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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 :: forall a. (a -> IO a) -> IO a unsafeFixIO a -> IO a k = do IORef a ref <- a -> IO (IORef a) forall a. a -> IO (IORef a) newIORef (NonTermination -> a forall a e. Exception e => e -> a throw NonTermination NonTermination) a ans <- IO a -> IO a forall a. IO a -> IO a unsafeDupableInterleaveIO (IORef a -> IO a forall a. IORef a -> IO a readIORef IORef a ref) a result <- a -> IO a k a ans IORef a -> a -> IO () forall a. IORef a -> a -> IO () writeIORef IORef a ref a result a -> IO a forall a. a -> IO a forall (m :: * -> *) a. Monad m => a -> m a return a result