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<title>src/Control/Concurrent/STM/TBMChan.hs</title>
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<pre><a name="line-1"></a><span class='hs-comment'>{-# OPTIONS_GHC -Wall -fwarn-tabs #-}</span>
<a name="line-2"></a><span class='hs-comment'>{-# LANGUAGE CPP, DeriveDataTypeable #-}</span>
<a name="line-3"></a>
<a name="line-4"></a><span class='hs-comment'>-- HACK: in GHC 7.10, Haddock complains about Control.Monad.STM and</span>
<a name="line-5"></a><span class='hs-comment'>-- System.IO.Unsafe being imported but unused. However, if we use</span>
<a name="line-6"></a><span class='hs-comment'>-- CPP to avoid including them under Haddock, then it will fail to</span>
<a name="line-7"></a><span class='hs-comment'>-- compile!</span>
<a name="line-8"></a><span class='hs-cpp'>#ifdef __HADDOCK__</span>
<a name="line-9"></a><span class='hs-comment'>{-# OPTIONS_GHC -fno-warn-unused-imports #-}</span>
<a name="line-10"></a><span class='hs-cpp'>#endif</span>
<a name="line-11"></a>
<a name="line-12"></a><span class='hs-cpp'>#if __GLASGOW_HASKELL__ >= 701</span>
<a name="line-13"></a><span class='hs-cpp'># ifdef __HADDOCK__</span>
<a name="line-14"></a><span class='hs-comment'>{-# LANGUAGE Trustworthy #-}</span>
<a name="line-15"></a><span class='hs-cpp'># else</span>
<a name="line-16"></a><span class='hs-comment'>{-# LANGUAGE Safe #-}</span>
<a name="line-17"></a><span class='hs-cpp'># endif</span>
<a name="line-18"></a><span class='hs-cpp'>#endif</span>
<a name="line-19"></a><span class='hs-comment'>----------------------------------------------------------------</span>
<a name="line-20"></a><span class='hs-comment'>-- 2015.03.29</span>
<a name="line-21"></a><span class='hs-comment'>-- |</span>
<a name="line-22"></a><span class='hs-comment'>-- Module : Control.Concurrent.STM.TBMChan</span>
<a name="line-23"></a><span class='hs-comment'>-- Copyright : Copyright (c) 2011--2015 wren gayle romano</span>
<a name="line-24"></a><span class='hs-comment'>-- License : BSD</span>
<a name="line-25"></a><span class='hs-comment'>-- Maintainer : wren@community.haskell.org</span>
<a name="line-26"></a><span class='hs-comment'>-- Stability : provisional</span>
<a name="line-27"></a><span class='hs-comment'>-- Portability : non-portable (GHC STM, DeriveDataTypeable)</span>
<a name="line-28"></a><span class='hs-comment'>--</span>
<a name="line-29"></a><span class='hs-comment'>-- A version of "Control.Concurrent.STM.TChan" where the queue is</span>
<a name="line-30"></a><span class='hs-comment'>-- bounded in length and closeable. This combines the abilities of</span>
<a name="line-31"></a><span class='hs-comment'>-- "Control.Concurrent.STM.TBChan" and "Control.Concurrent.STM.TMChan".</span>
<a name="line-32"></a><span class='hs-comment'>-- This variant incorporates ideas from Thomas M. DuBuisson's</span>
<a name="line-33"></a><span class='hs-comment'>-- @bounded-tchan@ package in order to reduce contention between</span>
<a name="line-34"></a><span class='hs-comment'>-- readers and writers.</span>
<a name="line-35"></a><span class='hs-comment'>----------------------------------------------------------------</span>
<a name="line-36"></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'>STM</span><span class='hs-varop'>.</span><span class='hs-conid'>TBMChan</span>
<a name="line-37"></a> <span class='hs-layout'>(</span>
<a name="line-38"></a> <span class='hs-comment'>-- * The TBMChan type</span>
<a name="line-39"></a> <span class='hs-conid'>TBMChan</span><span class='hs-conid'>()</span>
<a name="line-40"></a> <span class='hs-comment'>-- ** Creating TBMChans</span>
<a name="line-41"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>newTBMChan</span>
<a name="line-42"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>newTBMChanIO</span>
<a name="line-43"></a> <span class='hs-comment'>-- I don't know how to define dupTBMChan with the correct semantics</span>
<a name="line-44"></a> <span class='hs-comment'>-- ** Reading from TBMChans</span>
<a name="line-45"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>readTBMChan</span>
<a name="line-46"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>tryReadTBMChan</span>
<a name="line-47"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>peekTBMChan</span>
<a name="line-48"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>tryPeekTBMChan</span>
<a name="line-49"></a> <span class='hs-comment'>-- ** Writing to TBMChans</span>
<a name="line-50"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>writeTBMChan</span>
<a name="line-51"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>tryWriteTBMChan</span>
<a name="line-52"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>unGetTBMChan</span>
<a name="line-53"></a> <span class='hs-comment'>-- ** Closing TBMChans</span>
