module GHC.IOBase(
IO(..), unIO, failIO, liftIO, bindIO, thenIO, returnIO,
unsafePerformIO, unsafeInterleaveIO,
+ unsafeDupablePerformIO, unsafeDupableInterleaveIO,
+ noDuplicate,
-- To and from from ST
- stToIO, ioToST, unsafeIOToST,
+ stToIO, ioToST, unsafeIOToST, unsafeSTToIO,
-- References
IORef(..), newIORef, readIORef, writeIORef,
-- Handles, file descriptors,
FilePath,
Handle(..), Handle__(..), HandleType(..), IOMode(..), FD,
- isReadableHandleType, isWritableHandleType, showHandle,
+ isReadableHandleType, isWritableHandleType, isReadWriteHandleType, showHandle,
-- Buffers
Buffer(..), RawBuffer, BufferState(..), BufferList(..), BufferMode(..),
import GHC.Show
import GHC.List
import GHC.Read
+import Foreign.C.Types (CInt)
#ifndef __HADDOCK__
-import {-# SOURCE #-} Data.Dynamic
+import {-# SOURCE #-} Data.Typeable ( showsTypeRep )
+import {-# SOURCE #-} Data.Dynamic ( Dynamic, dynTypeRep )
#endif
-- ---------------------------------------------------------------------------
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)
+
-- ---------------------------------------------------------------------------
-- Unsafe IO operations
possible to write @coerce :: a -> b@ with the
help of 'unsafePerformIO'. So be careful!
-}
-{-# NOINLINE unsafePerformIO #-}
unsafePerformIO :: IO a -> a
-unsafePerformIO (IO m) = case m realWorld# of (# _, r #) -> r
+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 unsafePerformIO? See the comment with
+-- 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
-}
{-# INLINE unsafeInterleaveIO #-}
unsafeInterleaveIO :: IO a -> IO a
-unsafeInterleaveIO (IO m)
+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 #))
--- 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.
+{-|
+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', () #)
-- ---------------------------------------------------------------------------
-- Handle type
(DuplexHandle _ h1 _) == (DuplexHandle _ h2 _) = h1 == h2
_ == _ = False
-type FD = Int -- XXX ToDo: should be CInt
+type FD = CInt
data Handle__
= Handle__ {
haFD :: !FD, -- file descriptor
haType :: HandleType, -- type (read/write/append etc.)
haIsBin :: Bool, -- binary mode?
- haIsStream :: Bool, -- is this a stream handle?
+ haIsStream :: Bool, -- Windows : is this a socket?
+ -- Unix : is O_NONBLOCK set?
haBufferMode :: BufferMode, -- buffer contains read/write data?
haBuffer :: !(IORef Buffer), -- the current buffer
haBuffers :: !(IORef BufferList), -- spare buffers
isWritableHandleType ReadWriteHandle = True
isWritableHandleType _ = False
+isReadWriteHandleType ReadWriteHandle{} = True
+isReadWriteHandleType _ = False
+
-- | 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.
-- ^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.
+ | NestedAtomically
+ -- ^The runtime detected an attempt to nest one STM transaction
+ -- inside another one, presumably due to the use of
+ -- 'unsafePeformIO' with 'atomically'.
| Deadlock
-- ^There are no runnable threads, so the program is
-- deadlocked. The 'Deadlock' exception is
showsPrec _ (RecConError err) = showString err
showsPrec _ (RecUpdError err) = showString err
showsPrec _ (AssertionFailed err) = showString err
- showsPrec _ (DynException _err) = showString "unknown exception"
+ showsPrec _ (DynException err) = showString "exception :: " . showsTypeRep (dynTypeRep err)
showsPrec _ (AsyncException e) = shows e
showsPrec _ (BlockedOnDeadMVar) = showString "thread blocked indefinitely"
showsPrec _ (BlockedIndefinitely) = showString "thread blocked indefinitely"
+ showsPrec _ (NestedAtomically) = showString "Control.Concurrent.STM.atomically was nested"
showsPrec _ (NonTermination) = showString "<<loop>>"
showsPrec _ (Deadlock) = showString "<<deadlock>>"
AsyncException e1 == AsyncException e2 = e1 == e2
BlockedOnDeadMVar == BlockedOnDeadMVar = True
NonTermination == NonTermination = True
+ NestedAtomically == NestedAtomically = True
Deadlock == Deadlock = True
_ == _ = False
-- Although 'throwIO' has a type that is an instance of the type of 'throw', the
-- two functions are subtly different:
--
--- > throw e `seq` return () ===> throw e
--- > throwIO e `seq` return () ===> return ()
+-- > throw e `seq` x ===> throw e
+-- > throwIO e `seq` x ===> x
--
-- The first example will cause the exception @e@ to be raised,
-- whereas the second one won\'t. In fact, 'throwIO' will only cause
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