atomic operations compared to c++

[Guillaume Piolat via Digitalmars-d]

On Tuesday, 13 June 2017 at 06:12:46 UTC, gzp wrote:
> But what about compare_exchange (CAS) ? In C++ one have to 
> provide Memory ordering for success and failure, but not in D.

I have some difficulty already to comprehend MemoryOrder.rel and 
MemoryOrder.acq
A cas with MemoryOrder.raw wouldn't be very useful.


> Does it mean, it is the strongest sequaential all the time, all 
> some explicit fence have to be provided.

It uses lock xchg 
https://github.com/dlang/druntime/blob/ce0f089fec56f7ff5b1df689f5c81256218e415b/src/core/atomic.d#L769

So no additional fences needed, it is already the strongest IIRC.

imho, if a CAS requires additional memory barriers, it's a bit 
useless..