-{-# OPTIONS_GHC -XNoImplicitPrelude -#include "HsBase.h" #-}
+{-# OPTIONS_GHC -fno-implicit-prelude -funbox-strict-fields #-}
{-# OPTIONS_HADDOCK hide #-}
-
-#undef DEBUG_DUMP
-
-----------------------------------------------------------------------------
-- |
-- Module : GHC.IO
--- Copyright : (c) The University of Glasgow, 1992-2001
+-- Copyright : (c) The University of Glasgow 1994-2002
-- License : see libraries/base/LICENSE
--
--- Maintainer : libraries@haskell.org
+-- Maintainer : cvs-ghc@haskell.org
-- Stability : internal
--- Portability : non-portable
+-- Portability : non-portable (GHC Extensions)
--
--- String I\/O functions
+-- Definitions for the 'IO' monad and its friends.
--
-----------------------------------------------------------------------------
-- #hide
-module GHC.IO (
- hWaitForInput, hGetChar, hGetLine, hGetContents, hPutChar, hPutStr,
- commitBuffer', -- hack, see below
- hGetcBuffered, -- needed by ghc/compiler/utils/StringBuffer.lhs
- hGetBuf, hGetBufNonBlocking, hPutBuf, hPutBufNonBlocking, slurpFile,
- memcpy_ba_baoff,
- memcpy_ptr_baoff,
- memcpy_baoff_ba,
- memcpy_baoff_ptr,
- ) where
-
-import Foreign
-import Foreign.C
-
-import System.IO.Error
-import Data.Maybe
-import Control.Monad
-#ifndef mingw32_HOST_OS
-import System.Posix.Internals
-#endif
+module GHC.IO (
+ IO(..), unIO, failIO, liftIO, bindIO, thenIO, returnIO,
+ unsafePerformIO, unsafeInterleaveIO,
+ unsafeDupablePerformIO, unsafeDupableInterleaveIO,
+ noDuplicate,
+
+ -- To and from from ST
+ stToIO, ioToST, unsafeIOToST, unsafeSTToIO,
+
+ FilePath,
+
+ catchException, catchAny, throwIO,
+ block, unblock, blocked,
+ onException, finally, evaluate
+ ) where
-import GHC.Enum
import GHC.Base
-import GHC.IOBase
-import GHC.Handle -- much of the real stuff is in here
-import GHC.Real
-import GHC.Num
-import GHC.Show
-import GHC.List
+import GHC.ST
+import GHC.Exception
+import Data.Maybe
-#ifdef mingw32_HOST_OS
-import GHC.Conc
-#endif
+import {-# SOURCE #-} GHC.IO.Exception ( userError )
-- ---------------------------------------------------------------------------
--- Simple input operations
+-- The IO Monad
--- If hWaitForInput finds anything in the Handle's buffer, it
--- immediately returns. If not, it tries to read from the underlying
--- OS handle. Notice that for buffered Handles connected to terminals
--- this means waiting until a complete line is available.
+{-
+The IO Monad is just an instance of the ST monad, where the state is
+the real world. We use the exception mechanism (in GHC.Exception) to
+implement IO exceptions.
--- | Computation 'hWaitForInput' @hdl t@
--- waits until input is available on handle @hdl@.
--- It returns 'True' as soon as input is available on @hdl@,
--- or 'False' if no input is available within @t@ milliseconds.
---
--- If @t@ is less than zero, then @hWaitForInput@ waits indefinitely.
---
--- This operation may fail with:
---
--- * 'isEOFError' if the end of file has been reached.
---
--- NOTE for GHC users: unless you use the @-threaded@ flag,
--- @hWaitForInput t@ where @t >= 0@ will block all other Haskell
--- threads for the duration of the call. It behaves like a
--- @safe@ foreign call in this respect.
-
-hWaitForInput :: Handle -> Int -> IO Bool
-hWaitForInput h msecs = do
- wantReadableHandle "hWaitForInput" h $ \ handle_ -> do
- let ref = haBuffer handle_
- buf <- readIORef ref
-
- if not (bufferEmpty buf)
- then return True
- else do
-
- if msecs < 0
- then do buf' <- fillReadBuffer (haFD handle_) True
- (haIsStream handle_) buf
- writeIORef ref buf'
- return True
- else do r <- throwErrnoIfMinus1Retry "hWaitForInput" $
- fdReady (haFD handle_) 0 {- read -}
- (fromIntegral msecs)
- (fromIntegral $ fromEnum $ haIsStream handle_)
- if r /= 0 then do -- Call hLookAhead' to throw an EOF
- -- exception if appropriate
- hLookAhead' handle_
- return True
- else return False
-
-foreign import ccall safe "fdReady"
- fdReady :: CInt -> CInt -> CInt -> CInt -> IO CInt
+NOTE: The IO representation is deeply wired in to various parts of the
+system. The following list may or may not be exhaustive:
--- ---------------------------------------------------------------------------
--- hGetChar
+Compiler - types of various primitives in PrimOp.lhs
--- | Computation 'hGetChar' @hdl@ reads a character from the file or
--- channel managed by @hdl@, blocking until a character is available.
---
--- This operation may fail with:
---
--- * 'isEOFError' if the end of file has been reached.
-
-hGetChar :: Handle -> IO Char
-hGetChar handle =
- wantReadableHandle "hGetChar" handle $ \handle_ -> do
-
- let fd = haFD handle_
- ref = haBuffer handle_
-
- buf <- readIORef ref
- if not (bufferEmpty buf)
- then hGetcBuffered fd ref buf
- else do
-
- -- buffer is empty.
- case haBufferMode handle_ of
- LineBuffering -> do
- new_buf <- fillReadBuffer fd True (haIsStream handle_) buf
- hGetcBuffered fd ref new_buf
- BlockBuffering _ -> do
- new_buf <- fillReadBuffer fd True (haIsStream handle_) buf
- -- ^^^^
- -- don't wait for a completely full buffer.
- hGetcBuffered fd ref new_buf
- NoBuffering -> do
- -- make use of the minimal buffer we already have
- let !raw = bufBuf buf
- r <- readRawBuffer "hGetChar" fd (haIsStream handle_) raw 0 1
- if r == 0
- then ioe_EOF
- else do (c,_) <- readCharFromBuffer raw 0
- return c
-
-hGetcBuffered :: FD -> IORef Buffer -> Buffer -> IO Char
-hGetcBuffered _ ref buf@Buffer{ bufBuf=b, bufRPtr=r0, bufWPtr=w }
- = do (c, r) <- readCharFromBuffer b r0
- let new_buf | r == w = buf{ bufRPtr=0, bufWPtr=0 }
- | otherwise = buf{ bufRPtr=r }
- writeIORef ref new_buf
- return c
+RTS - forceIO (StgMiscClosures.hc)
+ - catchzh_fast, (un)?blockAsyncExceptionszh_fast, raisezh_fast
+ (Exceptions.hc)
+ - raiseAsync (Schedule.c)
--- ---------------------------------------------------------------------------
--- hGetLine
+Prelude - GHC.IO.lhs, and several other places including
+ GHC.Exception.lhs.