<a name="line-54"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>closeTBMChan</span>
<a name="line-55"></a> <span class='hs-comment'>-- ** Predicates</span>
<a name="line-56"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>isClosedTBMChan</span>
<a name="line-57"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>isEmptyTBMChan</span>
<a name="line-58"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>isFullTBMChan</span>
<a name="line-59"></a> <span class='hs-comment'>-- ** Other functionality</span>
<a name="line-60"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>estimateFreeSlotsTBMChan</span>
<a name="line-61"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>freeSlotsTBMChan</span>
<a name="line-62"></a> <span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-63"></a>
<a name="line-64"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Prelude</span> <span class='hs-varid'>hiding</span> <span class='hs-layout'>(</span><span class='hs-varid'>reads</span><span class='hs-layout'>)</span>
<a name="line-65"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Typeable</span> <span class='hs-layout'>(</span><span class='hs-conid'>Typeable</span><span class='hs-layout'>)</span>
<a name="line-66"></a><span class='hs-cpp'>#if __GLASGOW_HASKELL__ < 710</span>
<a name="line-67"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Applicative</span> <span class='hs-layout'>(</span><span class='hs-layout'>(</span><span class='hs-varop'><$></span><span class='hs-layout'>)</span><span class='hs-layout'>)</span>
<a name="line-68"></a><span class='hs-cpp'>#endif</span>
<a name="line-69"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Monad</span><span class='hs-varop'>.</span><span class='hs-conid'>STM</span> <span class='hs-layout'>(</span><span class='hs-conid'>STM</span><span class='hs-layout'>,</span> <span class='hs-varid'>retry</span><span class='hs-layout'>)</span>
<a name="line-70"></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'>STM</span><span class='hs-varop'>.</span><span class='hs-conid'>TVar</span>
<a name="line-71"></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'>STM</span><span class='hs-varop'>.</span><span class='hs-conid'>TChan</span> <span class='hs-comment'>-- N.B., GHC only</span>
<a name="line-72"></a>
<a name="line-73"></a><span class='hs-comment'>-- N.B., we need a Custom cabal build-type for this to work.</span>
<a name="line-74"></a><span class='hs-cpp'>#ifdef __HADDOCK__</span>
<a name="line-75"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Monad</span><span class='hs-varop'>.</span><span class='hs-conid'>STM</span> <span class='hs-layout'>(</span><span class='hs-varid'>atomically</span><span class='hs-layout'>)</span>
<a name="line-76"></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'>unsafePerformIO</span><span class='hs-layout'>)</span>
<a name="line-77"></a><span class='hs-cpp'>#endif</span>
<a name="line-78"></a><span class='hs-comment'>----------------------------------------------------------------</span>
<a name="line-79"></a>
<a name="line-80"></a><a name="TBMChan"></a><span class='hs-comment'>-- | @TBMChan@ is an abstract type representing a bounded closeable</span>
<a name="line-81"></a><a name="TBMChan"></a><span class='hs-comment'>-- FIFO channel.</span>
<a name="line-82"></a><a name="TBMChan"></a><span class='hs-keyword'>data</span> <span class='hs-conid'>TBMChan</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>TBMChan</span>
<a name="line-83"></a> <span class='hs-comment'>{-# UNPACK #-}</span> <span class='hs-varop'>!</span><span class='hs-layout'>(</span><span class='hs-conid'>TVar</span> <span class='hs-conid'>Bool</span><span class='hs-layout'>)</span>
<a name="line-84"></a> <span class='hs-comment'>{-# UNPACK #-}</span> <span class='hs-varop'>!</span><span class='hs-layout'>(</span><span class='hs-conid'>TVar</span> <span class='hs-conid'>Int</span><span class='hs-layout'>)</span>
<a name="line-85"></a> <span class='hs-comment'>{-# UNPACK #-}</span> <span class='hs-varop'>!</span><span class='hs-layout'>(</span><span class='hs-conid'>TVar</span> <span class='hs-conid'>Int</span><span class='hs-layout'>)</span>
<a name="line-86"></a> <span class='hs-comment'>{-# UNPACK #-}</span> <span class='hs-varop'>!</span><span class='hs-layout'>(</span><span class='hs-conid'>TChan</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span>
<a name="line-87"></a> <span class='hs-keyword'>deriving</span> <span class='hs-layout'>(</span><span class='hs-conid'>Typeable</span><span class='hs-layout'>)</span>
<a name="line-88"></a><span class='hs-comment'>-- The components are:</span>
<a name="line-89"></a><span class='hs-comment'>-- * Whether the channel has been closed.</span>
<a name="line-90"></a><span class='hs-comment'>-- * How many free slots we /know/ we have available.</span>
