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module LineChunks
(
chunkedReadWith
) where
import Control.Exception (bracket, finally)
import Control.Monad (forM, liftM)
import Control.Parallel.Strategies (NFData, rdeepseq)
import Data.Int (Int64)
import qualified Data.ByteString.Lazy.Char8 as LB
import GHC.Conc (numCapabilities)
import System.IO
data ChunkSpec = CS {
chunkOffset :: !Int64
, chunkLength :: !Int64
} deriving (Eq, Show)
withChunks :: (NFData a) =>
(FilePath -> IO [ChunkSpec])
-> ([LB.ByteString] -> a)
-> FilePath
-> IO a
withChunks chunkFunc process path = do
(chunks, handles) <- chunkedRead chunkFunc path
let r = process chunks
(rdeepseq r `seq` return r) `finally` mapM_ hClose handles
chunkedReadWith :: (NFData a) =>
([LB.ByteString] -> a) -> FilePath -> IO a
chunkedReadWith func path =
withChunks (lineChunks (numCapabilities * 4)) func path
chunkedRead :: (FilePath -> IO [ChunkSpec])
-> FilePath
-> IO ([LB.ByteString], [Handle])
chunkedRead chunkFunc path = do
chunks <- chunkFunc path
liftM unzip . forM chunks $ \spec -> do
h <- openFile path ReadMode
hSeek h AbsoluteSeek (fromIntegral (chunkOffset spec))
chunk <- LB.take (chunkLength spec) `liftM` LB.hGetContents h
return (chunk, h)
lineChunks :: Int -> FilePath -> IO [ChunkSpec]
lineChunks numChunks path = do
bracket (openFile path ReadMode) hClose $ \h -> do
totalSize <- fromIntegral `liftM` hFileSize h
let chunkSize = totalSize `div` fromIntegral numChunks
findChunks offset = do
let newOffset = offset + chunkSize
hSeek h AbsoluteSeek (fromIntegral newOffset)
let findNewline off = do
eof <- hIsEOF h
if eof
then return [CS offset (totalSize - offset)]
else do
bytes <- LB.hGet h 4096
case LB.elemIndex '\n' bytes of
Just n -> do
chunks@(c:_) <- findChunks (off + n + 1)
let coff = chunkOffset c
return (CS offset (coff - offset):chunks)
Nothing -> findNewline (off + LB.length bytes)
findNewline newOffset
findChunks 0
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