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<pre><a name="line-1"></a><span class='hs-comment'>-----------------------------------------------------------------------------</span>
<a name="line-2"></a><span class='hs-comment'>-- |</span>
<a name="line-3"></a><span class='hs-comment'>-- Module : Control.Concurrent.Chan</span>
<a name="line-4"></a><span class='hs-comment'>-- Copyright : (c) The University of Glasgow 2001</span>
<a name="line-5"></a><span class='hs-comment'>-- License : BSD-style (see the file libraries/base/LICENSE)</span>
<a name="line-6"></a><span class='hs-comment'>-- </span>
<a name="line-7"></a><span class='hs-comment'>-- Maintainer : libraries@haskell.org</span>
<a name="line-8"></a><span class='hs-comment'>-- Stability : experimental</span>
<a name="line-9"></a><span class='hs-comment'>-- Portability : non-portable (concurrency)</span>
<a name="line-10"></a><span class='hs-comment'>--</span>
<a name="line-11"></a><span class='hs-comment'>-- Unbounded channels.</span>
<a name="line-12"></a><span class='hs-comment'>--</span>
<a name="line-13"></a><span class='hs-comment'>-----------------------------------------------------------------------------</span>
<a name="line-14"></a>
<a name="line-15"></a><span class='hs-keyword'>module</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Concurrent</span><span class='hs-varop'>.</span><span class='hs-conid'>Chan</span>
<a name="line-16"></a> <span class='hs-layout'>(</span>
<a name="line-17"></a> <span class='hs-comment'>-- * The 'Chan' type</span>
<a name="line-18"></a> <span class='hs-conid'>Chan</span><span class='hs-layout'>,</span> <span class='hs-comment'>-- abstract</span>
<a name="line-19"></a>
<a name="line-20"></a> <span class='hs-comment'>-- * Operations</span>
<a name="line-21"></a> <span class='hs-varid'>newChan</span><span class='hs-layout'>,</span> <span class='hs-comment'>-- :: IO (Chan a)</span>
<a name="line-22"></a> <span class='hs-varid'>writeChan</span><span class='hs-layout'>,</span> <span class='hs-comment'>-- :: Chan a -> a -> IO ()</span>
<a name="line-23"></a> <span class='hs-varid'>readChan</span><span class='hs-layout'>,</span> <span class='hs-comment'>-- :: Chan a -> IO a</span>
<a name="line-24"></a> <span class='hs-varid'>dupChan</span><span class='hs-layout'>,</span> <span class='hs-comment'>-- :: Chan a -> IO (Chan a)</span>
<a name="line-25"></a> <span class='hs-varid'>unGetChan</span><span class='hs-layout'>,</span> <span class='hs-comment'>-- :: Chan a -> a -> IO ()</span>
<a name="line-26"></a> <span class='hs-varid'>isEmptyChan</span><span class='hs-layout'>,</span> <span class='hs-comment'>-- :: Chan a -> IO Bool</span>
<a name="line-27"></a>
<a name="line-28"></a> <span class='hs-comment'>-- * Stream interface</span>
<a name="line-29"></a> <span class='hs-varid'>getChanContents</span><span class='hs-layout'>,</span> <span class='hs-comment'>-- :: Chan a -> IO [a]</span>
<a name="line-30"></a> <span class='hs-varid'>writeList2Chan</span><span class='hs-layout'>,</span> <span class='hs-comment'>-- :: Chan a -> [a] -> IO ()</span>
<a name="line-31"></a> <span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-32"></a>
<a name="line-33"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Prelude</span>
<a name="line-34"></a>
<a name="line-35"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>System</span><span class='hs-varop'>.</span><span class='hs-conid'>IO</span><span class='hs-varop'>.</span><span class='hs-conid'>Unsafe</span> <span class='hs-layout'>(</span> <span class='hs-varid'>unsafeInterleaveIO</span> <span class='hs-layout'>)</span>
<a name="line-36"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Concurrent</span><span class='hs-varop'>.</span><span class='hs-conid'>MVar</span>
<a name="line-37"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Typeable</span>
<a name="line-38"></a>
<a name="line-39"></a><span class='hs-cpp'>#include "Typeable.h"</span>
<a name="line-40"></a>
<a name="line-41"></a><span class='hs-comment'>-- A channel is represented by two @MVar@s keeping track of the two ends</span>
<a name="line-42"></a><span class='hs-comment'>-- of the channel contents,i.e., the read- and write ends. Empty @MVar@s</span>
<a name="line-43"></a><span class='hs-comment'>-- are used to handle consumers trying to read from an empty channel.</span>
<a name="line-44"></a>
<a name="line-45"></a><a name="Chan"></a><span class='hs-comment'>-- |'Chan' is an abstract type representing an unbounded FIFO channel.</span>
<a name="line-46"></a><a name="Chan"></a><span class='hs-keyword'>data</span> <span class='hs-conid'>Chan</span> <span class='hs-varid'>a</span>
