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{-# LANGUAGE Safe #-}
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+{-# LANGUAGE CPP #-}
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+{-# LANGUAGE RankNTypes #-}
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-- |
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--
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@@ -14,7 +16,8 @@ |
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--
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module GHC.IO.Handle
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- (Handle,
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+ (-- * Portable operations
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+ Handle,
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BufferMode(..),
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mkFileHandle,
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mkDuplexHandle,
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@@ -70,7 +73,239 @@ module GHC.IO.Handle |
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hGetBuf,
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hGetBufNonBlocking,
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hPutBuf,
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- hPutBufNonBlocking
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- ) where
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+ hPutBufNonBlocking,
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+
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+ -- * Obtaining file descriptors and Windows handles
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+ withReadingFileDescriptor,
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+ withWritingFileDescriptor,
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+ withReadingWindowsHandle,
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+ withWritingWindowsHandle
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+
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+ -- ** Caveats
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+ -- $with-ref-caveats
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+) where
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import GHC.Internal.IO.Handle
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+
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+import GHC.Internal.Control.Monad (return)
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+import GHC.Internal.Control.Exception (mask)
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+import GHC.Internal.Data.Function (const, (.), ($))
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+import GHC.Internal.Data.Functor (fmap)
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+import GHC.Internal.Data.Maybe (Maybe (Nothing), maybe)
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+#if defined(mingw32_HOST_OS)
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+import GHC.Internal.Data.Maybe (Maybe (Just))
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+#endif
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+import GHC.Internal.Data.List ((++))
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+import GHC.Internal.Data.String (String)
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+import GHC.Internal.Data.Typeable (Typeable, cast)
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+import GHC.Internal.System.IO (IO)
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+import GHC.Internal.IO.FD (fdFD)
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+#if defined(mingw32_HOST_OS)
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+import GHC.Internal.IO.Windows.Handle
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+ (
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+ NativeHandle,
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+ ConsoleHandle,
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+ IoHandle,
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+ toHANDLE
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+ )
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+#endif
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+import GHC.Internal.IO.Handle.Types (Handle__)
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+import GHC.Internal.IO.Handle.Internals
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+ (
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+ wantReadableHandle_,
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+ wantWritableHandle,
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+ flushBuffer
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+ )
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+import GHC.Internal.IO.Exception
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+ (
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+ IOErrorType (IllegalOperation),
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+ IOException (IOError),
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+ ioException
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+ )
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+import GHC.Internal.Foreign.Ptr (Ptr)
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+import GHC.Internal.Foreign.C.Types (CInt)
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+
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+-- * Obtaining file descriptors and Windows handles
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+
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+{-|
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+ Obtains from a handle an underlying operating-system reference for reading
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+ or writing and executes a user-provided action on it. The Haskell-side
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+ buffers of the handle are flushed before this action is run. While this
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+ action is executed, further operations on the handle are blocked to a degree
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+ that interference with this action is prevented.
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+
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+ See [below](#with-ref-caveats) for caveats regarding this operation.
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+-}
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+withRef :: (Handle -> (Handle__ -> IO a) -> IO a)
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+ -- ^ Obtaining of an appropriately prepared handle side from a handle
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+ -> (forall d. Typeable d => d -> IO r)
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+ -- ^ Conversion of a device into an operating-system reference
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+ -> Handle
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+ -- ^ The handle to use
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+ -> (r -> IO a)
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+ -- ^ The action to execute on the operating-system reference
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+ -> IO a
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+withRef withHandleSide getRef handle act
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+ = mask $ \ withOriginalMaskingState ->
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+ withHandleSide handle $ \ handleSide -> do
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+ ref <- getRef handleSide
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+ flushBuffer handleSide
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+ withOriginalMaskingState $ act ref
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+{-
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+ The public operations that use 'withRef' provide 'withHandleSide' arguments
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+ that perform masking. Still, we have to use 'mask' here, in order do obtain
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+ the operation that restores the original masking state. The user-provided
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+ action should be executed with this original masking state, as there is no
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+ inherent reason to generally perform it with masking in place. The masking
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+ that the 'withHandleSide' arguments perform is only for safely accessing
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+ internal handle data and thus constitutes an implementation detail; it has
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+ nothing to do with the user-provided action.
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+-}
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+{-
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+ The order of actions in 'withRef' is such that any exception from 'getRef'
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+ is thrown before the flushing of the Haskell-side buffers.
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+-}
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+
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+{-|
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+ Yields the result of another operation if that operation succeeded, and
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+ otherwise throws an exception that signals that the other operation failed
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+ because a certain I/O subsystem is not in use.
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+-}
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+requiringSubsystem :: String
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+ -- ^ The name of the required subsystem
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+ -> Maybe a
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+ -- ^ The result of the other operation if it succeeded
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+ -> IO a
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+requiringSubsystem subsystemName
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+ = maybe (ioException subsystemRequired) return
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+ where
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+
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+ subsystemRequired :: IOException
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+ subsystemRequired = IOError Nothing
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+ IllegalOperation
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+ ""
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+ (subsystemName ++ " I/O subsystem required")
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+ Nothing
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+ Nothing
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+
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+{-|
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+ Obtains the POSIX file descriptor of a device if the POSIX I/O subsystem is
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+ in use, and throws an exception otherwise.