--- ToDo: the unbuffered case is wrong: it doesn't lock the handle for
--- the duration.
+Libraries - parts of hslibs/lang.
--- | Computation 'hGetLine' @hdl@ reads a line from the file or
--- channel managed by @hdl@.
---
--- This operation may fail with:
---
--- * 'isEOFError' if the end of file is encountered when reading
--- the /first/ character of the line.
---
--- If 'hGetLine' encounters end-of-file at any other point while reading
--- in a line, it is treated as a line terminator and the (partial)
--- line is returned.
-
-hGetLine :: Handle -> IO String
-hGetLine h = do
- m <- wantReadableHandle "hGetLine" h $ \ handle_ -> do
- case haBufferMode handle_ of
- NoBuffering -> return Nothing
- LineBuffering -> do
- l <- hGetLineBuffered handle_
- return (Just l)
- BlockBuffering _ -> do
- l <- hGetLineBuffered handle_
- return (Just l)
- case m of
- Nothing -> hGetLineUnBuffered h
- Just l -> return l
-
-hGetLineBuffered :: Handle__ -> IO String
-hGetLineBuffered handle_ = do
- let ref = haBuffer handle_
- buf <- readIORef ref
- hGetLineBufferedLoop handle_ ref buf []
-
-hGetLineBufferedLoop :: Handle__ -> IORef Buffer -> Buffer -> [String]
- -> IO String
-hGetLineBufferedLoop handle_ ref
- buf@Buffer{ bufRPtr=r0, bufWPtr=w, bufBuf=raw0 } xss =
- let
- -- find the end-of-line character, if there is one
- loop raw r
- | r == w = return (False, w)
- | otherwise = do
- (c,r') <- readCharFromBuffer raw r
- if c == '\n'
- then return (True, r) -- NB. not r': don't include the '\n'
- else loop raw r'
- in do
- (eol, off) <- loop raw0 r0
-
-#ifdef DEBUG_DUMP
- puts ("hGetLineBufferedLoop: r=" ++ show r0 ++ ", w=" ++ show w ++ ", off=" ++ show off ++ "\n")
-#endif
-
- xs <- unpack raw0 r0 off
-
- -- if eol == True, then off is the offset of the '\n'
- -- otherwise off == w and the buffer is now empty.
- if eol
- then do if (w == off + 1)
- then writeIORef ref buf{ bufRPtr=0, bufWPtr=0 }
- else writeIORef ref buf{ bufRPtr = off + 1 }
- return (concat (reverse (xs:xss)))
- else do
- maybe_buf <- maybeFillReadBuffer (haFD handle_) True (haIsStream handle_)
- buf{ bufWPtr=0, bufRPtr=0 }
- case maybe_buf of
- -- Nothing indicates we caught an EOF, and we may have a
- -- partial line to return.
- Nothing -> do
- writeIORef ref buf{ bufRPtr=0, bufWPtr=0 }
- let str = concat (reverse (xs:xss))
- if not (null str)
- then return str
- else ioe_EOF
- Just new_buf ->
- hGetLineBufferedLoop handle_ ref new_buf (xs:xss)
-
-maybeFillReadBuffer :: FD -> Bool -> Bool -> Buffer -> IO (Maybe Buffer)
-maybeFillReadBuffer fd is_line is_stream buf
- = catch
- (do buf' <- fillReadBuffer fd is_line is_stream buf
- return (Just buf')
- )
- (\e -> do if isEOFError e
- then return Nothing
- else ioError e)
-
-
-unpack :: RawBuffer -> Int -> Int -> IO [Char]
-unpack _ _ 0 = return ""
-unpack buf (I# r) (I# len) = IO $ \s -> unpackRB [] (len -# 1#) s
- where
- unpackRB acc i s
- | i <# r = (# s, acc #)
- | otherwise =
- case readCharArray# buf i s of
- (# s', ch #) -> unpackRB (C# ch : acc) (i -# 1#) s'
-
-
-hGetLineUnBuffered :: Handle -> IO String
-hGetLineUnBuffered h = do
- c <- hGetChar h
- if c == '\n' then
- return ""
- else do
- l <- getRest
- return (c:l)
- where
- getRest = do
- c <-
- catch
- (hGetChar h)
- (\ err -> do
- if isEOFError err then
- return '\n'
- else
- ioError err)
- if c == '\n' then
- return ""
- else do
- s <- getRest
- return (c:s)
+--SDM
+-}
--- -----------------------------------------------------------------------------
--- hGetContents
+{-|
+A value of type @'IO' a@ is a computation which, when performed,
+does some I\/O before returning a value of type @a@.
--- hGetContents on a DuplexHandle only affects the read side: you can
--- carry on writing to it afterwards.
+There is really only one way to \"perform\" an I\/O action: bind it to
+@Main.main@ in your program. When your program is run, the I\/O will
+be performed. It isn't possible to perform I\/O from an arbitrary
+function, unless that function is itself in the 'IO' monad and called
+at some point, directly or indirectly, from @Main.main@.
--- | Computation 'hGetContents' @hdl@ returns the list of characters
--- corresponding to the unread portion of the channel or file managed
--- by @hdl@, which is put into an intermediate state, /semi-closed/.
--- In this state, @hdl@ is effectively closed,
--- but items are read from @hdl@ on demand and accumulated in a special
--- list returned by 'hGetContents' @hdl@.
---
--- Any operation that fails because a handle is closed,
--- also fails if a handle is semi-closed. The only exception is 'hClose'.
--- A semi-closed handle becomes closed:
---
--- * if 'hClose' is applied to it;
---
--- * if an I\/O error occurs when reading an item from the handle;
---
--- * or once the entire contents of the handle has been read.
---
--- Once a semi-closed handle becomes closed, the contents of the
--- associated list becomes fixed. The contents of this final list is
--- only partially specified: it will contain at least all the items of
--- the stream that were evaluated prior to the handle becoming closed.
---
--- Any I\/O errors encountered while a handle is semi-closed are simply
--- discarded.
---
--- This operation may fail with:
---
--- * 'isEOFError' if the end of file has been reached.
