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{-# LANGUAGE ForeignFunctionInterface #-}
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{-# OPTIONS_GHC -fno-warn-unused-imports #-}

-----------------------------------------------------------------------------
-- |
-- Module      :  System.Posix.SharedMem
-- Copyright   :  (c) Daniel Franke 2007
-- License     :  BSD-style (see the file libraries/base/LICENSE)
--
-- Maintainer  :  [email protected]
-- Stability   :  experimental
-- Portability :  non-portable (requires POSIX)
--
-- POSIX shared memory support.
--
-----------------------------------------------------------------------------

module System.Posix.SharedMem
    (ShmOpenFlags(..), shmOpen, shmUnlink)
    where


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import System.Posix.Types
import System.Posix.Error
import Foreign.C
import Data.Bits

data ShmOpenFlags = ShmOpenFlags 
    { shmReadWrite :: Bool,
      -- ^ If true, open the shm object read-write rather than read-only. 
      shmCreate :: Bool,
      -- ^ If true, create the shm object if it does not exist. 
      shmExclusive :: Bool,
      -- ^ If true, throw an exception if the shm object already exists.
      shmTrunc :: Bool
      -- ^ If true, wipe the contents of the shm object after opening it.
    }

-- | Open a shared memory object with the given name, flags, and mode.
shmOpen :: String -> ShmOpenFlags -> FileMode -> IO Fd

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shmOpen name flags mode =
    do cflags0 <- return 0
       cflags1 <- return $ cflags0 .|. (if shmReadWrite flags
                                        then 2
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                                        else 0)
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       cflags2 <- return $ cflags1 .|. (if shmCreate flags then 64 
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                                        else 0)
       cflags3 <- return $ cflags2 .|. (if shmExclusive flags 
                                        then 128 
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                                        else 0)
       cflags4 <- return $ cflags3 .|. (if shmTrunc flags then 512 
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                                        else 0)
       withCAString name (shmOpen' cflags4)
    where shmOpen' cflags cname =
              do fd <- throwErrnoIfMinus1 "shmOpen" $ 
                       shm_open cname cflags mode
                 return $ Fd fd

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-- | Delete the shared memory object with the given name.
shmUnlink :: String -> IO ()

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shmUnlink name = withCAString name shmUnlink'
    where shmUnlink' cname =
              throwErrnoIfMinus1_ "shmUnlink" $ shm_unlink cname

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foreign import ccall unsafe "shm_open"
        shm_open :: CString -> CInt -> CMode -> IO CInt

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foreign import ccall unsafe "shm_unlink"
        shm_unlink :: CString -> IO CInt

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