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+-}
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+getFileDescriptor :: Typeable d => d -> IO CInt
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+getFileDescriptor = requiringSubsystem "POSIX" . fmap fdFD . cast
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+
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+{-|
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+ Obtains the Windows handle of a device if the Windows I/O subsystem is in
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+ use, and throws an exception otherwise.
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+-}
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+getWindowsHandle :: Typeable d => d -> IO (Ptr ())
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+getWindowsHandle = requiringSubsystem "native" . toMaybeWindowsHandle where
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+
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+ toMaybeWindowsHandle :: Typeable d => d -> Maybe (Ptr ())
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+#if defined(mingw32_HOST_OS)
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+ toMaybeWindowsHandle dev
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+ | Just nativeHandle <- cast dev :: Maybe (IoHandle NativeHandle)
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+ = Just (toHANDLE nativeHandle)
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+ | Just consoleHandle <- cast dev :: Maybe (IoHandle ConsoleHandle)
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+ = Just (toHANDLE consoleHandle)
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+ | otherwise
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+ = Nothing
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+ {-
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+ This is inspired by the implementation of
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+ 'System.Win32.Types.withHandleToHANDLENative'.
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+ -}
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+#else
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+ toMaybeWindowsHandle = const Nothing
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+#endif
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+
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+{-|
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+ Obtains from a handle a POSIX file descriptor for reading and executes a
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+ user-provided action on it. The Haskell-side buffers of the handle are
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+ flushed before this action is run. While this action is executed, further
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+ operations on the handle are blocked to a degree that interference with this
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+ action is prevented.
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+
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+ If the I/O subsystem in use is not the POSIX one, an exception is thrown.
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+
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+ See [below](#with-ref-caveats) for caveats regarding this operation.
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+-}
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+withReadingFileDescriptor :: Handle -> (CInt -> IO a) -> IO a
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+withReadingFileDescriptor
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+ = withRef (wantReadableHandle_ "withReadingFileDescriptor")
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+ getFileDescriptor
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+
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+{-|
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+ Obtains from a handle a POSIX file descriptor for writing and executes a
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+ user-provided action on it. The Haskell-side buffers of the handle are
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+ flushed before this action is run. While this action is executed, further
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+ operations on the handle are blocked to a degree that interference with this
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+ action is prevented.
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+
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+ If the I/O subsystem in use is not the POSIX one, an exception is thrown.
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+
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+ See [below](#with-ref-caveats) for caveats regarding this operation.
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+-}
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+withWritingFileDescriptor :: Handle -> (CInt -> IO a) -> IO a
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+withWritingFileDescriptor
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+ = withRef (wantWritableHandle "withWritingFileDescriptor")
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+ getFileDescriptor
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+
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+{-|
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+ Obtains from a Haskell handle a Windows handle for reading and executes a
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+ user-provided action on it. The Haskell-side buffers of the Haskell handle
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+ are flushed before this action is run. While this action is executed,
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+ further operations on the handle are blocked to a degree that interference
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+ with this action is prevented.
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+
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+ If the I/O subsystem in use is not the Windows one, an exception is thrown.
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+
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+ See [below](#with-ref-caveats) for caveats regarding this operation.
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+-}
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+withReadingWindowsHandle :: Handle -> (Ptr () -> IO a) -> IO a
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+withReadingWindowsHandle
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+ = withRef (wantReadableHandle_ "withReadingWindowsHandle")
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+ getWindowsHandle
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+
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+{-|
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+ Obtains from a Haskell handle a Windows handle for writing and executes a
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+ user-provided action on it. The Haskell-side buffers of the Haskell handle
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+ are flushed before this action is run. While this action is executed,
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+ further operations on the handle are blocked to a degree that interference
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+ with this action is prevented.
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+
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+ If the I/O subsystem in use is not the Windows one, an exception is thrown.
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+
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+ See [below](#with-ref-caveats) for caveats regarding this operation.
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+-}
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+withWritingWindowsHandle :: Handle -> (Ptr () -> IO a) -> IO a
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+withWritingWindowsHandle
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+ = withRef (wantWritableHandle "withWritingWindowsHandle")
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+ getWindowsHandle
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+
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286
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+-- ** Caveats
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287
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+
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288
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+{-$with-ref-caveats
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289
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+ #with-ref-caveats#There are the following caveats regarding each of the
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290
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+ above operations:
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+
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+ * The flushing of buffers can fail if the given handle is readable but not
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+ seekable.
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+
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+ * If the operation is performed as part of an action executed by
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+ 'unsafePerformIO', 'unsafeInterleaveIO', or one of their “dupable”
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297
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+ variants and the user-provided action receives an asychnchronous
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298
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+ exception and does not catch it, then the following happens:
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+
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+ - Before the overall computation is suspended, the blocking of handle
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+ operations is removed.
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+
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303
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+ - When the computation is later resumed due to another evaluation
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+ attempt, the blocking of handle operations is reinstantiated, the
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+ Haskell-side buffers are flushed again, and the user-provided action
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+ is run from the beginning.
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307
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+
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308
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+ Repeating the previously executed part of the user-provided action
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309
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+ cannot be avoided apparently. See the @[async]@ note in the source code
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310
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+ of "GHC.Internal.IO.Handle.Internals" for further explanation.
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311
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+-} |