<a name="line-47"></a> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Chan</span> <span class='hs-layout'>(</span><span class='hs-conid'>MVar</span> <span class='hs-layout'>(</span><span class='hs-conid'>Stream</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span>
<a name="line-48"></a> <span class='hs-layout'>(</span><span class='hs-conid'>MVar</span> <span class='hs-layout'>(</span><span class='hs-conid'>Stream</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span>
<a name="line-49"></a>
<a name="line-50"></a><span class='hs-conid'>INSTANCE_TYPEABLE1</span><span class='hs-layout'>(</span><span class='hs-conid'>Chan</span><span class='hs-layout'>,</span><span class='hs-varid'>chanTc</span><span class='hs-layout'>,</span><span class='hs-str'>"Chan"</span><span class='hs-layout'>)</span>
<a name="line-51"></a>
<a name="line-52"></a><a name="Stream"></a><span class='hs-keyword'>type</span> <span class='hs-conid'>Stream</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>MVar</span> <span class='hs-layout'>(</span><span class='hs-conid'>ChItem</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span>
<a name="line-53"></a>
<a name="line-54"></a><a name="ChItem"></a><span class='hs-keyword'>data</span> <span class='hs-conid'>ChItem</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ChItem</span> <span class='hs-varid'>a</span> <span class='hs-layout'>(</span><span class='hs-conid'>Stream</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span>
<a name="line-55"></a>
<a name="line-56"></a><span class='hs-comment'>-- See the Concurrent Haskell paper for a diagram explaining the</span>
<a name="line-57"></a><span class='hs-comment'>-- how the different channel operations proceed.</span>
<a name="line-58"></a>
<a name="line-59"></a><span class='hs-comment'>-- @newChan@ sets up the read and write end of a channel by initialising</span>
<a name="line-60"></a><span class='hs-comment'>-- these two @MVar@s with an empty @MVar@.</span>
<a name="line-61"></a>
<a name="line-62"></a><a name="newChan"></a><span class='hs-comment'>-- |Build and returns a new instance of 'Chan'.</span>
<a name="line-63"></a><span class='hs-definition'>newChan</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>IO</span> <span class='hs-layout'>(</span><span class='hs-conid'>Chan</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span>
<a name="line-64"></a><span class='hs-definition'>newChan</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-65"></a> <span class='hs-varid'>hole</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>newEmptyMVar</span>
<a name="line-66"></a> <span class='hs-varid'>readVar</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>newMVar</span> <span class='hs-varid'>hole</span>
<a name="line-67"></a> <span class='hs-varid'>writeVar</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>newMVar</span> <span class='hs-varid'>hole</span>
<a name="line-68"></a> <span class='hs-varid'>return</span> <span class='hs-layout'>(</span><span class='hs-conid'>Chan</span> <span class='hs-varid'>readVar</span> <span class='hs-varid'>writeVar</span><span class='hs-layout'>)</span>
<a name="line-69"></a>
<a name="line-70"></a><span class='hs-comment'>-- To put an element on a channel, a new hole at the write end is created.</span>
<a name="line-71"></a><span class='hs-comment'>-- What was previously the empty @MVar@ at the back of the channel is then</span>
<a name="line-72"></a><span class='hs-comment'>-- filled in with a new stream element holding the entered value and the</span>
<a name="line-73"></a><span class='hs-comment'>-- new hole.</span>
<a name="line-74"></a>
<a name="line-75"></a><a name="writeChan"></a><span class='hs-comment'>-- |Write a value to a 'Chan'.</span>
<a name="line-76"></a><span class='hs-definition'>writeChan</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Chan</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-conid'>()</span>
<a name="line-77"></a><span class='hs-definition'>writeChan</span> <span class='hs-layout'>(</span><span class='hs-conid'>Chan</span> <span class='hs-keyword'>_</span> <span class='hs-varid'>writeVar</span><span class='hs-layout'>)</span> <span class='hs-varid'>val</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-78"></a> <span class='hs-varid'>new_hole</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>newEmptyMVar</span>
<a name="line-79"></a> <span class='hs-varid'>modifyMVar_</span> <span class='hs-varid'>writeVar</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>old_hole</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyword'>do</span>
