Discussion on Go and D

[Sean Kelly]

On Apr 7, 2012, at 9:45 AM, Rainer Schuetze <r.sagitario at gmx.de> wrote:

> 
> 
> On 4/6/2012 6:20 PM, deadalnix wrote:
>> Le 06/04/2012 18:07, Andrei Alexandrescu a écrit :
>>> A few more samples of people's perception of the two languages:
>>> 
>>> http://news.ycombinator.com/item?id=3805302
>>> 
>>> 
>>> Andrei
>> 
>> I did some measurement on that point for D lately :
>> http://www.deadalnix.me/2012/03/05/impact-of-64bits-vs-32bits-when-using-non-precise-gc/
>> 
> 
> I studied the GC a bit more and noticed a possible issue:
> 
> - memory allocations are aligned up to a power of 2 <= page size
> - the memory area beyond the actually requested size is left untouched when allocating
> - when the memory is collected, it is also untouched
> - the marking of references during collection does not know the requested size, so it scans the full memory block
> 
> Result: When a collected memory block is reused by a smaller allocation, there might still be false pointers in the unused area.
> 
> When I clear this data, my first impression is that it has improved the situation, but not enough. I'll have to create some non-interactive test to verify.

The unused area is typically zeroed out on allocation. Check GC.mallocNoSync.