<a name="line-91"></a><span class='hs-comment'>-- * How many slots have been freed up by successful reads since</span>
<a name="line-92"></a><span class='hs-comment'>-- the last time the slot count was synchronized by 'isFullTBChan'.</span>
<a name="line-93"></a><span class='hs-comment'>-- * The underlying TChan.</span>
<a name="line-94"></a>
<a name="line-95"></a>
<a name="line-96"></a><a name="newTBMChan"></a><span class='hs-comment'>-- | Build and returns a new instance of @TBMChan@ with the given</span>
<a name="line-97"></a><span class='hs-comment'>-- capacity. /N.B./, we do not verify the capacity is positive, but</span>
<a name="line-98"></a><span class='hs-comment'>-- if it is non-positive then 'writeTBMChan' will always retry and</span>
<a name="line-99"></a><span class='hs-comment'>-- 'isFullTBMChan' will always be true.</span>
<a name="line-100"></a><span class='hs-definition'>newTBMChan</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Int</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>STM</span> <span class='hs-layout'>(</span><span class='hs-conid'>TBMChan</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span>
<a name="line-101"></a><span class='hs-definition'>newTBMChan</span> <span class='hs-varid'>n</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-102"></a> <span class='hs-varid'>closed</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>newTVar</span> <span class='hs-conid'>False</span>
<a name="line-103"></a> <span class='hs-varid'>slots</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>newTVar</span> <span class='hs-varid'>n</span>
<a name="line-104"></a> <span class='hs-varid'>reads</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>newTVar</span> <span class='hs-num'>0</span>
<a name="line-105"></a> <span class='hs-varid'>chan</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>newTChan</span>
<a name="line-106"></a> <span class='hs-varid'>return</span> <span class='hs-layout'>(</span><span class='hs-conid'>TBMChan</span> <span class='hs-varid'>closed</span> <span class='hs-varid'>slots</span> <span class='hs-varid'>reads</span> <span class='hs-varid'>chan</span><span class='hs-layout'>)</span>
<a name="line-107"></a>
<a name="line-108"></a>
<a name="line-109"></a><a name="newTBMChanIO"></a><span class='hs-comment'>-- | @IO@ version of 'newTBMChan'. This is useful for creating</span>
<a name="line-110"></a><span class='hs-comment'>-- top-level @TBMChan@s using 'unsafePerformIO', because using</span>
<a name="line-111"></a><span class='hs-comment'>-- 'atomically' inside 'unsafePerformIO' isn't possible.</span>
<a name="line-112"></a><span class='hs-definition'>newTBMChanIO</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Int</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-layout'>(</span><span class='hs-conid'>TBMChan</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span>
<a name="line-113"></a><span class='hs-definition'>newTBMChanIO</span> <span class='hs-varid'>n</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-114"></a> <span class='hs-varid'>closed</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>newTVarIO</span> <span class='hs-conid'>False</span>
<a name="line-115"></a> <span class='hs-varid'>slots</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>newTVarIO</span> <span class='hs-varid'>n</span>
<a name="line-116"></a> <span class='hs-varid'>reads</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>newTVarIO</span> <span class='hs-num'>0</span>
<a name="line-117"></a> <span class='hs-varid'>chan</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>newTChanIO</span>
<a name="line-118"></a> <span class='hs-varid'>return</span> <span class='hs-layout'>(</span><span class='hs-conid'>TBMChan</span> <span class='hs-varid'>closed</span> <span class='hs-varid'>slots</span> <span class='hs-varid'>reads</span> <span class='hs-varid'>chan</span><span class='hs-layout'>)</span>
<a name="line-119"></a>
<a name="line-120"></a>
<a name="line-121"></a><a name="readTBMChan"></a><span class='hs-comment'>-- | Read the next value from the @TBMChan@, retrying if the channel</span>
<a name="line-122"></a><span class='hs-comment'>-- is empty (and not closed). We return @Nothing@ immediately if</span>
<a name="line-123"></a><span class='hs-comment'>-- the channel is closed and empty.</span>
<a name="line-124"></a><span class='hs-definition'>readTBMChan</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>TBMChan</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>STM</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-125"></a><span class='hs-definition'>readTBMChan</span> <span class='hs-layout'>(</span><span class='hs-conid'>TBMChan</span> <span class='hs-varid'>closed</span> <span class='hs-sel'>_slots</span> <span class='hs-varid'>reads</span> <span class='hs-varid'>chan</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-126"></a> <span class='hs-varid'>b</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>readTVar</span> <span class='hs-varid'>closed</span>
