DIP80: phobos additions

[Steven Schveighoffer via Digitalmars-d]

On 6/9/15 5:46 PM, Andrei Alexandrescu wrote:
> On 6/9/15 1:53 PM, Steven Schveighoffer wrote:
>> On 6/9/15 2:59 PM, Andrei Alexandrescu wrote:
>>> On 6/9/15 11:42 AM, Dennis Ritchie wrote:
>>>> "And finally `std.bigint` offers good (but not outstanding)
>>>> performance."
>>>
>>> BigInt should use reference counting. Its current approach to allocating
>>> new memory for everything is a liability. Could someone file a report
>>> for this please. -- Andrei
>>
>> Slightly OT, but this reminds me.
>>
>> RefCounted is not viable when using the GC, because any references on
>> the heap may race against stack-based references.
>
> How do you mean that?

If you add an instance of RefCounted to a GC-destructed type (either in 
an array, or as a member of a class), there is the potential that the GC 
will run the dtor of the RefCounted item in a different thread, opening 
up the possibility of races.

>> Can we make RefCounted use atomicInc and atomicDec? It will hurt
>> performance a bit, but the current state is not good.
>>
>> I spoke with Erik about this, as he was planning on using RefCounted,
>> but didn't know about the hairy issues with the GC.
>>
>> If we get to a point where we can have a thread-local GC, we can remove
>> the implementation detail of using atomic operations when possible.
>
> The obvious solution that comes to mind is adding a Flag!"interlocked".

Can you explain it further? It's not obvious to me.

-Steve