Adding atomic primops

[Carter Schonwald]

ryan, any thoughts on the (valid!) concern John Lato raises?

I know you mentioned fighting ghc optimizations when writing concurrent
code a while ago, and i believe I asked if you could document the issues
some time so we can all think about how to make the sitch easier, could you
share your thoughts?

AFAIK, there isn't a clear "this is the memory ordering rules" even in an
informal sense for ghc core / stg / cmm, and maybe we need to pin down some
"informal" guarantees we want to hold?

-Carter


On Sun, May 4, 2014 at 6:32 PM, John Lato <jwlato at gmail.com> wrote:

> Hello,
>
> IMHO I think the desire to include these features is leading to a slightly
> cavalier attitude towards reordering concerns.  Even assuming that the Cmm
> code generator doesn't reorder reads/writes around `CallishMachOp`, I don't
> see why this behavior should always be true, leading to possible future
> pain.  Also, it's possible that LLVM may decide to reorder memory accesses
> AIUI because the underlying LLVM variables won't be synchronized.
>
> In a nutshell, even though everything may work now I suspect it'll become
> an ill-specified mess in a few years time.  I don't have a ton of
> experience implementing these sorts of features in compilers though, so
> probably only worth a half cent.
>
> John L.
> On May 4, 2014 3:10 AM, "Johan Tibell" <johan.tibell at gmail.com> wrote:
>
>> Hi,
>>
>> I found myself needing atomic operations on basic, mutable numeric
>> values. I wrote a short design doc that I'd like feedback on:
>>
>> https://ghc.haskell.org/trac/ghc/wiki/AtomicPrimops
>>
>> I will try to implement these for 7.10.
>>
>> -- Johan
>>
>>
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