-
-hGetContents :: Handle -> IO String
-hGetContents handle =
- withHandle "hGetContents" handle $ \handle_ ->
- case haType handle_ of
- ClosedHandle -> ioe_closedHandle
- SemiClosedHandle -> ioe_closedHandle
- AppendHandle -> ioe_notReadable
- WriteHandle -> ioe_notReadable
- _ -> do xs <- lazyRead handle
- return (handle_{ haType=SemiClosedHandle}, xs )
-
--- Note that someone may close the semi-closed handle (or change its
--- buffering), so each time these lazy read functions are pulled on,
--- they have to check whether the handle has indeed been closed.
-
-lazyRead :: Handle -> IO String
-lazyRead handle =
- unsafeInterleaveIO $
- withHandle "lazyRead" handle $ \ handle_ -> do
- case haType handle_ of
- ClosedHandle -> return (handle_, "")
- SemiClosedHandle -> lazyRead' handle handle_
- _ -> ioException
- (IOError (Just handle) IllegalOperation "lazyRead"
- "illegal handle type" Nothing Nothing)
-
-lazyRead' :: Handle -> Handle__ -> IO (Handle__, [Char])
-lazyRead' h handle_ = do
- let ref = haBuffer handle_
- fd = haFD handle_
-
- -- even a NoBuffering handle can have a char in the buffer...
- -- (see hLookAhead)
- buf <- readIORef ref
- if not (bufferEmpty buf)
- then lazyReadHaveBuffer h handle_ fd ref buf
- else do
-
- case haBufferMode handle_ of
- NoBuffering -> do
- -- make use of the minimal buffer we already have
- let !raw = bufBuf buf
- r <- readRawBuffer "lazyRead" fd (haIsStream handle_) raw 0 1
- if r == 0
- then do (handle_', _) <- hClose_help handle_
- return (handle_', "")
- else do (c,_) <- readCharFromBuffer raw 0
- rest <- lazyRead h
- return (handle_, c : rest)
-
- LineBuffering -> lazyReadBuffered h handle_ fd ref buf
- BlockBuffering _ -> lazyReadBuffered h handle_ fd ref buf
-
--- we never want to block during the read, so we call fillReadBuffer with
--- is_line==True, which tells it to "just read what there is".
-lazyReadBuffered :: Handle -> Handle__ -> FD -> IORef Buffer -> Buffer
- -> IO (Handle__, [Char])
-lazyReadBuffered h handle_ fd ref buf = do
- catch
- (do buf' <- fillReadBuffer fd True{-is_line-} (haIsStream handle_) buf
- lazyReadHaveBuffer h handle_ fd ref buf'
- )
- -- all I/O errors are discarded. Additionally, we close the handle.
- (\_ -> do (handle_', _) <- hClose_help handle_
- return (handle_', "")
- )
-
-lazyReadHaveBuffer :: Handle -> Handle__ -> FD -> IORef Buffer -> Buffer -> IO (Handle__, [Char])
-lazyReadHaveBuffer h handle_ _ ref buf = do
- more <- lazyRead h
- writeIORef ref buf{ bufRPtr=0, bufWPtr=0 }
- s <- unpackAcc (bufBuf buf) (bufRPtr buf) (bufWPtr buf) more
- return (handle_, s)
-
-
-unpackAcc :: RawBuffer -> Int -> Int -> [Char] -> IO [Char]
-unpackAcc _ _ 0 acc = return acc
-unpackAcc buf (I# r) (I# len) acc0 = IO $ \s -> unpackRB acc0 (len -# 1#) s
- where
- unpackRB acc i s
- | i <# r = (# s, acc #)
- | otherwise =
- case readCharArray# buf i s of
- (# s', ch #) -> unpackRB (C# ch : acc) (i -# 1#) s'
+'IO' is a monad, so 'IO' actions can be combined using either the do-notation
+or the '>>' and '>>=' operations from the 'Monad' class.
+-}
+newtype IO a = IO (State# RealWorld -> (# State# RealWorld, a #))
+
+unIO :: IO a -> (State# RealWorld -> (# State# RealWorld, a #))
+unIO (IO a) = a
+
+instance Functor IO where
+ fmap f x = x >>= (return . f)
+
+instance Monad IO where
+ {-# INLINE return #-}
+ {-# INLINE (>>) #-}
+ {-# INLINE (>>=) #-}
+ m >> k = m >>= \ _ -> k
+ return x = returnIO x
+
+ m >>= k = bindIO m k
+ fail s = failIO s
+
+liftIO :: IO a -> State# RealWorld -> STret RealWorld a
+liftIO (IO m) = \s -> case m s of (# s', r #) -> STret s' r
+
+bindIO :: IO a -> (a -> IO b) -> IO b
+bindIO (IO m) k = IO ( \ s ->
+ case m s of
+ (# new_s, a #) -> unIO (k a) new_s
+ )
+
+thenIO :: IO a -> IO b -> IO b
+thenIO (IO m) k = IO ( \ s ->
+ case m s of
+ (# new_s, _ #) -> unIO k new_s
+ )
+
+returnIO :: a -> IO a
+returnIO x = IO (\ s -> (# s, x #))
+
+failIO :: String -> IO a
+failIO s = IO (raiseIO# (toException (userError s)))
-- ---------------------------------------------------------------------------
--- hPutChar
+-- Coercions between IO and ST
--- | Computation 'hPutChar' @hdl ch@ writes the character @ch@ to the
--- file or channel managed by @hdl@. Characters may be buffered if
--- buffering is enabled for @hdl@.
---
--- This operation may fail with:
---
--- * 'isFullError' if the device is full; or
+-- | A monad transformer embedding strict state transformers in the 'IO'
+-- monad. The 'RealWorld' parameter indicates that the internal state
+-- used by the 'ST' computation is a special one supplied by the 'IO'
+-- monad, and thus distinct from those used by invocations of 'runST'.
+stToIO :: ST RealWorld a -> IO a
+stToIO (ST m) = IO m
+
+ioToST :: IO a -> ST RealWorld a
+ioToST (IO m) = (ST m)
+
+-- This relies on IO and ST having the same representation modulo the
+-- constraint on the type of the state
--
--- * 'isPermissionError' if another system resource limit would be exceeded.
