Re: [Haskell-cafe] scotty + aeson + ffi: optimising performance

5 Apr 2014

      sure, sorry should have done at the first place. Basically I have several
similar calls like one below. This one should be the heaviest one.

--scotty:
post "/setmoduletable" $ do
b <- body
let queryString = tableArrayInDataToJSON b
case queryString of
Nothing -> text $ "error parsing json! "
Just (ArrayDataIn tablename columnsCnt rowsCnt values) -> do
result <- liftIO $ FM.setmoduletable tablename columnsCnt rowsCnt values
let resultInt = fromIntegral $ result::Int
json $ ReturnIntData resultInt

--json conversions
tableArrayInDataToJSON :: L.ByteString -> Maybe ArrayDataIn
tableArrayInDataToJSON rawJson = retValue
where
json = decode rawJson :: Maybe ArrayDataIn
retValue = case json of
Nothing -> Nothing
Just a -> Just a

data ArrayDataIn = ArrayDataIn{
tablename :: !String
,columnscount :: Int
,rowscount :: Int
,values :: [Double]
}deriving (Show,Generic)

instance FromJSON ArrayDataIn
instance ToJSON ArrayDataIn

--ffi

foreign import stdcall safe "setmoduletable" c_setmoduletable :: CString ->
CInt -> Ptr CDouble -> CInt -> CInt -> CInt -> IO CInt

setmoduletable :: String -> Int -> Int -> [Double] -> IO CInt
setmoduletable param columns rows array = do
let cParamLength = fromIntegral $ length param ::CInt
    cColumns = fromIntegral $ columns ::CInt
    cRows = fromIntegral $ rows ::CInt
    cTable = [realToFrac x ::CDouble | x <- array]
    firstTimeStepAfterRestart = 0::CInt
cParam <- newCString param
cTablePtr <- newArray cTable
result <- c_setmoduletable cParam cParamLength cTablePtr cColumns cRows
firstTimeStepAfterRestart
free cTablePtr
free cParam
return result

On Sat, Apr 5, 2014 at 3:01 PM, John Wiegley  wrote:
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Miro Karpis  writes:
...
I tried to profile it but so far I can see that the bottleneck is Aeson
(please correct me if I'm wrong). Is there a way how to optimise it? The
data I'm sending via JSON are very small, so that can not be the problem.
Can you share any of your code with us?
John
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