<a name="line-127"></a> <span class='hs-keyword'>if</span> <span class='hs-varid'>b</span>
<a name="line-128"></a> <span class='hs-keyword'>then</span> <span class='hs-keyword'>do</span>
<a name="line-129"></a> <span class='hs-varid'>mx</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>tryReadTChan</span> <span class='hs-varid'>chan</span>
<a name="line-130"></a> <span class='hs-keyword'>case</span> <span class='hs-varid'>mx</span> <span class='hs-keyword'>of</span>
<a name="line-131"></a> <span class='hs-conid'>Nothing</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>return</span> <span class='hs-varid'>mx</span>
<a name="line-132"></a> <span class='hs-conid'>Just</span> <span class='hs-sel'>_x</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyword'>do</span>
<a name="line-133"></a> <span class='hs-varid'>modifyTVar'</span> <span class='hs-varid'>reads</span> <span class='hs-layout'>(</span><span class='hs-num'>1</span> <span class='hs-varop'>+</span><span class='hs-layout'>)</span>
<a name="line-134"></a> <span class='hs-varid'>return</span> <span class='hs-varid'>mx</span>
<a name="line-135"></a> <span class='hs-keyword'>else</span> <span class='hs-keyword'>do</span>
<a name="line-136"></a> <span class='hs-varid'>x</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>readTChan</span> <span class='hs-varid'>chan</span>
<a name="line-137"></a> <span class='hs-varid'>modifyTVar'</span> <span class='hs-varid'>reads</span> <span class='hs-layout'>(</span><span class='hs-num'>1</span> <span class='hs-varop'>+</span><span class='hs-layout'>)</span>
<a name="line-138"></a> <span class='hs-varid'>return</span> <span class='hs-layout'>(</span><span class='hs-conid'>Just</span> <span class='hs-varid'>x</span><span class='hs-layout'>)</span>
<a name="line-139"></a><span class='hs-comment'>{-
<a name="line-140"></a>-- The above is slightly optimized over the clearer:
<a name="line-141"></a>readTBMChan (TBMChan closed _slots reads chan) =
<a name="line-142"></a> b <- readTVar closed
<a name="line-143"></a> b' <- isEmptyTChan chan
<a name="line-144"></a> if b && b'
<a name="line-145"></a> then return Nothing
<a name="line-146"></a> else do
<a name="line-147"></a> x <- readTChan chan
<a name="line-148"></a> modifyTVar' reads (1 +)
<a name="line-149"></a> return (Just x)
<a name="line-150"></a>-- TODO: compare Core and benchmarks; is the loss of clarity worth it?
<a name="line-151"></a>-}</span>
<a name="line-152"></a>
<a name="line-153"></a>
<a name="line-154"></a><a name="tryReadTBMChan"></a><span class='hs-comment'>-- | A version of 'readTBMChan' which does not retry. Instead it</span>
<a name="line-155"></a><span class='hs-comment'>-- returns @Just Nothing@ if the channel is open but no value is</span>
<a name="line-156"></a><span class='hs-comment'>-- available; it still returns @Nothing@ if the channel is closed</span>
<a name="line-157"></a><span class='hs-comment'>-- and empty.</span>
<a name="line-158"></a><span class='hs-definition'>tryReadTBMChan</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>TBMChan</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>STM</span> <span class='hs-layout'>(</span><span class='hs-conid'>Maybe</span> <span class='hs-layout'>(</span><span class='hs-conid'>Maybe</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span>
<a name="line-159"></a><span class='hs-definition'>tryReadTBMChan</span> <span class='hs-layout'>(</span><span class='hs-conid'>TBMChan</span> <span class='hs-varid'>closed</span> <span class='hs-sel'>_slots</span> <span class='hs-varid'>reads</span> <span class='hs-varid'>chan</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-160"></a> <span class='hs-varid'>b</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>readTVar</span> <span class='hs-varid'>closed</span>
<a name="line-161"></a> <span class='hs-keyword'>if</span> <span class='hs-varid'>b</span>
<a name="line-162"></a> <span class='hs-keyword'>then</span> <span class='hs-keyword'>do</span>
<a name="line-163"></a> <span class='hs-varid'>mx</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>tryReadTChan</span> <span class='hs-varid'>chan</span>
<a name="line-164"></a> <span class='hs-keyword'>case</span> <span class='hs-varid'>mx</span> <span class='hs-keyword'>of</span>
<a name="line-165"></a> <span class='hs-conid'>Nothing</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>return</span> <span class='hs-conid'>Nothing</span>
<a name="line-166"></a> <span class='hs-conid'>Just</span> <span class='hs-sel'>_x</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyword'>do</span>
