> On Jun 15, 2017, at 8:30 PM, Greg Parker <gpar...@apple.com> wrote:
>
> (You can do without a separate token if (1) your storage is two pointers or
> less in size, (2) your storage is sufficiently well-aligned that it does not
> cross cache line boundaries, (3) your uninitialized value is zero, and (4)
> your initialized value is not zero. If all of these are true then you can
> perform the same trick that swift-once and dispatch-once use on the once
> token, but apply it directly to the data instead. And if your data is a
> single pointer you can do it faster than dispatch-once on weakly-ordered
> platforms that are not Alpha.)
That’s a good point. I’ll switch the runtime’s TLS key initialization over to
that to save a load.
I assume the “two pointers or less” requirement is for an atomic store. And the
single pointer requirement is for a barrier-free load? Although couldn’t you
just atomically load two pointers?
-Andy
_______________________________________________
swift-dev mailing list
swift-dev@swift.org
https://lists.swift.org/mailman/listinfo/swift-dev
