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<pre><a name="line-1"></a><span class='hs-comment'>{-# OPTIONS_GHC -XNoImplicitPrelude #-}</span>
<a name="line-2"></a><span class='hs-comment'>-----------------------------------------------------------------------------</span>
<a name="line-3"></a><span class='hs-comment'>-- |</span>
<a name="line-4"></a><span class='hs-comment'>-- Module : Control.Concurrent.MVar</span>
<a name="line-5"></a><span class='hs-comment'>-- Copyright : (c) The University of Glasgow 2001</span>
<a name="line-6"></a><span class='hs-comment'>-- License : BSD-style (see the file libraries/base/LICENSE)</span>
<a name="line-7"></a><span class='hs-comment'>-- </span>
<a name="line-8"></a><span class='hs-comment'>-- Maintainer : libraries@haskell.org</span>
<a name="line-9"></a><span class='hs-comment'>-- Stability : experimental</span>
<a name="line-10"></a><span class='hs-comment'>-- Portability : non-portable (concurrency)</span>
<a name="line-11"></a><span class='hs-comment'>--</span>
<a name="line-12"></a><span class='hs-comment'>-- Synchronising variables</span>
<a name="line-13"></a><span class='hs-comment'>--</span>
<a name="line-14"></a><span class='hs-comment'>-----------------------------------------------------------------------------</span>
<a name="line-15"></a>
<a name="line-16"></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'>MVar</span>
<a name="line-17"></a> <span class='hs-layout'>(</span>
<a name="line-18"></a> <span class='hs-comment'>-- * @MVar@s</span>
<a name="line-19"></a> <span class='hs-conid'>MVar</span> <span class='hs-comment'>-- abstract</span>
<a name="line-20"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>newEmptyMVar</span> <span class='hs-comment'>-- :: IO (MVar a)</span>
<a name="line-21"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>newMVar</span> <span class='hs-comment'>-- :: a -> IO (MVar a)</span>
<a name="line-22"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>takeMVar</span> <span class='hs-comment'>-- :: MVar a -> IO a</span>
<a name="line-23"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>putMVar</span> <span class='hs-comment'>-- :: MVar a -> a -> IO ()</span>
<a name="line-24"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>readMVar</span> <span class='hs-comment'>-- :: MVar a -> IO a</span>
<a name="line-25"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>swapMVar</span> <span class='hs-comment'>-- :: MVar a -> a -> IO a</span>
<a name="line-26"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>tryTakeMVar</span> <span class='hs-comment'>-- :: MVar a -> IO (Maybe a)</span>
<a name="line-27"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>tryPutMVar</span> <span class='hs-comment'>-- :: MVar a -> a -> IO Bool</span>
<a name="line-28"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>isEmptyMVar</span> <span class='hs-comment'>-- :: MVar a -> IO Bool</span>
<a name="line-29"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>withMVar</span> <span class='hs-comment'>-- :: MVar a -> (a -> IO b) -> IO b</span>
<a name="line-30"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>modifyMVar_</span> <span class='hs-comment'>-- :: MVar a -> (a -> IO a) -> IO ()</span>
<a name="line-31"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>modifyMVar</span> <span class='hs-comment'>-- :: MVar a -> (a -> IO (a,b)) -> IO b</span>
<a name="line-32"></a><span class='hs-cpp'>#ifndef __HUGS__</span>
<a name="line-33"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>addMVarFinalizer</span> <span class='hs-comment'>-- :: MVar a -> IO () -> IO ()</span>
<a name="line-34"></a><span class='hs-cpp'>#endif</span>
<a name="line-35"></a> <span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-36"></a>
<a name="line-37"></a><span class='hs-cpp'>#ifdef __HUGS__</span>
<a name="line-38"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Hugs</span><span class='hs-varop'>.</span><span class='hs-conid'>ConcBase</span> <span class='hs-layout'>(</span> <span class='hs-conid'>MVar</span><span class='hs-layout'>,</span> <span class='hs-varid'>newEmptyMVar</span><span class='hs-layout'>,</span> <span class='hs-varid'>newMVar</span><span class='hs-layout'>,</span> <span class='hs-varid'>takeMVar</span><span class='hs-layout'>,</span> <span class='hs-varid'>putMVar</span><span class='hs-layout'>,</span>
<a name="line-39"></a> <span class='hs-varid'>tryTakeMVar</span><span class='hs-layout'>,</span> <span class='hs-varid'>tryPutMVar</span><span class='hs-layout'>,</span> <span class='hs-varid'>isEmptyMVar</span><span class='hs-layout'>,</span>
