src/Streamly/Internal/System/IO.hs · streamly

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streamly/src/Streamly/Internal/System/IO.hs

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1{-# LANGUAGE UnboxedTuples #-}

3-- |

4-- Module : Streamly.Internal.System.IO

6-- License : BSD-3-Clause

7-- Maintainer : streamly@composewell.com

8-- Stability : experimental

9-- Portability : GHC

10--

12module Streamly.Internal.System.IO

13 ( defaultChunkSize

14 , arrayPayloadSize

15 , unsafeInlineIO

16 )

18where

20-------------------------------------------------------------------------------

21-- Imports

22-------------------------------------------------------------------------------

24import Foreign.Storable (Storable(sizeOf))

25import GHC.Base (realWorld#)

26import GHC.IO (IO(IO))

28-------------------------------------------------------------------------------

29-- API

30-------------------------------------------------------------------------------

32{-# INLINE unsafeInlineIO #-}

33unsafeInlineIO :: IO a -> a

34unsafeInlineIO (IO m) = case m realWorld# of (# _, r #) -> r

36-- | Returns the heap allocation overhead for allocating a byte array. Each

37-- heap object contains a one word header. Byte arrays contain the size of the

38-- array after the header.

39--

40-- See https://gitlab.haskell.org/ghc/ghc/-/wikis/commentary/rts/storage/heap-objects#arrays

41--

42byteArrayOverhead :: Int

43byteArrayOverhead = 2 * sizeOf (undefined :: Word)

45-- | When we allocate a byte array of size @k@ the allocator actually allocates

46-- memory of size @k + byteArrayOverhead@. @arrayPayloadSize n@ returns the

47-- size of the array in bytes that would result in an allocation of @n@ bytes.

48--

49arrayPayloadSize :: Int -> Int

50arrayPayloadSize n = let size = n - byteArrayOverhead in max size 0

52-- | Default maximum buffer size in bytes, for reading from and writing to IO

53-- devices, the value is 32KB minus GHC allocation overhead, which is a few

54-- bytes, so that the actual allocation is 32KB.

55defaultChunkSize :: Int

56defaultChunkSize = arrayPayloadSize (32 * 1024)