<a name="line-167"></a> <span class='hs-varid'>modifyTVar'</span> <span class='hs-varid'>reads</span> <span class='hs-layout'>(</span><span class='hs-num'>1</span> <span class='hs-varop'>+</span><span class='hs-layout'>)</span>
<a name="line-168"></a> <span class='hs-varid'>return</span> <span class='hs-layout'>(</span><span class='hs-conid'>Just</span> <span class='hs-varid'>mx</span><span class='hs-layout'>)</span>
<a name="line-169"></a> <span class='hs-keyword'>else</span> <span class='hs-keyword'>do</span>
<a name="line-170"></a> <span class='hs-varid'>mx</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>tryReadTChan</span> <span class='hs-varid'>chan</span>
<a name="line-171"></a> <span class='hs-keyword'>case</span> <span class='hs-varid'>mx</span> <span class='hs-keyword'>of</span>
<a name="line-172"></a> <span class='hs-conid'>Nothing</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>return</span> <span class='hs-layout'>(</span><span class='hs-conid'>Just</span> <span class='hs-varid'>mx</span><span class='hs-layout'>)</span>
<a name="line-173"></a> <span class='hs-conid'>Just</span> <span class='hs-sel'>_x</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyword'>do</span>
<a name="line-174"></a> <span class='hs-varid'>modifyTVar'</span> <span class='hs-varid'>reads</span> <span class='hs-layout'>(</span><span class='hs-num'>1</span> <span class='hs-varop'>+</span><span class='hs-layout'>)</span>
<a name="line-175"></a> <span class='hs-varid'>return</span> <span class='hs-layout'>(</span><span class='hs-conid'>Just</span> <span class='hs-varid'>mx</span><span class='hs-layout'>)</span>
<a name="line-176"></a><span class='hs-comment'>{-
<a name="line-177"></a>-- The above is slightly optimized over the clearer:
<a name="line-178"></a>tryReadTBMChan (TBMChan closed _slots reads chan) =
<a name="line-179"></a> b <- readTVar closed
<a name="line-180"></a> b' <- isEmptyTChan chan
<a name="line-181"></a> if b && b'
<a name="line-182"></a> then return Nothing
<a name="line-183"></a> else do
<a name="line-184"></a> mx <- tryReadTBMChan chan
<a name="line-185"></a> case mx of
<a name="line-186"></a> Nothing -> return (Just mx)
<a name="line-187"></a> Just _x -> do
<a name="line-188"></a> modifyTVar' reads (1 +)
<a name="line-189"></a> return (Just mx)
<a name="line-190"></a>-- TODO: compare Core and benchmarks; is the loss of clarity worth it?
<a name="line-191"></a>-}</span>
<a name="line-192"></a>
<a name="line-193"></a>
<a name="line-194"></a><a name="peekTBMChan"></a><span class='hs-comment'>-- | Get the next value from the @TBMChan@ without removing it,</span>
<a name="line-195"></a><span class='hs-comment'>-- retrying if the channel is empty.</span>
<a name="line-196"></a><span class='hs-definition'>peekTBMChan</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>TBMChan</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>STM</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-197"></a><span class='hs-definition'>peekTBMChan</span> <span class='hs-layout'>(</span><span class='hs-conid'>TBMChan</span> <span class='hs-varid'>closed</span> <span class='hs-sel'>_slots</span> <span class='hs-sel'>_reads</span> <span class='hs-varid'>chan</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-198"></a> <span class='hs-varid'>b</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>readTVar</span> <span class='hs-varid'>closed</span>
<a name="line-199"></a> <span class='hs-keyword'>if</span> <span class='hs-varid'>b</span>
<a name="line-200"></a> <span class='hs-keyword'>then</span> <span class='hs-keyword'>do</span>
<a name="line-201"></a> <span class='hs-varid'>b'</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>isEmptyTChan</span> <span class='hs-varid'>chan</span>
<a name="line-202"></a> <span class='hs-keyword'>if</span> <span class='hs-varid'>b'</span>
<a name="line-203"></a> <span class='hs-keyword'>then</span> <span class='hs-varid'>return</span> <span class='hs-conid'>Nothing</span>
<a name="line-204"></a> <span class='hs-keyword'>else</span> <span class='hs-conid'>Just</span> <span class='hs-varop'><$></span> <span class='hs-varid'>peekTChan</span> <span class='hs-varid'>chan</span>
<a name="line-205"></a> <span class='hs-keyword'>else</span> <span class='hs-conid'>Just</span> <span class='hs-varop'><$></span> <span class='hs-varid'>peekTChan</span> <span class='hs-varid'>chan</span>
<a name="line-206"></a><span class='hs-comment'>{-
<a name="line-207"></a>-- The above is lazier reading from @chan@ than the clearer:
<a name="line-208"></a>peekTBMChan (TBMChan closed _slots _reads chan) = do
<a name="line-209"></a> b <- isEmptyTChan chan
<a name="line-210"></a> b' <- readTVar closed
<a name="line-211"></a> if b && b'
<a name="line-212"></a> then return Nothing
<a name="line-213"></a> else Just <$> peekTChan chan
<a name="line-214"></a>-- TODO: compare Core and benchmarks; is the loss of clarity worth it?