<a name="line-80"></a> <span class='hs-varid'>putMVar</span> <span class='hs-varid'>old_hole</span> <span class='hs-layout'>(</span><span class='hs-conid'>ChItem</span> <span class='hs-varid'>val</span> <span class='hs-varid'>new_hole</span><span class='hs-layout'>)</span>
<a name="line-81"></a> <span class='hs-varid'>return</span> <span class='hs-varid'>new_hole</span>
<a name="line-82"></a>
<a name="line-83"></a><a name="readChan"></a><span class='hs-comment'>-- |Read the next value from the 'Chan'.</span>
<a name="line-84"></a><span class='hs-definition'>readChan</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Chan</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-varid'>a</span>
<a name="line-85"></a><span class='hs-definition'>readChan</span> <span class='hs-layout'>(</span><span class='hs-conid'>Chan</span> <span class='hs-varid'>readVar</span> <span class='hs-keyword'>_</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-86"></a> <span class='hs-varid'>modifyMVar</span> <span class='hs-varid'>readVar</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>read_end</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyword'>do</span>
<a name="line-87"></a> <span class='hs-layout'>(</span><span class='hs-conid'>ChItem</span> <span class='hs-varid'>val</span> <span class='hs-varid'>new_read_end</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>readMVar</span> <span class='hs-varid'>read_end</span>
<a name="line-88"></a> <span class='hs-comment'>-- Use readMVar here, not takeMVar,</span>
<a name="line-89"></a> <span class='hs-comment'>-- else dupChan doesn't work</span>
<a name="line-90"></a> <span class='hs-varid'>return</span> <span class='hs-layout'>(</span><span class='hs-varid'>new_read_end</span><span class='hs-layout'>,</span> <span class='hs-varid'>val</span><span class='hs-layout'>)</span>
<a name="line-91"></a>
<a name="line-92"></a><a name="dupChan"></a><span class='hs-comment'>-- |Duplicate a 'Chan': the duplicate channel begins empty, but data written to</span>
<a name="line-93"></a><span class='hs-comment'>-- either channel from then on will be available from both. Hence this creates</span>
<a name="line-94"></a><span class='hs-comment'>-- a kind of broadcast channel, where data written by anyone is seen by</span>
<a name="line-95"></a><span class='hs-comment'>-- everyone else.</span>
<a name="line-96"></a><span class='hs-definition'>dupChan</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Chan</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-layout'>(</span><span class='hs-conid'>Chan</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span>
<a name="line-97"></a><span class='hs-definition'>dupChan</span> <span class='hs-layout'>(</span><span class='hs-conid'>Chan</span> <span class='hs-keyword'>_</span> <span class='hs-varid'>writeVar</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-98"></a> <span class='hs-varid'>hole</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>readMVar</span> <span class='hs-varid'>writeVar</span>
<a name="line-99"></a> <span class='hs-varid'>newReadVar</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>newMVar</span> <span class='hs-varid'>hole</span>
<a name="line-100"></a> <span class='hs-varid'>return</span> <span class='hs-layout'>(</span><span class='hs-conid'>Chan</span> <span class='hs-varid'>newReadVar</span> <span class='hs-varid'>writeVar</span><span class='hs-layout'>)</span>
<a name="line-101"></a>
<a name="line-102"></a><a name="unGetChan"></a><span class='hs-comment'>-- |Put a data item back onto a channel, where it will be the next item read.</span>
<a name="line-103"></a><span class='hs-definition'>unGetChan</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Chan</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-conid'>()</span>
<a name="line-104"></a><span class='hs-definition'>unGetChan</span> <span class='hs-layout'>(</span><span class='hs-conid'>Chan</span> <span class='hs-varid'>readVar</span> <span class='hs-keyword'>_</span><span class='hs-layout'>)</span> <span class='hs-varid'>val</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-105"></a> <span class='hs-varid'>new_read_end</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>newEmptyMVar</span>
<a name="line-106"></a> <span class='hs-varid'>modifyMVar_</span> <span class='hs-varid'>readVar</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>read_end</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyword'>do</span>
<a name="line-107"></a> <span class='hs-varid'>putMVar</span> <span class='hs-varid'>new_read_end</span> <span class='hs-layout'>(</span><span class='hs-conid'>ChItem</span> <span class='hs-varid'>val</span> <span class='hs-varid'>read_end</span><span class='hs-layout'>)</span>
