What's the go with the GC these days?

[Steven Schveighoffer]

On 1/5/19 6:12 PM, Neia Neutuladh wrote:
> On Sat, 05 Jan 2019 14:05:19 -0800, Manu wrote:
>> Is progress possible, or is the hard reality that the language is just
>> designed such to be resistant to a quality GC, while the ecosystem sadly
>> tends to rely on it?
> 
> Three things about D make it harder to make a good GC for it:
> * unaligned pointers

Unaligned pointers are not scanned, and so this is not a problem. As far 
as the GC is concerned, they aren't pointers.

Perhaps you meant interior pointers?

> * unions

Unions and void * (or essentially untyped blocks) are the biggest 
problems. But depending on what we want to implement, we may have 
solutions for that.

It's difficult to paint with broad brushes here. There are certain 
problems that prevent certain solutions. But, for instance, a precise GC 
is getting traction as we speak: https://github.com/dlang/druntime/pull/2418

But precise GC is not necessarily better performing. And it's still 
"stop-the-world".

I think the biggest improvement for D's GC could be the thread-local 
pools (and avoid stop-the-world for those), but since casting shared and 
local data around is valid, I don't know how it can be implemented 
without language changes.

There are always extra heuristics and algorithmic improvements that 
people can analyze in the current GC as well.

-Steve