<a name="line-40"></a> <span class='hs-layout'>)</span>
<a name="line-41"></a><span class='hs-cpp'>#endif</span>
<a name="line-42"></a>
<a name="line-43"></a><span class='hs-cpp'>#ifdef __GLASGOW_HASKELL__</span>
<a name="line-44"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>GHC</span><span class='hs-varop'>.</span><span class='hs-conid'>MVar</span> <span class='hs-layout'>(</span> <span class='hs-conid'>MVar</span><span class='hs-layout'>,</span> <span class='hs-varid'>newEmptyMVar</span><span class='hs-layout'>,</span> <span class='hs-varid'>newMVar</span><span class='hs-layout'>,</span> <span class='hs-varid'>takeMVar</span><span class='hs-layout'>,</span> <span class='hs-varid'>putMVar</span><span class='hs-layout'>,</span>
<a name="line-45"></a> <span class='hs-varid'>tryTakeMVar</span><span class='hs-layout'>,</span> <span class='hs-varid'>tryPutMVar</span><span class='hs-layout'>,</span> <span class='hs-varid'>isEmptyMVar</span><span class='hs-layout'>,</span> <span class='hs-varid'>addMVarFinalizer</span>
<a name="line-46"></a> <span class='hs-layout'>)</span>
<a name="line-47"></a><span class='hs-cpp'>#endif</span>
<a name="line-48"></a>
<a name="line-49"></a><span class='hs-cpp'>#ifdef __GLASGOW_HASKELL__</span>
<a name="line-50"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>GHC</span><span class='hs-varop'>.</span><span class='hs-conid'>Base</span>
<a name="line-51"></a><span class='hs-cpp'>#else</span>
<a name="line-52"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Prelude</span>
<a name="line-53"></a><span class='hs-cpp'>#endif</span>
<a name="line-54"></a>
<a name="line-55"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Exception</span><span class='hs-varop'>.</span><span class='hs-conid'>Base</span>
<a name="line-56"></a>
<a name="line-57"></a><a name="readMVar"></a><span class='hs-comment'>{-|
<a name="line-58"></a> This is a combination of 'takeMVar' and 'putMVar'; ie. it takes the value
<a name="line-59"></a> from the 'MVar', puts it back, and also returns it.
<a name="line-60"></a>-}</span>
<a name="line-61"></a><span class='hs-definition'>readMVar</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>MVar</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-62"></a><span class='hs-definition'>readMVar</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=</span>
<a name="line-63"></a> <span class='hs-varid'>mask_</span> <span class='hs-varop'>$</span> <span class='hs-keyword'>do</span>
<a name="line-64"></a> <span class='hs-varid'>a</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>takeMVar</span> <span class='hs-varid'>m</span>
<a name="line-65"></a> <span class='hs-varid'>putMVar</span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span>
<a name="line-66"></a> <span class='hs-varid'>return</span> <span class='hs-varid'>a</span>
<a name="line-67"></a>
<a name="line-68"></a><a name="swapMVar"></a><span class='hs-comment'>{-|
<a name="line-69"></a> Take a value from an 'MVar', put a new value into the 'MVar' and
<a name="line-70"></a> return the value taken. Note that there is a race condition whereby
<a name="line-71"></a> another process can put something in the 'MVar' after the take
<a name="line-72"></a> happens but before the put does.
<a name="line-73"></a>-}</span>
<a name="line-74"></a><span class='hs-definition'>swapMVar</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>MVar</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-varid'>a</span>
<a name="line-75"></a><span class='hs-definition'>swapMVar</span> <span class='hs-varid'>mvar</span> <span class='hs-varid'>new</span> <span class='hs-keyglyph'>=</span>
<a name="line-76"></a> <span class='hs-varid'>mask_</span> <span class='hs-varop'>$</span> <span class='hs-keyword'>do</span>
<a name="line-77"></a> <span class='hs-varid'>old</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>takeMVar</span> <span class='hs-varid'>mvar</span>
<a name="line-78"></a> <span class='hs-varid'>putMVar</span> <span class='hs-varid'>mvar</span> <span class='hs-varid'>new</span>
<a name="line-79"></a> <span class='hs-varid'>return</span> <span class='hs-varid'>old</span>
<a name="line-80"></a>
<a name="line-81"></a><a name="withMVar"></a><span class='hs-comment'>{-|
<a name="line-82"></a> 'withMVar' is a safe wrapper for operating on the contents of an
<a name="line-83"></a> 'MVar'. This operation is exception-safe: it will replace the
<a name="line-84"></a> original contents of the 'MVar' if an exception is raised (see
<a name="line-85"></a> "Control.Exception").