<a name="line-215"></a>-}</span>
<a name="line-216"></a>
<a name="line-217"></a>
<a name="line-218"></a><a name="tryPeekTBMChan"></a><span class='hs-comment'>-- | A version of 'peekTBMChan' which does not retry. Instead it</span>
<a name="line-219"></a><span class='hs-comment'>-- returns @Just Nothing@ if the channel is open but no value is</span>
<a name="line-220"></a><span class='hs-comment'>-- available; it still returns @Nothing@ if the channel is closed</span>
<a name="line-221"></a><span class='hs-comment'>-- and empty.</span>
<a name="line-222"></a><span class='hs-definition'>tryPeekTBMChan</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>TBMChan</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>STM</span> <span class='hs-layout'>(</span><span class='hs-conid'>Maybe</span> <span class='hs-layout'>(</span><span class='hs-conid'>Maybe</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span>
<a name="line-223"></a><span class='hs-definition'>tryPeekTBMChan</span> <span class='hs-layout'>(</span><span class='hs-conid'>TBMChan</span> <span class='hs-varid'>closed</span> <span class='hs-sel'>_slots</span> <span class='hs-sel'>_reads</span> <span class='hs-varid'>chan</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-224"></a> <span class='hs-varid'>b</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>readTVar</span> <span class='hs-varid'>closed</span>
<a name="line-225"></a> <span class='hs-keyword'>if</span> <span class='hs-varid'>b</span>
<a name="line-226"></a> <span class='hs-keyword'>then</span> <span class='hs-varid'>fmap</span> <span class='hs-conid'>Just</span> <span class='hs-varop'><$></span> <span class='hs-varid'>tryPeekTChan</span> <span class='hs-varid'>chan</span>
<a name="line-227"></a> <span class='hs-keyword'>else</span> <span class='hs-conid'>Just</span> <span class='hs-varop'><$></span> <span class='hs-varid'>tryPeekTChan</span> <span class='hs-varid'>chan</span>
<a name="line-228"></a><span class='hs-comment'>{-
<a name="line-229"></a>-- The above is lazier reading from @chan@ (and removes an extraneous isEmptyTChan when using the compatibility layer) than the clearer:
<a name="line-230"></a>tryPeekTBMChan (TBMChan closed _slots _reads chan) = do
<a name="line-231"></a> b <- isEmptyTChan chan
<a name="line-232"></a> b' <- readTVar closed
<a name="line-233"></a> if b && b'
<a name="line-234"></a> then return Nothing
<a name="line-235"></a> else Just <$> tryPeekTChan chan
<a name="line-236"></a>-- TODO: compare Core and benchmarks; is the loss of clarity worth it?
<a name="line-237"></a>-}</span>
<a name="line-238"></a>
<a name="line-239"></a>
<a name="line-240"></a><a name="writeTBMChan"></a><span class='hs-comment'>-- | Write a value to a @TBMChan@, retrying if the channel is full.</span>
<a name="line-241"></a><span class='hs-comment'>-- If the channel is closed then the value is silently discarded.</span>
<a name="line-242"></a><span class='hs-comment'>-- Use 'isClosedTBMChan' to determine if the channel is closed</span>
<a name="line-243"></a><span class='hs-comment'>-- before writing, as needed.</span>
<a name="line-244"></a><span class='hs-definition'>writeTBMChan</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>TBMChan</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'>STM</span> <span class='hs-conid'>()</span>
<a name="line-245"></a><span class='hs-definition'>writeTBMChan</span> <span class='hs-varid'>self</span><span class='hs-keyglyph'>@</span><span class='hs-layout'>(</span><span class='hs-conid'>TBMChan</span> <span class='hs-varid'>closed</span> <span class='hs-varid'>slots</span> <span class='hs-sel'>_reads</span> <span class='hs-varid'>chan</span><span class='hs-layout'>)</span> <span class='hs-varid'>x</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-246"></a> <span class='hs-varid'>b</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>readTVar</span> <span class='hs-varid'>closed</span>
<a name="line-247"></a> <span class='hs-keyword'>if</span> <span class='hs-varid'>b</span>
<a name="line-248"></a> <span class='hs-keyword'>then</span> <span class='hs-varid'>return</span> <span class='hs-conid'>()</span> <span class='hs-comment'>-- Discard silently</span>
<a name="line-249"></a> <span class='hs-keyword'>else</span> <span class='hs-keyword'>do</span>
<a name="line-250"></a> <span class='hs-varid'>n</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>estimateFreeSlotsTBMChan</span> <span class='hs-varid'>self</span>
<a name="line-251"></a> <span class='hs-keyword'>if</span> <span class='hs-varid'>n</span> <span class='hs-varop'><=</span> <span class='hs-num'>0</span>
