Shared and GC

[via Digitalmars-d-learn]

On Thursday, 15 January 2015 at 15:31:17 UTC, Peter Alexander 
wrote:
> On Thursday, 15 January 2015 at 15:24:55 UTC, Ola Fosheim 
> Grøstad wrote:
>> That would be nice, because then a precise garbage collector 
>> could choose between local collection scans and global 
>> collection scans.
>
> I think something like this is part of the plan, but shared 
> semantics are still up in the air.

That sounds like a very important aspect of a plan to get fast GC 
without completely changing the language and non-gc performance.

I've looked at bit at how to do a fast stop-the-thread GC. 
Estimates on what the hardware supports (bandwidth and cache 
performance) suggests that it is possible to get acceptable rates 
for not-densely-linked heaps with some tweaks to semantics:

- shared-awareness in new-expressions to support local collection

- removing class-destructors

- locating traceable pointers to the same cachelines in class 
instances (negative offsets is the easy solution)


Then you cn use a ache-optimized collector using batched 
non-caching queues with prefetching to get bitmaps that fits in 
1st level cache without wrecking the cache for other threads and 
having collection dominated by cache misses.