-
-hPutChar :: Handle -> Char -> IO ()
-hPutChar handle c = do
- c `seq` return ()
- wantWritableHandle "hPutChar" handle $ \ handle_ -> do
- let fd = haFD handle_
- case haBufferMode handle_ of
- LineBuffering -> hPutcBuffered handle_ True c
- BlockBuffering _ -> hPutcBuffered handle_ False c
- NoBuffering ->
- with (castCharToCChar c) $ \buf -> do
- writeRawBufferPtr "hPutChar" fd (haIsStream handle_) buf 0 1
- return ()
-
-hPutcBuffered :: Handle__ -> Bool -> Char -> IO ()
-hPutcBuffered handle_ is_line c = do
- let ref = haBuffer handle_
- buf <- readIORef ref
- let w = bufWPtr buf
- w' <- writeCharIntoBuffer (bufBuf buf) w c
- let new_buf = buf{ bufWPtr = w' }
- if bufferFull new_buf || is_line && c == '\n'
- then do
- flushed_buf <- flushWriteBuffer (haFD handle_) (haIsStream handle_) new_buf
- writeIORef ref flushed_buf
- else do
- writeIORef ref new_buf
-
-
-hPutChars :: Handle -> [Char] -> IO ()
-hPutChars _ [] = return ()
-hPutChars handle (c:cs) = hPutChar handle c >> hPutChars handle cs
+unsafeIOToST :: IO a -> ST s a
+unsafeIOToST (IO io) = ST $ \ s -> (unsafeCoerce# io) s
+
+unsafeSTToIO :: ST s a -> IO a
+unsafeSTToIO (ST m) = IO (unsafeCoerce# m)
-- ---------------------------------------------------------------------------
--- hPutStr
+-- Unsafe IO operations
+
+{-|
+This is the \"back door\" into the 'IO' monad, allowing
+'IO' computation to be performed at any time. For
+this to be safe, the 'IO' computation should be
+free of side effects and independent of its environment.
+
+If the I\/O computation wrapped in 'unsafePerformIO'
+performs side effects, then the relative order in which those side
+effects take place (relative to the main I\/O trunk, or other calls to
+'unsafePerformIO') is indeterminate. You have to be careful when
+writing and compiling modules that use 'unsafePerformIO':
+
+ * Use @{\-\# NOINLINE foo \#-\}@ as a pragma on any function @foo@
+ that calls 'unsafePerformIO'. If the call is inlined,
+ the I\/O may be performed more than once.
+
+ * Use the compiler flag @-fno-cse@ to prevent common sub-expression
+ elimination being performed on the module, which might combine
+ two side effects that were meant to be separate. A good example
+ is using multiple global variables (like @test@ in the example below).
+
+ * Make sure that the either you switch off let-floating, or that the
+ call to 'unsafePerformIO' cannot float outside a lambda. For example,
+ if you say:
+ @
+ f x = unsafePerformIO (newIORef [])
+ @
+ you may get only one reference cell shared between all calls to @f@.
+ Better would be
+ @
+ f x = unsafePerformIO (newIORef [x])
+ @
+ because now it can't float outside the lambda.
+
+It is less well known that
+'unsafePerformIO' is not type safe. For example:
+
+> test :: IORef [a]
+> test = unsafePerformIO $ newIORef []
+>
+> main = do
+> writeIORef test [42]
+> bang <- readIORef test
+> print (bang :: [Char])
+
+This program will core dump. This problem with polymorphic references
+is well known in the ML community, and does not arise with normal
+monadic use of references. There is no easy way to make it impossible
+once you use 'unsafePerformIO'. Indeed, it is
+possible to write @coerce :: a -> b@ with the
+help of 'unsafePerformIO'. So be careful!
+-}
+unsafePerformIO :: IO a -> a
+unsafePerformIO m = unsafeDupablePerformIO (noDuplicate >> m)
+
+{-|
+This version of 'unsafePerformIO' is slightly more efficient,
+because it omits the check that the IO is only being performed by a
+single thread. Hence, when you write 'unsafeDupablePerformIO',
+there is a possibility that the IO action may be performed multiple
+times (on a multiprocessor), and you should therefore ensure that
+it gives the same results each time.
+-}
+{-# NOINLINE unsafeDupablePerformIO #-}
+unsafeDupablePerformIO :: IO a -> a
+unsafeDupablePerformIO (IO m) = lazy (case m realWorld# of (# _, r #) -> r)
+
+-- Why do we NOINLINE unsafeDupablePerformIO? See the comment with
+-- GHC.ST.runST. Essentially the issue is that the IO computation
+-- inside unsafePerformIO must be atomic: it must either all run, or
+-- not at all. If we let the compiler see the application of the IO
+-- to realWorld#, it might float out part of the IO.
+
+-- Why is there a call to 'lazy' in unsafeDupablePerformIO?
+-- If we don't have it, the demand analyser discovers the following strictness
+-- for unsafeDupablePerformIO: C(U(AV))
+-- But then consider
+-- unsafeDupablePerformIO (\s -> let r = f x in
+-- case writeIORef v r s of (# s1, _ #) ->
+-- (# s1, r #)
+-- The strictness analyser will find that the binding for r is strict,
+-- (becuase of uPIO's strictness sig), and so it'll evaluate it before
+-- doing the writeIORef. This actually makes tests/lib/should_run/memo002
+-- get a deadlock!
+--
+-- Solution: don't expose the strictness of unsafeDupablePerformIO,
+-- by hiding it with 'lazy'
+
+{-|
+'unsafeInterleaveIO' allows 'IO' computation to be deferred lazily.
+When passed a value of type @IO a@, the 'IO' will only be performed
+when the value of the @a@ is demanded. This is used to implement lazy
+file reading, see 'System.IO.hGetContents'.
+-}
+{-# INLINE unsafeInterleaveIO #-}
+unsafeInterleaveIO :: IO a -> IO a
+unsafeInterleaveIO m = unsafeDupableInterleaveIO (noDuplicate >> m)
+
+-- We believe that INLINE on unsafeInterleaveIO is safe, because the
+-- state from this IO thread is passed explicitly to the interleaved
+-- IO, so it cannot be floated out and shared.
+
+{-# INLINE unsafeDupableInterleaveIO #-}
+unsafeDupableInterleaveIO :: IO a -> IO a
+unsafeDupableInterleaveIO (IO m)
+ = IO ( \ s -> let
+ r = case m s of (# _, res #) -> res
+ in
+ (# s, r #))
+
+{-|
+Ensures that the suspensions under evaluation by the current thread
+are unique; that is, the current thread is not evaluating anything
+that is also under evaluation by another thread that has also executed
+'noDuplicate'.
+
+This operation is used in the definition of 'unsafePerformIO' to
+prevent the IO action from being executed multiple times, which is usually
+undesirable.