<a name="line-108"></a> <span class='hs-varid'>return</span> <span class='hs-varid'>new_read_end</span>
<a name="line-109"></a><span class='hs-comment'>{-# DEPRECATED unGetChan "if you need this operation, use Control.Concurrent.STM.TChan instead. See <a href="http://hackage.haskell.org/trac/ghc/ticket/4154">http://hackage.haskell.org/trac/ghc/ticket/4154</a> for details" #-}</span>
<a name="line-110"></a>
<a name="line-111"></a><a name="isEmptyChan"></a><span class='hs-comment'>-- |Returns 'True' if the supplied 'Chan' is empty.</span>
<a name="line-112"></a><span class='hs-definition'>isEmptyChan</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Chan</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-conid'>Bool</span>
<a name="line-113"></a><span class='hs-definition'>isEmptyChan</span> <span class='hs-layout'>(</span><span class='hs-conid'>Chan</span> <span class='hs-varid'>readVar</span> <span class='hs-varid'>writeVar</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-114"></a> <span class='hs-varid'>withMVar</span> <span class='hs-varid'>readVar</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>r</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyword'>do</span>
<a name="line-115"></a> <span class='hs-varid'>w</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>readMVar</span> <span class='hs-varid'>writeVar</span>
<a name="line-116"></a> <span class='hs-keyword'>let</span> <span class='hs-varid'>eq</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>r</span> <span class='hs-varop'>==</span> <span class='hs-varid'>w</span>
<a name="line-117"></a> <span class='hs-varid'>eq</span> <span class='hs-varop'>`seq`</span> <span class='hs-varid'>return</span> <span class='hs-varid'>eq</span>
<a name="line-118"></a><span class='hs-comment'>{-# DEPRECATED isEmptyChan "if you need this operation, use Control.Concurrent.STM.TChan instead. See <a href="http://hackage.haskell.org/trac/ghc/ticket/4154">http://hackage.haskell.org/trac/ghc/ticket/4154</a> for details" #-}</span>
<a name="line-119"></a>
<a name="line-120"></a><span class='hs-comment'>-- Operators for interfacing with functional streams.</span>
<a name="line-121"></a>
<a name="line-122"></a><a name="getChanContents"></a><span class='hs-comment'>-- |Return a lazy list representing the contents of the supplied</span>
<a name="line-123"></a><span class='hs-comment'>-- 'Chan', much like 'System.IO.hGetContents'.</span>
<a name="line-124"></a><span class='hs-definition'>getChanContents</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Chan</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-keyglyph'>[</span><span class='hs-varid'>a</span><span class='hs-keyglyph'>]</span>
<a name="line-125"></a><span class='hs-definition'>getChanContents</span> <span class='hs-varid'>ch</span>
<a name="line-126"></a> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>unsafeInterleaveIO</span> <span class='hs-layout'>(</span><span class='hs-keyword'>do</span>
<a name="line-127"></a> <span class='hs-varid'>x</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>readChan</span> <span class='hs-varid'>ch</span>
<a name="line-128"></a> <span class='hs-varid'>xs</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>getChanContents</span> <span class='hs-varid'>ch</span>
<a name="line-129"></a> <span class='hs-varid'>return</span> <span class='hs-layout'>(</span><span class='hs-varid'>x</span><span class='hs-conop'>:</span><span class='hs-varid'>xs</span><span class='hs-layout'>)</span>
<a name="line-130"></a> <span class='hs-layout'>)</span>
<a name="line-131"></a>
<a name="line-132"></a><a name="writeList2Chan"></a><span class='hs-comment'>-- |Write an entire list of items to a 'Chan'.</span>
<a name="line-133"></a><span class='hs-definition'>writeList2Chan</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Chan</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyglyph'>[</span><span class='hs-varid'>a</span><span class='hs-keyglyph'>]</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-conid'>()</span>
<a name="line-134"></a><span class='hs-definition'>writeList2Chan</span> <span class='hs-varid'>ch</span> <span class='hs-varid'>ls</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>sequence_</span> <span class='hs-layout'>(</span><span class='hs-varid'>map</span> <span class='hs-layout'>(</span><span class='hs-varid'>writeChan</span> <span class='hs-varid'>ch</span><span class='hs-layout'>)</span> <span class='hs-varid'>ls</span><span class='hs-layout'>)</span>
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