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<pre><a name="line-1"></a><span class='hs-comment'>{-# OPTIONS_GHC -XNoImplicitPrelude -funbox-strict-fields #-}</span>
<a name="line-2"></a><span class='hs-comment'>{-# OPTIONS_HADDOCK hide #-}</span>
<a name="line-3"></a><span class='hs-comment'>-----------------------------------------------------------------------------</span>
<a name="line-4"></a><span class='hs-comment'>-- |</span>
<a name="line-5"></a><span class='hs-comment'>-- Module : GHC.MVar</span>
<a name="line-6"></a><span class='hs-comment'>-- Copyright : (c) The University of Glasgow 2008</span>
<a name="line-7"></a><span class='hs-comment'>-- License : see libraries/base/LICENSE</span>
<a name="line-8"></a><span class='hs-comment'>-- </span>
<a name="line-9"></a><span class='hs-comment'>-- Maintainer : cvs-ghc@haskell.org</span>
<a name="line-10"></a><span class='hs-comment'>-- Stability : internal</span>
<a name="line-11"></a><span class='hs-comment'>-- Portability : non-portable (GHC Extensions)</span>
<a name="line-12"></a><span class='hs-comment'>--</span>
<a name="line-13"></a><span class='hs-comment'>-- The MVar type</span>
<a name="line-14"></a><span class='hs-comment'>--</span>
<a name="line-15"></a><span class='hs-comment'>-----------------------------------------------------------------------------</span>
<a name="line-16"></a>
<a name="line-17"></a><span class='hs-keyword'>module</span> <span class='hs-conid'>GHC</span><span class='hs-varop'>.</span><span class='hs-conid'>MVar</span> <span class='hs-layout'>(</span>
<a name="line-18"></a> <span class='hs-comment'>-- * MVars</span>
<a name="line-19"></a> <span class='hs-conid'>MVar</span><span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span>
<a name="line-20"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>newMVar</span> <span class='hs-comment'>-- :: a -> IO (MVar a)</span>
<a name="line-21"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>newEmptyMVar</span> <span class='hs-comment'>-- :: 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'>tryTakeMVar</span> <span class='hs-comment'>-- :: MVar a -> IO (Maybe a)</span>
<a name="line-25"></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-26"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>isEmptyMVar</span> <span class='hs-comment'>-- :: MVar a -> IO Bool</span>
<a name="line-27"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>addMVarFinalizer</span> <span class='hs-comment'>-- :: MVar a -> IO () -> IO ()</span>
<a name="line-28"></a>
<a name="line-29"></a> <span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-30"></a>
<a name="line-31"></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-32"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>GHC</span><span class='hs-varop'>.</span><span class='hs-conid'>IO</span><span class='hs-conid'>()</span> <span class='hs-comment'>-- instance Monad IO</span>
<a name="line-33"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Maybe</span>
<a name="line-34"></a>
<a name="line-35"></a><a name="MVar"></a><span class='hs-keyword'>data</span> <span class='hs-conid'>MVar</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'>MVar</span><span class='hs-cpp'>#</span> <span class='hs-conid'>RealWorld</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span>
<a name="line-36"></a><span class='hs-comment'>{- ^
<a name="line-37"></a>An 'MVar' (pronounced \"em-var\") is a synchronising variable, used
<a name="line-38"></a>for communication between concurrent threads. It can be thought of
<a name="line-39"></a>as a a box, which may be empty or full.
<a name="line-40"></a>-}</span>
<a name="line-41"></a>
<a name="line-42"></a><span class='hs-comment'>-- pull in Eq (Mvar a) too, to avoid GHC.Conc being an orphan-instance module</span>
<a name="line-43"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Eq</span> <span class='hs-layout'>(</span><span class='hs-conid'>MVar</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-44"></a> <span class='hs-layout'>(</span><span class='hs-conid'>MVar</span> <span class='hs-varid'>mvar1</span><span class='hs-cpp'>#</span><span class='hs-layout'>)</span> <span class='hs-varop'>==</span> <span class='hs-layout'>(</span><span class='hs-conid'>MVar</span> <span class='hs-varid'>mvar2</span><span class='hs-cpp'>#</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>sameMVar</span><span class='hs-cpp'>#</span> <span class='hs-varid'>mvar1</span><span class='hs-cpp'>#</span> <span class='hs-varid'>mvar2</span><span class='hs-cpp'>#</span>
<a name="line-45"></a>
<a name="line-46"></a><span class='hs-comment'>{-
<a name="line-47"></a>M-Vars are rendezvous points for concurrent threads. They begin
<a name="line-48"></a>empty, and any attempt to read an empty M-Var blocks. When an M-Var
<a name="line-49"></a>is written, a single blocked thread may be freed. Reading an M-Var
<a name="line-50"></a>toggles its state from full back to empty. Therefore, any value
<a name="line-51"></a>written to an M-Var may only be read once. Multiple reads and writes
<a name="line-52"></a>are allowed, but there must be at least one read between any two
<a name="line-53"></a>writes.