+-}
+noDuplicate :: IO ()
+noDuplicate = IO $ \s -> case noDuplicate# s of s' -> (# s', () #)
--- We go to some trouble to avoid keeping the handle locked while we're
--- evaluating the string argument to hPutStr, in case doing so triggers another
--- I/O operation on the same handle which would lead to deadlock. The classic
--- case is
---
--- putStr (trace "hello" "world")
---
--- so the basic scheme is this:
---
--- * copy the string into a fresh buffer,
--- * "commit" the buffer to the handle.
---
--- Committing may involve simply copying the contents of the new
--- buffer into the handle's buffer, flushing one or both buffers, or
--- maybe just swapping the buffers over (if the handle's buffer was
--- empty). See commitBuffer below.
+-- -----------------------------------------------------------------------------
+-- | File and directory names are values of type 'String', whose precise
+-- meaning is operating system dependent. Files can be opened, yielding a
+-- handle which can then be used to operate on the contents of that file.
--- | Computation 'hPutStr' @hdl s@ writes the string
--- @s@ to the file or channel managed by @hdl@.
---
--- This operation may fail with:
---
--- * 'isFullError' if the device is full; or
---
--- * 'isPermissionError' if another system resource limit would be exceeded.
-
-hPutStr :: Handle -> String -> IO ()
-hPutStr handle str = do
- buffer_mode <- wantWritableHandle "hPutStr" handle
- (\ handle_ -> do getSpareBuffer handle_)
- case buffer_mode of
- (NoBuffering, _) -> do
- hPutChars handle str -- v. slow, but we don't care
- (LineBuffering, buf) -> do
- writeLines handle buf str
- (BlockBuffering _, buf) -> do
- writeBlocks handle buf str
-
-
-getSpareBuffer :: Handle__ -> IO (BufferMode, Buffer)
-getSpareBuffer Handle__{haBuffer=ref,
- haBuffers=spare_ref,
- haBufferMode=mode}
- = do
- case mode of
- NoBuffering -> return (mode, error "no buffer!")
- _ -> do
- bufs <- readIORef spare_ref
- buf <- readIORef ref
- case bufs of
- BufferListCons b rest -> do
- writeIORef spare_ref rest
- return ( mode, newEmptyBuffer b WriteBuffer (bufSize buf))
- BufferListNil -> do
- new_buf <- allocateBuffer (bufSize buf) WriteBuffer
- return (mode, new_buf)
-
-
-writeLines :: Handle -> Buffer -> String -> IO ()
-writeLines hdl Buffer{ bufBuf=raw, bufSize=len } s =
- let
- shoveString :: Int -> [Char] -> IO ()
- -- check n == len first, to ensure that shoveString is strict in n.
- shoveString n cs | n == len = do
- new_buf <- commitBuffer hdl raw len n True{-needs flush-} False
- writeLines hdl new_buf cs
- shoveString n [] = do
- commitBuffer hdl raw len n False{-no flush-} True{-release-}
- return ()
- shoveString n (c:cs) = do
- n' <- writeCharIntoBuffer raw n c
- if (c == '\n')
- then do
- new_buf <- commitBuffer hdl raw len n' True{-needs flush-} False
- writeLines hdl new_buf cs
- else
- shoveString n' cs
- in
- shoveString 0 s
-
-writeBlocks :: Handle -> Buffer -> String -> IO ()
-writeBlocks hdl Buffer{ bufBuf=raw, bufSize=len } s =
- let
- shoveString :: Int -> [Char] -> IO ()
- -- check n == len first, to ensure that shoveString is strict in n.
- shoveString n cs | n == len = do
- new_buf <- commitBuffer hdl raw len n True{-needs flush-} False
- writeBlocks hdl new_buf cs
- shoveString n [] = do
- commitBuffer hdl raw len n False{-no flush-} True{-release-}
- return ()
- shoveString n (c:cs) = do
- n' <- writeCharIntoBuffer raw n c
- shoveString n' cs
- in
- shoveString 0 s
+type FilePath = String
-- -----------------------------------------------------------------------------
--- commitBuffer handle buf sz count flush release
---
--- Write the contents of the buffer 'buf' ('sz' bytes long, containing
--- 'count' bytes of data) to handle (handle must be block or line buffered).
---
--- Implementation:
---
--- for block/line buffering,
--- 1. If there isn't room in the handle buffer, flush the handle
--- buffer.
---
--- 2. If the handle buffer is empty,
--- if flush,
--- then write buf directly to the device.
--- else swap the handle buffer with buf.
---
--- 3. If the handle buffer is non-empty, copy buf into the
--- handle buffer. Then, if flush != 0, flush
--- the buffer.
-
-commitBuffer
- :: Handle -- handle to commit to
- -> RawBuffer -> Int -- address and size (in bytes) of buffer
- -> Int -- number of bytes of data in buffer
- -> Bool -- True <=> flush the handle afterward
- -> Bool -- release the buffer?
- -> IO Buffer
-
-commitBuffer hdl raw sz@(I# _) count@(I# _) flush release = do
- wantWritableHandle "commitAndReleaseBuffer" hdl $
- commitBuffer' raw sz count flush release
-
--- Explicitly lambda-lift this function to subvert GHC's full laziness
--- optimisations, which otherwise tends to float out subexpressions
--- past the \handle, which is really a pessimisation in this case because
--- that lambda is a one-shot lambda.
---
--- Don't forget to export the function, to stop it being inlined too
--- (this appears to be better than NOINLINE, because the strictness
--- analyser still gets to worker-wrapper it).
---
--- This hack is a fairly big win for hPutStr performance. --SDM 18/9/2001
---
-commitBuffer' :: RawBuffer -> Int -> Int -> Bool -> Bool -> Handle__
- -> IO Buffer
-commitBuffer' raw sz@(I# _) count@(I# _) flush release
- handle_@Handle__{ haFD=fd, haBuffer=ref, haBuffers=spare_buf_ref } = do
-
-#ifdef DEBUG_DUMP
- puts ("commitBuffer: sz=" ++ show sz ++ ", count=" ++ show count
- ++ ", flush=" ++ show flush ++ ", release=" ++ show release ++"\n")
-#endif
-
- old_buf@Buffer{ bufBuf=old_raw, bufWPtr=w, bufSize=size }
- <- readIORef ref
-
- buf_ret <-
- -- enough room in handle buffer?
- if (not flush && (size - w > count))
- -- The > is to be sure that we never exactly fill
- -- up the buffer, which would require a flush. So
- -- if copying the new data into the buffer would
- -- make the buffer full, we just flush the existing
- -- buffer and the new data immediately, rather than
- -- copying before flushing.
-
- -- not flushing, and there's enough room in the buffer:
- -- just copy the data in and update bufWPtr.
