+{-# LANGUAGE CPP #-}
+
-----------------------------------------------------------------------------
-- |
-- Module : Control.Concurrent.Chan
-- Copyright : (c) The University of Glasgow 2001
--- License : BSD-style (see the file libraries/core/LICENSE)
+-- License : BSD-style (see the file libraries/base/LICENSE)
--
-- Maintainer : libraries@haskell.org
-- Stability : experimental
--- Portability : non-portable
+-- Portability : non-portable (concurrency)
--
--- Standard, unbounded channel abstraction.
+-- Unbounded channels.
--
-----------------------------------------------------------------------------
module Control.Concurrent.Chan
- ( Chan -- abstract
-
- -- creator
- , newChan -- :: IO (Chan a)
-
- -- operators
- , writeChan -- :: Chan a -> a -> IO ()
- , readChan -- :: Chan a -> IO a
- , dupChan -- :: Chan a -> IO (Chan a)
- , unGetChan -- :: Chan a -> a -> IO ()
-
- , isEmptyChan -- :: Chan a -> IO Bool
-
- -- stream interface
- , getChanContents -- :: Chan a -> IO [a]
- , writeList2Chan -- :: Chan a -> [a] -> IO ()
-
- ) where
+ (
+ -- * The 'Chan' type
+ Chan, -- abstract
+
+ -- * Operations
+ newChan, -- :: IO (Chan a)
+ writeChan, -- :: Chan a -> a -> IO ()
+ readChan, -- :: Chan a -> IO a
+ dupChan, -- :: Chan a -> IO (Chan a)
+ unGetChan, -- :: Chan a -> a -> IO ()
+ isEmptyChan, -- :: Chan a -> IO Bool
+
+ -- * Stream interface
+ getChanContents, -- :: Chan a -> IO [a]
+ writeList2Chan, -- :: Chan a -> [a] -> IO ()
+ ) where
import Prelude
-import System.IO.Unsafe ( unsafeInterleaveIO )
+import System.IO.Unsafe ( unsafeInterleaveIO )
import Control.Concurrent.MVar
+import Data.Typeable
+
+#include "Typeable.h"
-- A channel is represented by two @MVar@s keeping track of the two ends
-- of the channel contents,i.e., the read- and write ends. Empty @MVar@s
-- are used to handle consumers trying to read from an empty channel.
+-- |'Chan' is an abstract type representing an unbounded FIFO channel.
data Chan a
= Chan (MVar (Stream a))
(MVar (Stream a))
+ deriving Eq
+
+INSTANCE_TYPEABLE1(Chan,chanTc,"Chan")
type Stream a = MVar (ChItem a)
-- @newChan@ sets up the read and write end of a channel by initialising
-- these two @MVar@s with an empty @MVar@.
+-- |Build and returns a new instance of 'Chan'.
newChan :: IO (Chan a)
newChan = do
hole <- newEmptyMVar
- read <- newMVar hole
- write <- newMVar hole
- return (Chan read write)
+ readVar <- newMVar hole
+ writeVar <- newMVar hole
+ return (Chan readVar writeVar)
-- To put an element on a channel, a new hole at the write end is created.
-- What was previously the empty @MVar@ at the back of the channel is then
-- filled in with a new stream element holding the entered value and the
-- new hole.
+-- |Write a value to a 'Chan'.
writeChan :: Chan a -> a -> IO ()
-writeChan (Chan _read write) val = do
+writeChan (Chan _ writeVar) val = do
new_hole <- newEmptyMVar
- modifyMVar_ write $ \old_hole -> do
+ modifyMVar_ writeVar $ \old_hole -> do
putMVar old_hole (ChItem val new_hole)
return new_hole
+-- |Read the next value from the 'Chan'.
readChan :: Chan a -> IO a
-readChan (Chan read _write) = do
- modifyMVar read $ \read_end -> do
+readChan (Chan readVar _) = do
+ modifyMVar readVar $ \read_end -> do
(ChItem val new_read_end) <- readMVar read_end
- -- Use readMVar here, not takeMVar,
- -- else dupChan doesn't work
+ -- Use readMVar here, not takeMVar,
+ -- else dupChan doesn't work
return (new_read_end, val)
+-- |Duplicate a 'Chan': the duplicate channel begins empty, but data written to
+-- either channel from then on will be available from both. Hence this creates
+-- a kind of broadcast channel, where data written by anyone is seen by
+-- everyone else.
+--
+-- (Note that a duplicated channel is not equal to its original.
+-- So: @fmap (c /=) $ dupChan c@ returns @True@ for all @c@.)
dupChan :: Chan a -> IO (Chan a)
-dupChan (Chan _read write) = do
- hole <- readMVar write
- new_read <- newMVar hole
- return (Chan new_read write)
+dupChan (Chan _ writeVar) = do
+ hole <- readMVar writeVar
+ newReadVar <- newMVar hole
+ return (Chan newReadVar writeVar)
+-- |Put a data item back onto a channel, where it will be the next item read.
unGetChan :: Chan a -> a -> IO ()
-unGetChan (Chan read _write) val = do
+unGetChan (Chan readVar _) val = do
new_read_end <- newEmptyMVar
- modifyMVar_ read $ \read_end -> do
+ modifyMVar_ readVar $ \read_end -> do
putMVar new_read_end (ChItem val read_end)
return new_read_end
+{-# DEPRECATED unGetChan "if you need this operation, use Control.Concurrent.STM.TChan instead. See http://hackage.haskell.org/trac/ghc/ticket/4154 for details" #-}
+-- |Returns 'True' if the supplied 'Chan' is empty.
isEmptyChan :: Chan a -> IO Bool
-isEmptyChan (Chan read write) = do
- withMVar read $ \r -> do
- w <- readMVar write
+isEmptyChan (Chan readVar writeVar) = do
+ withMVar readVar $ \r -> do
+ w <- readMVar writeVar
let eq = r == w
eq `seq` return eq
+{-# DEPRECATED isEmptyChan "if you need this operation, use Control.Concurrent.STM.TChan instead. See http://hackage.haskell.org/trac/ghc/ticket/4154 for details" #-}
-- Operators for interfacing with functional streams.
+-- |Return a lazy list representing the contents of the supplied
+-- 'Chan', much like 'System.IO.hGetContents'.
getChanContents :: Chan a -> IO [a]
getChanContents ch
= unsafeInterleaveIO (do
- x <- readChan ch
- xs <- getChanContents ch
- return (x:xs)
+ x <- readChan ch
+ xs <- getChanContents ch
+ return (x:xs)
)
--------------
+-- |Write an entire list of items to a 'Chan'.
writeList2Chan :: Chan a -> [a] -> IO ()
writeList2Chan ch ls = sequence_ (map (writeChan ch) ls)
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