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|
{-# LANGUAGE Unsafe #-}
{-# LANGUAGE NoImplicitPrelude #-}
-----------------------------------------------------------------------------
-- |
-- Module : System.IO.Unsafe
-- Copyright : (c) The University of Glasgow 2001
-- License : BSD-style (see the file libraries/base/LICENSE)
--
-- Maintainer : libraries@haskell.org
-- Stability : provisional
-- Portability : portable
--
-- \"Unsafe\" IO operations.
--
-----------------------------------------------------------------------------
module System.IO.Unsafe (
-- * Unsafe 'System.IO.IO' operations
unsafePerformIO,
unsafeDupablePerformIO,
unsafeInterleaveIO,
unsafeFixIO,
) where
import GHC.Base
import GHC.IO
import GHC.IORef
import GHC.Exception
import Control.Exception
-- | A slightly faster version of `System.IO.fixIO` that may not be
-- safe to use with multiple threads. The unsafety arises when used
-- like this:
--
-- > unsafeFixIO $ \r -> do
-- > forkIO (print r)
-- > return (...)
--
-- In this case, the child thread will receive a @NonTermination@
-- exception instead of waiting for the value of @r@ to be computed.
--
-- @since 4.5.0.0
unsafeFixIO :: (a -> IO a) -> IO a
unsafeFixIO k = do
ref <- newIORef (throw NonTermination)
ans <- unsafeDupableInterleaveIO (readIORef ref)
result <- k ans
writeIORef ref result
return result
|