- then do memcpy_baoff_ba old_raw (fromIntegral w) raw (fromIntegral count)
- writeIORef ref old_buf{ bufWPtr = w + count }
- return (newEmptyBuffer raw WriteBuffer sz)
-
- -- else, we have to flush
- else do flushed_buf <- flushWriteBuffer fd (haIsStream handle_) old_buf
-
- let this_buf =
- Buffer{ bufBuf=raw, bufState=WriteBuffer,
- bufRPtr=0, bufWPtr=count, bufSize=sz }
-
- -- if: (a) we don't have to flush, and
- -- (b) size(new buffer) == size(old buffer), and
- -- (c) new buffer is not full,
- -- we can just just swap them over...
- if (not flush && sz == size && count /= sz)
- then do
- writeIORef ref this_buf
- return flushed_buf
-
- -- otherwise, we have to flush the new data too,
- -- and start with a fresh buffer
- else do
- flushWriteBuffer fd (haIsStream handle_) this_buf
- writeIORef ref flushed_buf
- -- if the sizes were different, then allocate
- -- a new buffer of the correct size.
- if sz == size
- then return (newEmptyBuffer raw WriteBuffer sz)
- else allocateBuffer size WriteBuffer
-
- -- release the buffer if necessary
- case buf_ret of
- Buffer{ bufSize=buf_ret_sz, bufBuf=buf_ret_raw } -> do
- if release && buf_ret_sz == size
- then do
- spare_bufs <- readIORef spare_buf_ref
- writeIORef spare_buf_ref
- (BufferListCons buf_ret_raw spare_bufs)
- return buf_ret
- else
- return buf_ret
+-- Primitive catch and throwIO
--- ---------------------------------------------------------------------------
--- Reading/writing sequences of bytes.
+{-
+catchException used to handle the passing around of the state to the
+action and the handler. This turned out to be a bad idea - it meant
+that we had to wrap both arguments in thunks so they could be entered
+as normal (remember IO returns an unboxed pair...).
--- ---------------------------------------------------------------------------
--- hPutBuf
+Now catch# has type
--- | 'hPutBuf' @hdl buf count@ writes @count@ 8-bit bytes from the
--- buffer @buf@ to the handle @hdl@. It returns ().
---
--- This operation may fail with:
---
--- * 'ResourceVanished' if the handle is a pipe or socket, and the
--- reading end is closed. (If this is a POSIX system, and the program
--- has not asked to ignore SIGPIPE, then a SIGPIPE may be delivered
--- instead, whose default action is to terminate the program).
-
-hPutBuf :: Handle -- handle to write to
- -> Ptr a -- address of buffer
- -> Int -- number of bytes of data in buffer
- -> IO ()
-hPutBuf h ptr count = do hPutBuf' h ptr count True; return ()
-
-hPutBufNonBlocking
- :: Handle -- handle to write to
- -> Ptr a -- address of buffer
- -> Int -- number of bytes of data in buffer
- -> IO Int -- returns: number of bytes written
-hPutBufNonBlocking h ptr count = hPutBuf' h ptr count False
-
-hPutBuf':: Handle -- handle to write to
- -> Ptr a -- address of buffer
- -> Int -- number of bytes of data in buffer
- -> Bool -- allow blocking?
- -> IO Int
-hPutBuf' handle ptr count can_block
- | count == 0 = return 0
- | count < 0 = illegalBufferSize handle "hPutBuf" count
- | otherwise =
- wantWritableHandle "hPutBuf" handle $
- \ Handle__{ haFD=fd, haBuffer=ref, haIsStream=is_stream } ->
- bufWrite fd ref is_stream ptr count can_block
-
-bufWrite :: FD -> IORef Buffer -> Bool -> Ptr a -> Int -> Bool -> IO Int
-bufWrite fd ref is_stream ptr count can_block =
- seq count $ seq fd $ do -- strictness hack
- old_buf@Buffer{ bufBuf=old_raw, bufWPtr=w, bufSize=size }
- <- readIORef ref
-
- -- enough room in handle buffer?
- if (size - w > count)
- -- There's enough room in the buffer:
- -- just copy the data in and update bufWPtr.
- then do memcpy_baoff_ptr old_raw (fromIntegral w) ptr (fromIntegral count)
- writeIORef ref old_buf{ bufWPtr = w + count }
- return count
-
- -- else, we have to flush
- else do flushed_buf <- flushWriteBuffer fd is_stream old_buf
- -- TODO: we should do a non-blocking flush here
- writeIORef ref flushed_buf
- -- if we can fit in the buffer, then just loop
- if count < size
- then bufWrite fd ref is_stream ptr count can_block
- else if can_block
- then do writeChunk fd is_stream (castPtr ptr) count
- return count
- else writeChunkNonBlocking fd is_stream ptr count
-
-writeChunk :: FD -> Bool -> Ptr CChar -> Int -> IO ()
-writeChunk fd is_stream ptr bytes0 = loop 0 bytes0
- where
- loop :: Int -> Int -> IO ()
- loop _ bytes | bytes <= 0 = return ()
- loop off bytes = do
- r <- fromIntegral `liftM`
- writeRawBufferPtr "writeChunk" fd is_stream ptr
- off (fromIntegral bytes)
- -- write can't return 0
- loop (off + r) (bytes - r)
-
-writeChunkNonBlocking :: FD -> Bool -> Ptr a -> Int -> IO Int
-writeChunkNonBlocking fd
-#ifndef mingw32_HOST_OS
- _
-#else
- is_stream
-#endif
- ptr bytes0 = loop 0 bytes0
- where
- loop :: Int -> Int -> IO Int
- loop off bytes | bytes <= 0 = return off
- loop off bytes = do
-#ifndef mingw32_HOST_OS
- ssize <- c_write fd (ptr `plusPtr` off) (fromIntegral bytes)
- let r = fromIntegral ssize :: Int
- if (r == -1)
- then do errno <- getErrno
- if (errno == eAGAIN || errno == eWOULDBLOCK)
- then return off
- else throwErrno "writeChunk"
- else loop (off + r) (bytes - r)
-#else
- (ssize, rc) <- asyncWrite (fromIntegral fd)
- (fromIntegral $ fromEnum is_stream)
- (fromIntegral bytes)
- (ptr `plusPtr` off)
- let r = fromIntegral ssize :: Int
- if r == (-1)
- then ioError (errnoToIOError "hPutBufNonBlocking" (Errno (fromIntegral rc)) Nothing Nothing)
- else loop (off + r) (bytes - r)
-#endif
+ catch# :: IO a -> (b -> IO a) -> IO a
--- ---------------------------------------------------------------------------
--- hGetBuf
+(well almost; the compiler doesn't know about the IO newtype so we
+have to work around that in the definition of catchException below).
