Difference between __gshared and shared.

[Jonathan M Davis via Digitalmars-d]

On Wednesday, 8 July 2015 at 09:54:01 UTC, ketmar wrote:
> On Wed, 08 Jul 2015 09:43:38 +0000, wobbles wrote:
>
>> Ok, so we should prioritise using 'shared' over __gshared as 
>> much as possible. Good to know!
>
> only `shared` is PITA...

The primary advantage of shared is that it allows most everything 
to be thread-local.

Though arguably, shared _should_ be a bit of a pain, since its 
usage should normally be very restricted. But we do need to 
revisit shared and figure out what we want/need to do with it. 
Synchronized classes as described in TDPL were never even 
implemented (though I contest that they really make shared usable 
in any kind of sane way; I really don't see how you can do 
anything other than really basic stuff with shared without 
requiring that the programmer deal with the locks and casting 
properly on their own). So, more work needs to be done there even 
if it's figuring out what shared _isn't_ going to be doing.

Really though, one of the bigger problems is dealing with 
allocation and deallocation of shared objects and passing objects 
across threads, since we keep wanting to be able to do stuff like 
have thread-specific allocators, but the way shared currently 
works doesn't actually allow for it. :|

Regardless, while I would very much like to see shared properly 
ironed out, I'm _very_ grateful that thread-local is the default 
in D. It's just so much saner.

- Jonathan M Davis