<a name="line-54"></a>-}</span>
<a name="line-55"></a>
<a name="line-56"></a><span class='hs-comment'>--Defined in IOBase to avoid cycle: data MVar a = MVar (SynchVar# RealWorld a)</span>
<a name="line-57"></a>
<a name="line-58"></a><a name="newEmptyMVar"></a><span class='hs-comment'>-- |Create an 'MVar' which is initially empty.</span>
<a name="line-59"></a><span class='hs-definition'>newEmptyMVar</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>IO</span> <span class='hs-layout'>(</span><span class='hs-conid'>MVar</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span>
<a name="line-60"></a><span class='hs-definition'>newEmptyMVar</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>IO</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span> <span class='hs-varid'>s</span><span class='hs-cpp'>#</span> <span class='hs-keyglyph'>-></span>
<a name="line-61"></a> <span class='hs-keyword'>case</span> <span class='hs-varid'>newMVar</span><span class='hs-cpp'>#</span> <span class='hs-varid'>s</span><span class='hs-cpp'>#</span> <span class='hs-keyword'>of</span>
<a name="line-62"></a> <span class='hs-layout'>(</span><span class='hs-cpp'>#</span> <span class='hs-varid'>s2</span><span class='hs-cpp'>#</span><span class='hs-layout'>,</span> <span class='hs-varid'>svar</span><span class='hs-cpp'>#</span> <span class='hs-cpp'>#</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-cpp'>#</span> <span class='hs-varid'>s2</span><span class='hs-cpp'>#</span><span class='hs-layout'>,</span> <span class='hs-conid'>MVar</span> <span class='hs-varid'>svar</span><span class='hs-cpp'>#</span> <span class='hs-cpp'>#</span><span class='hs-layout'>)</span>
<a name="line-63"></a>
<a name="line-64"></a><a name="newMVar"></a><span class='hs-comment'>-- |Create an 'MVar' which contains the supplied value.</span>
<a name="line-65"></a><span class='hs-definition'>newMVar</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-layout'>(</span><span class='hs-conid'>MVar</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span>
<a name="line-66"></a><span class='hs-definition'>newMVar</span> <span class='hs-varid'>value</span> <span class='hs-keyglyph'>=</span>
<a name="line-67"></a> <span class='hs-varid'>newEmptyMVar</span> <span class='hs-varop'>>>=</span> <span class='hs-keyglyph'>\</span> <span class='hs-varid'>mvar</span> <span class='hs-keyglyph'>-></span>
<a name="line-68"></a> <span class='hs-varid'>putMVar</span> <span class='hs-varid'>mvar</span> <span class='hs-varid'>value</span> <span class='hs-varop'>>></span>
<a name="line-69"></a> <span class='hs-varid'>return</span> <span class='hs-varid'>mvar</span>
<a name="line-70"></a>
<a name="line-71"></a><a name="takeMVar"></a><span class='hs-comment'>-- |Return the contents of the 'MVar'. If the 'MVar' is currently</span>
<a name="line-72"></a><span class='hs-comment'>-- empty, 'takeMVar' will wait until it is full. After a 'takeMVar', </span>
<a name="line-73"></a><span class='hs-comment'>-- the 'MVar' is left empty.</span>
<a name="line-74"></a><span class='hs-comment'>-- </span>
<a name="line-75"></a><span class='hs-comment'>-- There are two further important properties of 'takeMVar':</span>
<a name="line-76"></a><span class='hs-comment'>--</span>
<a name="line-77"></a><span class='hs-comment'>-- * 'takeMVar' is single-wakeup. That is, if there are multiple</span>
<a name="line-78"></a><span class='hs-comment'>-- threads blocked in 'takeMVar', and the 'MVar' becomes full,</span>
<a name="line-79"></a><span class='hs-comment'>-- only one thread will be woken up. The runtime guarantees that</span>
<a name="line-80"></a><span class='hs-comment'>-- the woken thread completes its 'takeMVar' operation.</span>
<a name="line-81"></a><span class='hs-comment'>--</span>
<a name="line-82"></a><span class='hs-comment'>-- * When multiple threads are blocked on an 'MVar', they are</span>
<a name="line-83"></a><span class='hs-comment'>-- woken up in FIFO order. This is useful for providing</span>