<a name="line-86"></a>-}</span>
<a name="line-87"></a><span class='hs-comment'>{-# INLINE withMVar #-}</span>
<a name="line-88"></a><span class='hs-comment'>-- inlining has been reported to have dramatic effects; see</span>
<a name="line-89"></a><span class='hs-comment'>-- <a href="http://www.haskell.org//pipermail/haskell/2006-May/017907.html">http://www.haskell.org//pipermail/haskell/2006-May/017907.html</a></span>
<a name="line-90"></a><span class='hs-definition'>withMVar</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>MVar</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-varid'>b</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-varid'>b</span>
<a name="line-91"></a><span class='hs-definition'>withMVar</span> <span class='hs-varid'>m</span> <span class='hs-varid'>io</span> <span class='hs-keyglyph'>=</span>
<a name="line-92"></a> <span class='hs-varid'>mask</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>restore</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyword'>do</span>
<a name="line-93"></a> <span class='hs-varid'>a</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>takeMVar</span> <span class='hs-varid'>m</span>
<a name="line-94"></a> <span class='hs-varid'>b</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>restore</span> <span class='hs-layout'>(</span><span class='hs-varid'>io</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-varop'>`onException`</span> <span class='hs-varid'>putMVar</span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span>
<a name="line-95"></a> <span class='hs-varid'>putMVar</span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span>
<a name="line-96"></a> <span class='hs-varid'>return</span> <span class='hs-varid'>b</span>
<a name="line-97"></a>
<a name="line-98"></a><a name="modifyMVar_"></a><span class='hs-comment'>{-|
<a name="line-99"></a> A safe wrapper for modifying the contents of an 'MVar'. Like 'withMVar',
<a name="line-100"></a> 'modifyMVar' will replace the original contents of the 'MVar' if an
<a name="line-101"></a> exception is raised during the operation.
<a name="line-102"></a>-}</span>
<a name="line-103"></a><span class='hs-comment'>{-# INLINE modifyMVar_ #-}</span>
<a name="line-104"></a><span class='hs-definition'>modifyMVar_</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>MVar</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-conid'>()</span>
<a name="line-105"></a><span class='hs-definition'>modifyMVar_</span> <span class='hs-varid'>m</span> <span class='hs-varid'>io</span> <span class='hs-keyglyph'>=</span>
<a name="line-106"></a> <span class='hs-varid'>mask</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>restore</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyword'>do</span>
<a name="line-107"></a> <span class='hs-varid'>a</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>takeMVar</span> <span class='hs-varid'>m</span>
<a name="line-108"></a> <span class='hs-varid'>a'</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>restore</span> <span class='hs-layout'>(</span><span class='hs-varid'>io</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-varop'>`onException`</span> <span class='hs-varid'>putMVar</span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span>
<a name="line-109"></a> <span class='hs-varid'>putMVar</span> <span class='hs-varid'>m</span> <span class='hs-varid'>a'</span>
<a name="line-110"></a>
<a name="line-111"></a><a name="modifyMVar"></a><span class='hs-comment'>{-|
<a name="line-112"></a> A slight variation on 'modifyMVar_' that allows a value to be
<a name="line-113"></a> returned (@b@) in addition to the modified value of the 'MVar'.
<a name="line-114"></a>-}</span>
<a name="line-115"></a><span class='hs-comment'>{-# INLINE modifyMVar #-}</span>
<a name="line-116"></a><span class='hs-definition'>modifyMVar</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>MVar</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</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-varid'>a</span><span class='hs-layout'>,</span><span class='hs-varid'>b</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-varid'>b</span>
<a name="line-117"></a><span class='hs-definition'>modifyMVar</span> <span class='hs-varid'>m</span> <span class='hs-varid'>io</span> <span class='hs-keyglyph'>=</span>
<a name="line-118"></a> <span class='hs-varid'>mask</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>restore</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyword'>do</span>
<a name="line-119"></a> <span class='hs-varid'>a</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>takeMVar</span> <span class='hs-varid'>m</span>
<a name="line-120"></a> <span class='hs-layout'>(</span><span class='hs-varid'>a'</span><span class='hs-layout'>,</span><span class='hs-varid'>b</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>restore</span> <span class='hs-layout'>(</span><span class='hs-varid'>io</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-varop'>`onException`</span> <span class='hs-varid'>putMVar</span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span>
<a name="line-121"></a> <span class='hs-varid'>putMVar</span> <span class='hs-varid'>m</span> <span class='hs-varid'>a'</span>
<a name="line-122"></a> <span class='hs-varid'>return</span> <span class='hs-varid'>b</span>
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