+-}
--- | 'hGetBuf' @hdl buf count@ reads data from the handle @hdl@
--- into the buffer @buf@ until either EOF is reached or
--- @count@ 8-bit bytes have been read.
--- It returns the number of bytes actually read. This may be zero if
--- EOF was reached before any data was read (or if @count@ is zero).
---
--- 'hGetBuf' never raises an EOF exception, instead it returns a value
--- smaller than @count@.
---
--- If the handle is a pipe or socket, and the writing end
--- is closed, 'hGetBuf' will behave as if EOF was reached.
-
-hGetBuf :: Handle -> Ptr a -> Int -> IO Int
-hGetBuf h ptr count
- | count == 0 = return 0
- | count < 0 = illegalBufferSize h "hGetBuf" count
- | otherwise =
- wantReadableHandle "hGetBuf" h $
- \ Handle__{ haFD=fd, haBuffer=ref, haIsStream=is_stream } -> do
- bufRead fd ref is_stream ptr 0 count
-
--- small reads go through the buffer, large reads are satisfied by
--- taking data first from the buffer and then direct from the file
--- descriptor.
-bufRead :: FD -> IORef Buffer -> Bool -> Ptr a -> Int -> Int -> IO Int
-bufRead fd ref is_stream ptr so_far count =
- seq fd $ seq so_far $ seq count $ do -- strictness hack
- buf@Buffer{ bufBuf=raw, bufWPtr=w, bufRPtr=r, bufSize=sz } <- readIORef ref
- if bufferEmpty buf
- then if count > sz -- small read?
- then do rest <- readChunk fd is_stream ptr count
- return (so_far + rest)
- else do mb_buf <- maybeFillReadBuffer fd True is_stream buf
- case mb_buf of
- Nothing -> return so_far -- got nothing, we're done
- Just buf' -> do
- writeIORef ref buf'
- bufRead fd ref is_stream ptr so_far count
- else do
- let avail = w - r
- if (count == avail)
- then do
- memcpy_ptr_baoff ptr raw (fromIntegral r) (fromIntegral count)
- writeIORef ref buf{ bufWPtr=0, bufRPtr=0 }
- return (so_far + count)
- else do
- if (count < avail)
- then do
- memcpy_ptr_baoff ptr raw (fromIntegral r) (fromIntegral count)
- writeIORef ref buf{ bufRPtr = r + count }
- return (so_far + count)
- else do
-
- memcpy_ptr_baoff ptr raw (fromIntegral r) (fromIntegral avail)
- writeIORef ref buf{ bufWPtr=0, bufRPtr=0 }
- let remaining = count - avail
- so_far' = so_far + avail
- ptr' = ptr `plusPtr` avail
-
- if remaining < sz
- then bufRead fd ref is_stream ptr' so_far' remaining
- else do
-
- rest <- readChunk fd is_stream ptr' remaining
- return (so_far' + rest)
-
-readChunk :: FD -> Bool -> Ptr a -> Int -> IO Int
-readChunk fd is_stream ptr bytes0 = loop 0 bytes0
- where
- loop :: Int -> Int -> IO Int
- loop off bytes | bytes <= 0 = return off
- loop off bytes = do
- r <- fromIntegral `liftM`
- readRawBufferPtr "readChunk" fd is_stream
- (castPtr ptr) off (fromIntegral bytes)
- if r == 0
- then return off
- else loop (off + r) (bytes - r)
-
-
--- | 'hGetBufNonBlocking' @hdl buf count@ reads data from the handle @hdl@
--- into the buffer @buf@ until either EOF is reached, or
--- @count@ 8-bit bytes have been read, or there is no more data available
--- to read immediately.
+catchException :: Exception e => IO a -> (e -> IO a) -> IO a
+catchException (IO io) handler = IO $ catch# io handler'
+ where handler' e = case fromException e of
+ Just e' -> unIO (handler e')
+ Nothing -> raise# e
+
+catchAny :: IO a -> (forall e . Exception e => e -> IO a) -> IO a
+catchAny (IO io) handler = IO $ catch# io handler'
+ where handler' (SomeException e) = unIO (handler e)
+
+-- | A variant of 'throw' that can only be used within the 'IO' monad.
--
--- 'hGetBufNonBlocking' is identical to 'hGetBuf', except that it will
--- never block waiting for data to become available, instead it returns
--- only whatever data is available. To wait for data to arrive before
--- calling 'hGetBufNonBlocking', use 'hWaitForInput'.
+-- Although 'throwIO' has a type that is an instance of the type of 'throw', the
+-- two functions are subtly different:
--
--- If the handle is a pipe or socket, and the writing end
--- is closed, 'hGetBufNonBlocking' will behave as if EOF was reached.
+-- > throw e `seq` x ===> throw e
+-- > throwIO e `seq` x ===> x
--
-hGetBufNonBlocking :: Handle -> Ptr a -> Int -> IO Int
-hGetBufNonBlocking h ptr count
- | count == 0 = return 0
- | count < 0 = illegalBufferSize h "hGetBufNonBlocking" count
- | otherwise =
- wantReadableHandle "hGetBufNonBlocking" h $
- \ Handle__{ haFD=fd, haBuffer=ref, haIsStream=is_stream } -> do
- bufReadNonBlocking fd ref is_stream ptr 0 count
-
-bufReadNonBlocking :: FD -> IORef Buffer -> Bool -> Ptr a -> Int -> Int
- -> IO Int
-bufReadNonBlocking fd ref is_stream ptr so_far count =
- seq fd $ seq so_far $ seq count $ do -- strictness hack
- buf@Buffer{ bufBuf=raw, bufWPtr=w, bufRPtr=r, bufSize=sz } <- readIORef ref
- if bufferEmpty buf
- then if count > sz -- large read?
- then do rest <- readChunkNonBlocking fd is_stream ptr count
- return (so_far + rest)
- else do buf' <- fillReadBufferWithoutBlocking fd is_stream buf
- case buf' of { Buffer{ bufWPtr=w' } ->
- if (w' == 0)
- then return so_far
- else do writeIORef ref buf'
- bufReadNonBlocking fd ref is_stream ptr
- so_far (min count w')
- -- NOTE: new count is min count w'
- -- so we will just copy the contents of the
- -- buffer in the recursive call, and not
- -- loop again.