<a name="line-84"></a><span class='hs-comment'>-- fairness properties of abstractions built using 'MVar's.</span>
<a name="line-85"></a><span class='hs-comment'>--</span>
<a name="line-86"></a><span class='hs-definition'>takeMVar</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-87"></a><span class='hs-definition'>takeMVar</span> <span class='hs-layout'>(</span><span class='hs-conid'>MVar</span> <span class='hs-varid'>mvar</span><span class='hs-cpp'>#</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>IO</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span> <span class='hs-varid'>s</span><span class='hs-cpp'>#</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>takeMVar</span><span class='hs-cpp'>#</span> <span class='hs-varid'>mvar</span><span class='hs-cpp'>#</span> <span class='hs-varid'>s</span><span class='hs-cpp'>#</span>
<a name="line-88"></a>
<a name="line-89"></a><a name="putMVar"></a><span class='hs-comment'>-- |Put a value into an 'MVar'. If the 'MVar' is currently full,</span>
<a name="line-90"></a><span class='hs-comment'>-- 'putMVar' will wait until it becomes empty.</span>
<a name="line-91"></a><span class='hs-comment'>--</span>
<a name="line-92"></a><span class='hs-comment'>-- There are two further important properties of 'putMVar':</span>
<a name="line-93"></a><span class='hs-comment'>--</span>
<a name="line-94"></a><span class='hs-comment'>-- * 'putMVar' is single-wakeup. That is, if there are multiple</span>
<a name="line-95"></a><span class='hs-comment'>-- threads blocked in 'putMVar', and the 'MVar' becomes empty,</span>
<a name="line-96"></a><span class='hs-comment'>-- only one thread will be woken up. The runtime guarantees that</span>
<a name="line-97"></a><span class='hs-comment'>-- the woken thread completes its 'putMVar' operation.</span>
<a name="line-98"></a><span class='hs-comment'>--</span>
<a name="line-99"></a><span class='hs-comment'>-- * When multiple threads are blocked on an 'MVar', they are</span>
<a name="line-100"></a><span class='hs-comment'>-- woken up in FIFO order. This is useful for providing</span>
<a name="line-101"></a><span class='hs-comment'>-- fairness properties of abstractions built using 'MVar's.</span>
<a name="line-102"></a><span class='hs-comment'>--</span>
<a name="line-103"></a><span class='hs-definition'>putMVar</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-conid'>()</span>
<a name="line-104"></a><span class='hs-definition'>putMVar</span> <span class='hs-layout'>(</span><span class='hs-conid'>MVar</span> <span class='hs-varid'>mvar</span><span class='hs-cpp'>#</span><span class='hs-layout'>)</span> <span class='hs-varid'>x</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>IO</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span> <span class='hs-varid'>s</span><span class='hs-cpp'>#</span> <span class='hs-keyglyph'>-></span>
<a name="line-105"></a> <span class='hs-keyword'>case</span> <span class='hs-varid'>putMVar</span><span class='hs-cpp'>#</span> <span class='hs-varid'>mvar</span><span class='hs-cpp'>#</span> <span class='hs-varid'>x</span> <span class='hs-varid'>s</span><span class='hs-cpp'>#</span> <span class='hs-keyword'>of</span>
<a name="line-106"></a> <span class='hs-varid'>s2</span><span class='hs-cpp'>#</span> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-cpp'>#</span> <span class='hs-varid'>s2</span><span class='hs-cpp'>#</span><span class='hs-layout'>,</span> <span class='hs-conid'>()</span> <span class='hs-cpp'>#</span><span class='hs-layout'>)</span>
<a name="line-107"></a>
<a name="line-108"></a><a name="tryTakeMVar"></a><span class='hs-comment'>-- |A non-blocking version of 'takeMVar'. The 'tryTakeMVar' function</span>
<a name="line-109"></a><span class='hs-comment'>-- returns immediately, with 'Nothing' if the 'MVar' was empty, or</span>
<a name="line-110"></a><span class='hs-comment'>-- @'Just' a@ if the 'MVar' was full with contents @a@. After 'tryTakeMVar',</span>
<a name="line-111"></a><span class='hs-comment'>-- the 'MVar' is left empty.</span>
