X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=GHC%2FIOBase.lhs;h=233148b0eaffffa011ccb91673cacb6e5820d0c8;hb=28fb12f4e4059674e9396fc76a2783e0ae8798cd;hp=93a02b7263203bdaa6b1ec762a8af945b24b3079;hpb=b847c4decf42a5bc503c38bcc74a8d3c5fbf35eb;p=ghc-base.git diff --git a/GHC/IOBase.lhs b/GHC/IOBase.lhs index 93a02b7..233148b 100644 --- a/GHC/IOBase.lhs +++ b/GHC/IOBase.lhs @@ -1,5 +1,5 @@ \begin{code} -{-# OPTIONS -fno-implicit-prelude #-} +{-# OPTIONS_GHC -fno-implicit-prelude #-} ----------------------------------------------------------------------------- -- | -- Module : GHC.IOBase @@ -112,13 +112,22 @@ returnIO x = IO (\ s -> (# s, x #)) -- --------------------------------------------------------------------------- -- Coercions between IO and ST ---stToIO :: (forall s. ST s a) -> IO a +-- | 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 +-- +unsafeIOToST :: IO a -> ST s a +unsafeIOToST (IO io) = ST $ \ s -> (unsafeCoerce# io) s + -- --------------------------------------------------------------------------- -- Unsafe IO operations @@ -164,7 +173,7 @@ It is less well known that > > main = do > writeIORef test [42] -> bang \<- readIORef test +> bang <- readIORef test > print (bang :: [Char]) This program will core dump. This problem with polymorphic references @@ -178,13 +187,19 @@ help of 'unsafePerformIO'. So be careful! unsafePerformIO :: IO a -> a unsafePerformIO (IO m) = case m realWorld# of (# _, r #) -> r +-- Why do we NOINLINE unsafePerformIO? 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. + {-| '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'. -} -{-# NOINLINE unsafeInterleaveIO #-} +{-# INLINE unsafeInterleaveIO #-} unsafeInterleaveIO :: IO a -> IO a unsafeInterleaveIO (IO m) = IO ( \ s -> let @@ -192,6 +207,10 @@ unsafeInterleaveIO (IO m) in (# s, r #)) +-- 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. + -- --------------------------------------------------------------------------- -- Handle type @@ -247,6 +266,15 @@ instance Eq (MVar a) where -- enough information to identify the handle for debugging. A handle is -- equal according to '==' only to itself; no attempt -- is made to compare the internal state of different handles for equality. +-- +-- GHC note: a 'Handle' will be automatically closed when the garbage +-- collector detects that it has become unreferenced by the program. +-- However, relying on this behaviour is not generally recommended: +-- the garbage collector is unpredictable. If possible, use explicit +-- an explicit 'hClose' to close 'Handle's when they are no longer +-- required. GHC does not currently attempt to free up file +-- descriptors when they have run out, it is your responsibility to +-- ensure that this doesn't happen. data Handle = FileHandle -- A normal handle to a file @@ -396,7 +424,7 @@ type FilePath = String -- but not less frequently, than specified above. -- The output buffer is emptied as soon as it has been written out. -- --- Similarly, input occurs according to the buffer mode for handle {\em hdl}. +-- Similarly, input occurs according to the buffer mode for the handle: -- -- * /line-buffering/: when the buffer for the handle is not empty, -- the next item is obtained from the buffer; otherwise, when the @@ -408,8 +436,8 @@ type FilePath = String -- the next block of data is read into the buffer. -- -- * /no-buffering/: the next input item is read and returned. --- The 'hLookAhead' operation implies that even a no-buffered handle --- may require a one-character buffer. +-- The 'System.IO.hLookAhead' operation implies that even a no-buffered +-- handle may require a one-character buffer. -- -- The default buffering mode when a handle is opened is -- implementation-dependent and may depend on the file system object @@ -518,7 +546,8 @@ showHandle file = showString "{handle: " . showString file . showString "}" -- |The type of exceptions. Every kind of system-generated exception -- has a constructor in the 'Exception' type, and values of other -- types may be injected into 'Exception' by coercing them to --- 'Dynamic' (see the section on Dynamic Exceptions: "Control.Exception\#DynamicExceptions"). +-- 'Data.Dynamic.Dynamic' (see the section on Dynamic Exceptions: +-- "Control.Exception\#DynamicExceptions"). data