<a name="line-252"></a> <span class='hs-keyword'>then</span> <span class='hs-varid'>retry</span>
<a name="line-253"></a> <span class='hs-keyword'>else</span> <span class='hs-keyword'>do</span>
<a name="line-254"></a> <span class='hs-varid'>writeTVar</span> <span class='hs-varid'>slots</span> <span class='hs-varop'>$!</span> <span class='hs-varid'>n</span> <span class='hs-comment'>-</span> <span class='hs-num'>1</span>
<a name="line-255"></a> <span class='hs-varid'>writeTChan</span> <span class='hs-varid'>chan</span> <span class='hs-varid'>x</span>
<a name="line-256"></a>
<a name="line-257"></a>
<a name="line-258"></a><a name="tryWriteTBMChan"></a><span class='hs-comment'>-- | A version of 'writeTBMChan' which does not retry. Returns @Just</span>
<a name="line-259"></a><span class='hs-comment'>-- True@ if the value was successfully written, @Just False@ if it</span>
<a name="line-260"></a><span class='hs-comment'>-- could not be written (but the channel was open), and @Nothing@</span>
<a name="line-261"></a><span class='hs-comment'>-- if it was discarded (i.e., the channel was closed).</span>
<a name="line-262"></a><span class='hs-definition'>tryWriteTBMChan</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>TBMChan</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'>STM</span> <span class='hs-layout'>(</span><span class='hs-conid'>Maybe</span> <span class='hs-conid'>Bool</span><span class='hs-layout'>)</span>
<a name="line-263"></a><span class='hs-definition'>tryWriteTBMChan</span> <span class='hs-varid'>self</span><span class='hs-keyglyph'>@</span><span class='hs-layout'>(</span><span class='hs-conid'>TBMChan</span> <span class='hs-varid'>closed</span> <span class='hs-varid'>slots</span> <span class='hs-sel'>_reads</span> <span class='hs-varid'>chan</span><span class='hs-layout'>)</span> <span class='hs-varid'>x</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-264"></a> <span class='hs-varid'>b</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>readTVar</span> <span class='hs-varid'>closed</span>
<a name="line-265"></a> <span class='hs-keyword'>if</span> <span class='hs-varid'>b</span>
<a name="line-266"></a> <span class='hs-keyword'>then</span> <span class='hs-varid'>return</span> <span class='hs-conid'>Nothing</span>
<a name="line-267"></a> <span class='hs-keyword'>else</span> <span class='hs-keyword'>do</span>
<a name="line-268"></a> <span class='hs-varid'>n</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>estimateFreeSlotsTBMChan</span> <span class='hs-varid'>self</span>
<a name="line-269"></a> <span class='hs-keyword'>if</span> <span class='hs-varid'>n</span> <span class='hs-varop'><=</span> <span class='hs-num'>0</span>
<a name="line-270"></a> <span class='hs-keyword'>then</span> <span class='hs-varid'>return</span> <span class='hs-layout'>(</span><span class='hs-conid'>Just</span> <span class='hs-conid'>False</span><span class='hs-layout'>)</span>
<a name="line-271"></a> <span class='hs-keyword'>else</span> <span class='hs-keyword'>do</span>
<a name="line-272"></a> <span class='hs-varid'>writeTVar</span> <span class='hs-varid'>slots</span> <span class='hs-varop'>$!</span> <span class='hs-varid'>n</span> <span class='hs-comment'>-</span> <span class='hs-num'>1</span>
<a name="line-273"></a> <span class='hs-varid'>writeTChan</span> <span class='hs-varid'>chan</span> <span class='hs-varid'>x</span>
<a name="line-274"></a> <span class='hs-varid'>return</span> <span class='hs-layout'>(</span><span class='hs-conid'>Just</span> <span class='hs-conid'>True</span><span class='hs-layout'>)</span>
<a name="line-275"></a>
<a name="line-276"></a>
<a name="line-277"></a><a name="unGetTBMChan"></a><span class='hs-comment'>-- | Put a data item back onto a channel, where it will be the next</span>
<a name="line-278"></a><span class='hs-comment'>-- item read. If the channel is closed then the value is silently</span>
<a name="line-279"></a><span class='hs-comment'>-- discarded; you can use 'peekTBMChan' to circumvent this in certain</span>
<a name="line-280"></a><span class='hs-comment'>-- circumstances. /N.B./, this could allow the channel to temporarily</span>
<a name="line-281"></a><span class='hs-comment'>-- become longer than the specified limit, which is necessary to</span>
<a name="line-282"></a><span class='hs-comment'>-- ensure that the item is indeed the next one read.</span>
<a name="line-283"></a><span class='hs-definition'>unGetTBMChan</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>TBMChan</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'>STM</span> <span class='hs-conid'>()</span>
