Compare-and-swap semantics in GHC

Carter Schonwald carter.schonwald at
Thu Dec 5 08:48:44 UTC 2013

cas in ghc has sequential semantics.

i'm not sure if every use of it needs that semantics, if you identify
examples where weaker operations may suffice, please share!

On Thu, Dec 5, 2013 at 2:58 AM, KwangYul Seo <kwangyul.seo at> wrote:

> Hi,
> java.util.concurrent.atomic package provides two flavors of compare and
> set operations: compareAndSet and weakCompareAndSet. The latter does not
> create any happens-before orderings, so we can use it where no guarantees
> with respect to previous or subsequent reads and writes of any variables
> other than the target of the weakCompareAndSet are required.
> I'd like to ask if the compare-and-swap function provided by GHC runtime
> (cas() in includes/stg/SMP.h) is strong or weak. If it is strong, do all
> use cases of cas() require this semantics?
> Regards,
> Kwang Yul Seo
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