<a name="line-112"></a><span class='hs-definition'>tryTakeMVar</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-layout'>(</span><span class='hs-conid'>Maybe</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span>
<a name="line-113"></a><span class='hs-definition'>tryTakeMVar</span> <span class='hs-layout'>(</span><span class='hs-conid'>MVar</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>IO</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span> <span class='hs-varid'>s</span> <span class='hs-keyglyph'>-></span>
<a name="line-114"></a> <span class='hs-keyword'>case</span> <span class='hs-varid'>tryTakeMVar</span><span class='hs-cpp'>#</span> <span class='hs-varid'>m</span> <span class='hs-varid'>s</span> <span class='hs-keyword'>of</span>
<a name="line-115"></a> <span class='hs-layout'>(</span><span class='hs-cpp'>#</span> <span class='hs-varid'>s'</span><span class='hs-layout'>,</span> <span class='hs-num'>0</span><span class='hs-cpp'>#</span><span class='hs-layout'>,</span> <span class='hs-keyword'>_</span> <span class='hs-cpp'>#</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-cpp'>#</span> <span class='hs-varid'>s'</span><span class='hs-layout'>,</span> <span class='hs-conid'>Nothing</span> <span class='hs-cpp'>#</span><span class='hs-layout'>)</span> <span class='hs-comment'>-- MVar is empty</span>
<a name="line-116"></a> <span class='hs-layout'>(</span><span class='hs-cpp'>#</span> <span class='hs-varid'>s'</span><span class='hs-layout'>,</span> <span class='hs-keyword'>_</span><span class='hs-layout'>,</span> <span class='hs-varid'>a</span> <span class='hs-cpp'>#</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-cpp'>#</span> <span class='hs-varid'>s'</span><span class='hs-layout'>,</span> <span class='hs-conid'>Just</span> <span class='hs-varid'>a</span> <span class='hs-cpp'>#</span><span class='hs-layout'>)</span> <span class='hs-comment'>-- MVar is full</span>
<a name="line-117"></a>
<a name="line-118"></a><a name="tryPutMVar"></a><span class='hs-comment'>-- |A non-blocking version of 'putMVar'. The 'tryPutMVar' function</span>
<a name="line-119"></a><span class='hs-comment'>-- attempts to put the value @a@ into the 'MVar', returning 'True' if</span>
<a name="line-120"></a><span class='hs-comment'>-- it was successful, or 'False' otherwise.</span>
<a name="line-121"></a><span class='hs-definition'>tryPutMVar</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-conid'>Bool</span>
<a name="line-122"></a><span class='hs-definition'>tryPutMVar</span> <span class='hs-layout'>(</span><span class='hs-conid'>MVar</span> <span class='hs-varid'>mvar</span><span class='hs-cpp'>#</span><span class='hs-layout'>)</span> <span class='hs-varid'>x</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>IO</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span> <span class='hs-varid'>s</span><span class='hs-cpp'>#</span> <span class='hs-keyglyph'>-></span>
<a name="line-123"></a> <span class='hs-keyword'>case</span> <span class='hs-varid'>tryPutMVar</span><span class='hs-cpp'>#</span> <span class='hs-varid'>mvar</span><span class='hs-cpp'>#</span> <span class='hs-varid'>x</span> <span class='hs-varid'>s</span><span class='hs-cpp'>#</span> <span class='hs-keyword'>of</span>
<a name="line-124"></a> <span class='hs-layout'>(</span><span class='hs-cpp'>#</span> <span class='hs-varid'>s</span><span class='hs-layout'>,</span> <span class='hs-num'>0</span><span class='hs-cpp'>#</span> <span class='hs-cpp'>#</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-cpp'>#</span> <span class='hs-varid'>s</span><span class='hs-layout'>,</span> <span class='hs-conid'>False</span> <span class='hs-cpp'>#</span><span class='hs-layout'>)</span>
<a name="line-125"></a> <span class='hs-layout'>(</span><span class='hs-cpp'>#</span> <span class='hs-varid'>s</span><span class='hs-layout'>,</span> <span class='hs-keyword'>_</span> <span class='hs-cpp'>#</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-cpp'>#</span> <span class='hs-varid'>s</span><span class='hs-layout'>,</span> <span class='hs-conid'>True</span> <span class='hs-cpp'>#</span><span class='hs-layout'>)</span>
