Things that keep D from evolving?

[Laeeth Isharc via Digitalmars-d-learn]

On Wednesday, 10 February 2016 at 20:21:22 UTC, Chris Wright 
wrote:
> On Wed, 10 Feb 2016 08:57:51 +0000, thedeemon wrote:
>
>> Currently (at least last time I checked) GC pauses the world, 
>> then does all the marking in one thread, then all the sweeping.
>
> Right.
>
>> We can do the
>> marking in several parallel threads (this is much harder to 
>> implement
>> but still doable),
>
> Parallel marking would not be a breaking change by any means. 
> No user code runs during GC collections, so we can do anything. 
> The major fly in the ointment is that creating threads normally 
> invokes the GC, since Thread is an object, and invoking the GC 
> during a collection isn't the best.
>
> This can be solved by preallocating several mark threads. Then 
> you just divide the stack and roots between those threads. 
> Moderately annoying sync issues
>
> This doesn't guarantee an even distribution of work. You can 
> solve that problem with a queue, though that requires locking.
>
> The main wrinkle is writing a bit to shared data structures, 
> which can be slow. On the other hand, in the mark phase, we're 
> only ever going to write the same value to each, so it doesn't 
> matter if GC thread A . I don't know how to tell the CPU that 
> it doesn't have to read back the memory before writing it.
>
>> and we can kick the sweeping out of stop-the-world
>> pause and do the sweeping lazily
>
> This would be a breaking change. Right now, your destructors 
> are guaranteed to run when no other code is running. You'd need 
> to introduce locks in a few places.
>
> I'm not saying this is a bad thing. I think people generally 
> wouldn't notice if we made this change. But some code would 
> break, so we'd have to stage that change.
>
> Anyway, I'm hacking up parallel mark phase to see how it would 
> work. I could use some GC benchmarks if anyone's got them lying 
> around.

https://github.com/D-Programming-Language/druntime/tree/master/benchmark/gcbench