For at least GHC 7.6, replace CMM code with straight C code about haskell-lockfree HOT 5 OPEN

I think this

stg_fetchAddByteArrayIntzh
/* MutableByteArray# s -> Int# -> Int# -> State# s -> (# State# s, Int# #) */
{
    W_ arr, p, ind, incr, h, len;
    arr  = R1; 
    ind  = R2;
    incr = R3;

    p = arr + SIZEOF_StgArrWords + WDS(ind);
    (h) = foreign "C" atomic_inc_with(incr, p) [];

    RET_N(h);
}

could be replaced by

foreign import ccall unsafe "atomic_inc_with" fetchAddByteArrayInt
    :: MutableByteArray# s -> Int -> Int -> IO Int

except I'm not quite sure about the s parameter to MBA#.

Relevant docs: https://www.haskell.org/ghc/docs/7.6.3/html/users_guide/ffi.html#idp56267600

from haskell-lockfree.

Figured it out: you also need to give the UnliftedFFITypes language pragma to be allowed to mention MBA# in the FFI import.

from haskell-lockfree.

How do you picture this working for CAS? It's a funky case because it currently returns a pair from the CMM primop:

stg_casMutVarzh ( gcptr mv, gcptr old, gcptr new )
{
    gcptr h;
    (h) = ccall cas(mv + SIZEOF_StgHeader + OFFSET_StgMutVar_var,
                          old, new);
    if (h != old) {
        return (1,h);
    } else {
        if (GET_INFO(mv) == stg_MUT_VAR_CLEAN_info) {
           ccall dirty_MUT_VAR(BaseReg "ptr", mv "ptr");
        }
        return (0,new);
    }

Assuming it is possible to do the GET_INFO/dirty bits in C, then there's just the issue of returning the two values efficiently. Could pass an output param for one and poke the pointer...

from haskell-lockfree.

Poking a pointer sounds like the way to go.

On Sun, Apr 13, 2014 at 3:57 AM, Ryan Newton [email protected]:

How do you picture this working for CAS? It's a funky case because it
currently returns a pair from the CMM primop:

stg_casMutVarzh ( gcptr mv, gcptr old, gcptr new ){
gcptr h;
(h) = ccall cas(mv + SIZEOF_StgHeader + OFFSET_StgMutVar_var,
old, new);
if (h != old) {
return (1,h);
} else {
if (GET_INFO(mv) == stg_MUT_VAR_CLEAN_info) {
ccall dirty_MUT_VAR(BaseReg "ptr", mv "ptr");
}
return (0,new);
}

Assuming it is possible to do the GET_INFO/dirty bits in C, then there's
just the issue of returning the two values efficiently. Could pass an
output param for one and poke the pointer...

Reply to this email directly or view it on GitHubhttps://github.com//issues/27#issuecomment-40298247
.

from haskell-lockfree.

Yeah, it's a write to memory rather than returning in registers but worth it to turn the double function call into a single one.

from haskell-lockfree.