- }
- else do
- let avail = w - r
- if (count == avail)
- then do
- memcpy_ptr_baoff ptr raw (fromIntegral r) (fromIntegral count)
- writeIORef ref buf{ bufWPtr=0, bufRPtr=0 }
- return (so_far + count)
- else do
- if (count < avail)
- then do
- memcpy_ptr_baoff ptr raw (fromIntegral r) (fromIntegral count)
- writeIORef ref buf{ bufRPtr = r + count }
- return (so_far + count)
- else do
-
- memcpy_ptr_baoff ptr raw (fromIntegral r) (fromIntegral avail)
- writeIORef ref buf{ bufWPtr=0, bufRPtr=0 }
- let remaining = count - avail
- so_far' = so_far + avail
- ptr' = ptr `plusPtr` avail
-
- -- we haven't attempted to read anything yet if we get to here.
- if remaining < sz
- then bufReadNonBlocking fd ref is_stream ptr' so_far' remaining
- else do
-
- rest <- readChunkNonBlocking fd is_stream ptr' remaining
- return (so_far' + rest)
-
-
-readChunkNonBlocking :: FD -> Bool -> Ptr a -> Int -> IO Int
-readChunkNonBlocking fd is_stream ptr bytes = do
- fromIntegral `liftM`
- readRawBufferPtrNoBlock "readChunkNonBlocking" fd is_stream
- (castPtr ptr) 0 (fromIntegral bytes)
-
- -- we don't have non-blocking read support on Windows, so just invoke
- -- the ordinary low-level read which will block until data is available,
- -- but won't wait for the whole buffer to fill.
-
-slurpFile :: FilePath -> IO (Ptr (), Int)
-slurpFile fname = do
- handle <- openFile fname ReadMode
- sz <- hFileSize handle
- if sz > fromIntegral (maxBound::Int) then
- ioError (userError "slurpFile: file too big")
- else do
- let sz_i = fromIntegral sz
- if sz_i == 0 then return (nullPtr, 0) else do
- chunk <- mallocBytes sz_i
- r <- hGetBuf handle chunk sz_i
- hClose handle
- return (chunk, r)
-
--- ---------------------------------------------------------------------------
--- memcpy wrappers
-
-foreign import ccall unsafe "__hscore_memcpy_src_off"
- memcpy_ba_baoff :: RawBuffer -> RawBuffer -> CInt -> CSize -> IO (Ptr ())
-foreign import ccall unsafe "__hscore_memcpy_src_off"
- memcpy_ptr_baoff :: Ptr a -> RawBuffer -> CInt -> CSize -> IO (Ptr ())
-foreign import ccall unsafe "__hscore_memcpy_dst_off"
- memcpy_baoff_ba :: RawBuffer -> CInt -> RawBuffer -> CSize -> IO (Ptr ())
-foreign import ccall unsafe "__hscore_memcpy_dst_off"
- memcpy_baoff_ptr :: RawBuffer -> CInt -> Ptr a -> CSize -> IO (Ptr ())
+-- The first example will cause the exception @e@ to be raised,
+-- whereas the second one won\'t. In fact, 'throwIO' will only cause
+-- an exception to be raised when it is used within the 'IO' monad.
+-- The 'throwIO' variant should be used in preference to 'throw' to
+-- raise an exception within the 'IO' monad because it guarantees
+-- ordering with respect to other 'IO' operations, whereas 'throw'
+-- does not.
+throwIO :: Exception e => e -> IO a
+throwIO e = IO (raiseIO# (toException e))
------------------------------------------------------------------------------
--- Internal Utils
-
-illegalBufferSize :: Handle -> String -> Int -> IO a
-illegalBufferSize handle fn sz =
- ioException (IOError (Just handle)
- InvalidArgument fn
- ("illegal buffer size " ++ showsPrec 9 sz [])
- Nothing Nothing)
+-- -----------------------------------------------------------------------------
+-- Controlling asynchronous exception delivery
+
+-- | Applying 'block' to a computation will
+-- execute that computation with asynchronous exceptions
+-- /blocked/. That is, any thread which
+-- attempts to raise an exception in the current thread with 'Control.Exception.throwTo' will be
+-- blocked until asynchronous exceptions are enabled again. There\'s
+-- no need to worry about re-enabling asynchronous exceptions; that is
+-- done automatically on exiting the scope of
+-- 'block'.
+--
+-- Threads created by 'Control.Concurrent.forkIO' inherit the blocked
+-- state from the parent; that is, to start a thread in blocked mode,
+-- use @block $ forkIO ...@. This is particularly useful if you need to
+-- establish an exception handler in the forked thread before any
+-- asynchronous exceptions are received.
+block :: IO a -> IO a
+
+-- | To re-enable asynchronous exceptions inside the scope of
+-- 'block', 'unblock' can be
+-- used. It scopes in exactly the same way, so on exit from
+-- 'unblock' asynchronous exception delivery will
+-- be disabled again.
+unblock :: IO a -> IO a
+
+block (IO io) = IO $ blockAsyncExceptions# io
+unblock (IO io) = IO $ unblockAsyncExceptions# io
+
+-- | returns True if asynchronous exceptions are blocked in the
+-- current thread.
+blocked :: IO Bool
+blocked = IO $ \s -> case asyncExceptionsBlocked# s of
+ (# s', i #) -> (# s', i /=# 0# #)
+
+onException :: IO a -> IO b -> IO a
+onException io what = io `catchException` \e -> do what
+ throw (e :: SomeException)
+
+finally :: IO a -- ^ computation to run first
+ -> IO b -- ^ computation to run afterward (even if an exception
+ -- was raised)
+ -> IO a -- returns the value from the first computation
+a `finally` sequel =
+ block (do
+ r <- unblock a `onException` sequel
+ sequel
+ return r
+ )
+
+-- | Forces its argument to be evaluated to weak head normal form when
+-- the resultant 'IO' action is executed. It can be used to order
+-- evaluation with respect to other 'IO' operations; its semantics are
+-- given by
+--
+-- > evaluate x `seq` y ==> y
+-- > evaluate x `catch` f ==> (return $! x) `catch` f
+-- > evaluate x >>= f ==> (return $! x) >>= f
+--
+-- /Note:/ the first equation implies that @(evaluate x)@ is /not/ the
+-- same as @(return $! x)@. A correct definition is
+--
+-- > evaluate x = (return $! x) >>= return
+--
+evaluate :: a -> IO a
+evaluate a = IO $ \s -> case a `seq` () of () -> (# s, a #)
+ -- NB. can't write
+ -- a `seq` (# s, a #)
+ -- because we can't have an unboxed tuple as a function argument
projects / ghc-base.git / blobdiff