<a name="line-126"></a>
<a name="line-127"></a><a name="isEmptyMVar"></a><span class='hs-comment'>-- |Check whether a given 'MVar' is empty.</span>
<a name="line-128"></a><span class='hs-comment'>--</span>
<a name="line-129"></a><span class='hs-comment'>-- Notice that the boolean value returned is just a snapshot of</span>
<a name="line-130"></a><span class='hs-comment'>-- the state of the MVar. By the time you get to react on its result,</span>
<a name="line-131"></a><span class='hs-comment'>-- the MVar may have been filled (or emptied) - so be extremely</span>
<a name="line-132"></a><span class='hs-comment'>-- careful when using this operation. Use 'tryTakeMVar' instead if possible.</span>
<a name="line-133"></a><span class='hs-definition'>isEmptyMVar</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-conid'>Bool</span>
<a name="line-134"></a><span class='hs-definition'>isEmptyMVar</span> <span class='hs-layout'>(</span><span class='hs-conid'>MVar</span> <span class='hs-varid'>mv</span><span class='hs-cpp'>#</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>IO</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span> <span class='hs-varid'>s</span><span class='hs-cpp'>#</span> <span class='hs-keyglyph'>-></span>
<a name="line-135"></a> <span class='hs-keyword'>case</span> <span class='hs-varid'>isEmptyMVar</span><span class='hs-cpp'>#</span> <span class='hs-varid'>mv</span><span class='hs-cpp'>#</span> <span class='hs-varid'>s</span><span class='hs-cpp'>#</span> <span class='hs-keyword'>of</span>
<a name="line-136"></a> <span class='hs-layout'>(</span><span class='hs-cpp'>#</span> <span class='hs-varid'>s2</span><span class='hs-cpp'>#</span><span class='hs-layout'>,</span> <span class='hs-varid'>flg</span> <span class='hs-cpp'>#</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-cpp'>#</span> <span class='hs-varid'>s2</span><span class='hs-cpp'>#</span><span class='hs-layout'>,</span> <span class='hs-varid'>not</span> <span class='hs-layout'>(</span><span class='hs-varid'>flg</span> <span class='hs-varop'>==#</span> <span class='hs-num'>0</span><span class='hs-cpp'>#</span><span class='hs-layout'>)</span> <span class='hs-cpp'>#</span><span class='hs-layout'>)</span>
<a name="line-137"></a>
<a name="line-138"></a><a name="addMVarFinalizer"></a><span class='hs-comment'>-- |Add a finalizer to an 'MVar' (GHC only). See "Foreign.ForeignPtr" and</span>
<a name="line-139"></a><span class='hs-comment'>-- "System.Mem.Weak" for more about finalizers.</span>
<a name="line-140"></a><span class='hs-definition'>addMVarFinalizer</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-conid'>()</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-conid'>()</span>
<a name="line-141"></a><span class='hs-definition'>addMVarFinalizer</span> <span class='hs-layout'>(</span><span class='hs-conid'>MVar</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-varid'>finalizer</span> <span class='hs-keyglyph'>=</span>
<a name="line-142"></a> <span class='hs-conid'>IO</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>s</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyword'>case</span> <span class='hs-varid'>mkWeak</span><span class='hs-cpp'>#</span> <span class='hs-varid'>m</span> <span class='hs-conid'>()</span> <span class='hs-varid'>finalizer</span> <span class='hs-varid'>s</span> <span class='hs-keyword'>of</span> <span class='hs-layout'>{</span> <span class='hs-layout'>(</span><span class='hs-cpp'>#</span> <span class='hs-varid'>s1</span><span class='hs-layout'>,</span> <span class='hs-keyword'>_</span> <span class='hs-cpp'>#</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-cpp'>#</span> <span class='hs-varid'>s1</span><span class='hs-layout'>,</span> <span class='hs-conid'>()</span> <span class='hs-cpp'>#</span><span class='hs-layout'>)</span> <span class='hs-layout'>}</span>
<a name="line-143"></a>
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