow compared to C++ and Java. This is
>> using the GNU gdc compiler. I'm hoping the community can give me some
>> insight on what is going on.
>> 
> D's GC is not nearly as well-developed as that of Java's, and its
> performance is not that stellar.  Sorry, but you are not the first to
> discover this by any stretch of the imagination.  (On a side note, I
> have a feeling you and bearophile will get on famously.)
> 
> Also, benchmarking a GC against manual memory management doesn't do
> much for you.  It's apples and oranges.  Though it is funny to see how
> badly Java beats C++ there.
> 

Java may be able to tell that the allocation never needs to be kept and is 
just reusing the same space on the stack. Heck it might even not be doing 
that as you can tell that the class only ever holds the same value as i so 
it might just be skipping the new all together.