Exception = ArithException ArithException -- ^Exceptions raised by arithmetic @@ -537,8 +566,12 @@ data Exception -- ^Asynchronous exceptions (see section on Asynchronous Exceptions: "Control.Exception\#AsynchronousExceptions"). | BlockedOnDeadMVar -- ^The current thread was executing a call to - -- 'takeMVar' that could never return, because there are no other - -- references to this 'MVar'. + -- 'Control.Concurrent.MVar.takeMVar' that could never return, + -- because there are no other references to this 'MVar'. + | BlockedIndefinitely + -- ^The current thread was waiting to retry an atomic memory transaction + -- that could never become possible to complete because there are no other + -- threads referring to any of teh TVars involved. | Deadlock -- ^There are no runnable threads, so the program is -- deadlocked. The 'Deadlock' exception is @@ -620,7 +653,7 @@ data AsyncException -- * GHC currently does not throw 'HeapOverflow' exceptions. | ThreadKilled -- ^This exception is raised by another thread - -- calling 'killThread', or by the system + -- calling 'Control.Concurrent.killThread', or by the system -- if it needs to terminate the thread for some -- reason. deriving (Eq, Ord) @@ -676,6 +709,7 @@ instance Show Exception where showsPrec _ (DynException _err) = showString "unknown exception" showsPrec _ (AsyncException e) = shows e showsPrec _ (BlockedOnDeadMVar) = showString "thread blocked indefinitely" + showsPrec _ (BlockedIndefinitely) = showString "thread blocked indefinitely" showsPrec _ (NonTermination) = showString "<>" showsPrec _ (Deadlock) = showString "<>" @@ -701,18 +735,17 @@ instance Eq Exception where -- ----------------------------------------------------------------------------- -- The ExitCode type --- The `ExitCode' type defines the exit codes that a program --- can return. `ExitSuccess' indicates successful termination; --- and `ExitFailure code' indicates program failure --- with value `code'. The exact interpretation of `code' --- is operating-system dependent. In particular, some values of --- `code' may be prohibited (e.g. 0 on a POSIX-compliant system). - -- We need it here because it is used in ExitException in the -- Exception datatype (above). -data ExitCode = ExitSuccess | ExitFailure Int - deriving (Eq, Ord, Read, Show) +data ExitCode + = ExitSuccess -- ^ indicates successful termination; + | ExitFailure Int + -- ^ indicates program failure with an exit code. + -- The exact interpretation of the code is + -- operating-system dependent. In particular, some values + -- may be prohibited (e.g. 0 on a POSIX-compliant system). + deriving (Eq, Ord, Read, Show) -- -------------------------------------------------------------------------- -- Primitive throw @@ -743,13 +776,18 @@ throwIO err = IO $ raiseIO# err ioException :: IOException -> IO a ioException err = IO $ raiseIO# (IOException err) +-- | Raise an 'IOError' in the 'IO' monad. ioError :: IOError -> IO a ioError = ioException -- --------------------------------------------------------------------------- -- IOError type --- | The Haskell 98 type for exceptions in the @IO@ monad. +-- | The Haskell 98 type for exceptions in the 'IO' monad. +-- Any I\/O operation may raise an 'IOError' instead of returning a result. +-- For a more general type of exception, including also those that arise +-- in pure code, see 'Control.Exception.Exception'. +-- -- In Haskell 98, this is an opaque type. type IOError = IOException @@ -771,6 +809,7 @@ instance Eq IOException where (IOError h1 e1 loc1 str1 fn1) == (IOError h2 e2 loc2 str2 fn2) = e1==e2 && str1==str2 && h1==h2 && loc1==loc2 && fn1==fn2 +-- | An abstract type that contains a value for each variant of 'IOError'. data IOErrorType -- Haskell 98: = AlreadyExists @@ -826,6 +865,14 @@ instance Show IOErrorType where UnsupportedOperation -> "unsupported operation" DynIOError{} -> "unknown IO error" +-- | Construct an 'IOError' value with a string describing the error. +-- The 'fail' method of the 'IO' instance of the 'Monad' class raises a +-- 'userError', thus: +-- +-- > instance Monad IO where +-- > ... +-- > fail s = ioError (userError s) +-- userError :: String -> IOError userError str = IOError Nothing UserError "" str Nothing