More radical ideas about gc and reference counting

[Andrei Alexandrescu via Digitalmars-d]

On 4/30/14, 2:47 PM, John Colvin wrote:
> On Wednesday, 30 April 2014 at 20:57:26 UTC, Andrei Alexandrescu wrote:
>>> Finally, immutable is sharable accross thread. That mean, even if we
>>> bypass the type system, that RC must be atomic for immutable.
>>> As they
>>> convert automatically for co,st, that mean that all const code will be
>>> full of atomic increment/decrement. They are bad for the CPU, and cannot
>>> be optimized away.
>>
>> Good point. I see that as a problem, albeit a solvable one.
>
> How? Having lock; instructions implicitly appearing in normal looking
> slice code is unacceptable.

I'm thinking e.g. non-interlocked refcounts go like 1, 3, 5, ... and 
interlocked refcounts go like 2, 4, 6, ...

Then you do an unprotected read of the refcount. If it's odd, then it's 
impossible to having originated as an interlocked one. So proceed with 
simple increment. If it's even, do an interlocked increment.


Andrei