1 -----------------------------------------------------------------------------
3 -- Module : Control.Concurrent.MVar
4 -- Copyright : (c) The University of Glasgow 2001
5 -- License : BSD-style (see the file libraries/base/LICENSE)
7 -- Maintainer : libraries@haskell.org
8 -- Stability : experimental
9 -- Portability : non-portable (concurrency)
11 -- Synchronising variables
13 -----------------------------------------------------------------------------
15 module Control.Concurrent.MVar
19 , newEmptyMVar -- :: IO (MVar a)
20 , newMVar -- :: a -> IO (MVar a)
21 , takeMVar -- :: MVar a -> IO a
22 , putMVar -- :: MVar a -> a -> IO ()
23 , readMVar -- :: MVar a -> IO a
24 , swapMVar -- :: MVar a -> a -> IO a
25 , tryTakeMVar -- :: MVar a -> IO (Maybe a)
26 , tryPutMVar -- :: MVar a -> a -> IO Bool
27 , isEmptyMVar -- :: MVar a -> IO Bool
28 , withMVar -- :: MVar a -> (a -> IO b) -> IO b
29 , modifyMVar_ -- :: MVar a -> (a -> IO a) -> IO ()
30 , modifyMVar -- :: MVar a -> (a -> IO (a,b)) -> IO b
32 , addMVarFinalizer -- :: MVar a -> IO () -> IO ()
37 import Hugs.ConcBase ( MVar, newEmptyMVar, newMVar, takeMVar, putMVar,
38 tryTakeMVar, tryPutMVar, isEmptyMVar,
40 import Hugs.Exception ( throwIO )
43 #ifdef __GLASGOW_HASKELL__
44 import GHC.Conc ( MVar, newEmptyMVar, newMVar, takeMVar, putMVar,
45 tryTakeMVar, tryPutMVar, isEmptyMVar, addMVarFinalizer
50 import Control.Exception as Exception
53 -- This is as close as Hugs gets to providing throw
54 throw :: Exception -> IO a
59 This is a combination of 'takeMVar' and 'putMVar'; ie. it takes the value
60 from the 'MVar', puts it back, and also returns it.
62 readMVar :: MVar a -> IO a
69 -- |Swap the contents of an 'MVar' for a new value.
70 swapMVar :: MVar a -> a -> IO a
78 'withMVar' is a safe wrapper for operating on the contents of an
79 'MVar'. This operation is exception-safe: it will replace the
80 original contents of the 'MVar' if an exception is raised (see
83 withMVar :: MVar a -> (a -> IO b) -> IO b
87 b <- Exception.catch (unblock (io a))
88 (\e -> do putMVar m a; throw e)
93 A safe wrapper for modifying the contents of an 'MVar'. Like 'withMVar',
94 'modifyMVar' will replace the original contents of the 'MVar' if an
95 exception is raised during the operation.
97 modifyMVar_ :: MVar a -> (a -> IO a) -> IO ()
101 a' <- Exception.catch (unblock (io a))
102 (\e -> do putMVar m a; throw e)
106 A slight variation on 'modifyMVar_' that allows a value to be
107 returned (@b@) in addition to the modified value of the 'MVar'.
109 modifyMVar :: MVar a -> (a -> IO (a,b)) -> IO b
113 (a',b) <- Exception.catch (unblock (io a))
114 (\e -> do putMVar m a; throw e)