[GHC] #8972: Investigate adding fast compare-and-swap Int type/primops

[GHC]

#8972: Investigate adding fast compare-and-swap Int type/primops
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        Reporter:  tibbe             |            Owner:  tibbe
            Type:  feature request   |           Status:  new
        Priority:  normal            |        Milestone:
       Component:  Compiler          |          Version:  7.9
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:  8157, 7883
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Comment (by rrnewton):

 Update: I confirmed that I get the exact same time for
 "Data.Atomics.Counter' (atomic-primops) as I do for Johan (tibbe)'s
 counter.c version of the benchmark here.

 Johan and I talked about this and it seems like the obvious way to improve
 performance on this is inline primops for the fetch-and-add (#7883).  We
 confirmed that the MutableByteArray# used by Data.Atomics.Counter is a
 single contiguous heap object, so the only advantage of a dedicated
 mutable reference type would be to save the word representing the length.

 More, generally, I wonder if we can have a user facing interface that
 makes mutable unboxed data more pleasant.  Unboxed vectors are nice, but
 there's nothing like an (IORef (# Int#, Int# #)), for example.  Even
 though with double-word CAS we could support some interesting data
 types...

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8972#comment:4>
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