<a name="line-284"></a><span class='hs-definition'>unGetTBMChan</span> <span class='hs-layout'>(</span><span class='hs-conid'>TBMChan</span> <span class='hs-varid'>closed</span> <span class='hs-varid'>slots</span> <span class='hs-sel'>_reads</span> <span class='hs-varid'>chan</span><span class='hs-layout'>)</span> <span class='hs-varid'>x</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-285"></a> <span class='hs-varid'>b</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>readTVar</span> <span class='hs-varid'>closed</span>
<a name="line-286"></a> <span class='hs-keyword'>if</span> <span class='hs-varid'>b</span>
<a name="line-287"></a> <span class='hs-keyword'>then</span> <span class='hs-varid'>return</span> <span class='hs-conid'>()</span> <span class='hs-comment'>-- Discard silently</span>
<a name="line-288"></a> <span class='hs-keyword'>else</span> <span class='hs-keyword'>do</span>
<a name="line-289"></a> <span class='hs-varid'>modifyTVar'</span> <span class='hs-varid'>slots</span> <span class='hs-layout'>(</span><span class='hs-varid'>subtract</span> <span class='hs-num'>1</span><span class='hs-layout'>)</span>
<a name="line-290"></a> <span class='hs-varid'>unGetTChan</span> <span class='hs-varid'>chan</span> <span class='hs-varid'>x</span>
<a name="line-291"></a>
<a name="line-292"></a>
<a name="line-293"></a><a name="closeTBMChan"></a><span class='hs-comment'>-- | Closes the @TBMChan@, preventing any further writes.</span>
<a name="line-294"></a><span class='hs-definition'>closeTBMChan</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>TBMChan</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>STM</span> <span class='hs-conid'>()</span>
<a name="line-295"></a><span class='hs-definition'>closeTBMChan</span> <span class='hs-layout'>(</span><span class='hs-conid'>TBMChan</span> <span class='hs-varid'>closed</span> <span class='hs-sel'>_slots</span> <span class='hs-sel'>_reads</span> <span class='hs-sel'>_chan</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span>
<a name="line-296"></a> <span class='hs-varid'>writeTVar</span> <span class='hs-varid'>closed</span> <span class='hs-conid'>True</span>
<a name="line-297"></a>
<a name="line-298"></a>
<a name="line-299"></a><a name="isClosedTBMChan"></a><span class='hs-comment'>-- | Returns @True@ if the supplied @TBMChan@ has been closed.</span>
<a name="line-300"></a><span class='hs-definition'>isClosedTBMChan</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>TBMChan</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>STM</span> <span class='hs-conid'>Bool</span>
<a name="line-301"></a><span class='hs-definition'>isClosedTBMChan</span> <span class='hs-layout'>(</span><span class='hs-conid'>TBMChan</span> <span class='hs-varid'>closed</span> <span class='hs-sel'>_slots</span> <span class='hs-sel'>_reads</span> <span class='hs-sel'>_chan</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span>
<a name="line-302"></a> <span class='hs-varid'>readTVar</span> <span class='hs-varid'>closed</span>
<a name="line-303"></a>
<a name="line-304"></a><span class='hs-comment'>{-
<a name="line-305"></a>-- | Returns @True@ if the supplied @TBMChan@ has been closed.
<a name="line-306"></a>isClosedTBMChanIO :: TBMChan a -> IO Bool
<a name="line-307"></a>isClosedTBMChanIO (TBMChan closed _slots _reads _chan) =
<a name="line-308"></a> readTVarIO closed
<a name="line-309"></a>-}</span>
<a name="line-310"></a>
<a name="line-311"></a>
<a name="line-312"></a><a name="isEmptyTBMChan"></a><span class='hs-comment'>-- | Returns @True@ if the supplied @TBMChan@ is empty (i.e., has</span>
<a name="line-313"></a><span class='hs-comment'>-- no elements). /N.B./, a @TBMChan@ can be both ``empty'' and</span>
<a name="line-314"></a><span class='hs-comment'>-- ``full'' at the same time, if the initial limit was non-positive.</span>
<a name="line-315"></a><span class='hs-definition'>isEmptyTBMChan</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>TBMChan</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>STM</span> <span class='hs-conid'>Bool</span>
<a name="line-316"></a><span class='hs-definition'>isEmptyTBMChan</span> <span class='hs-layout'>(</span><span class='hs-conid'>TBMChan</span> <span class='hs-sel'>_closed</span> <span class='hs-sel'>_slots</span> <span class='hs-sel'>_reads</span> <span class='hs-varid'>chan</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span>
<a name="line-317"></a> <span class='hs-varid'>isEmptyTChan</span> <span class='hs-varid'>chan</span>
<a name="line-318"></a>
<a name="line-319"></a>
<a name="line-320"></a><a name="isFullTBMChan"></a><span class='hs-comment'>-- | Returns @True@ if the supplied @TBMChan@ is full (i.e., is</span>
<a name="line-321"></a><span class='hs-comment'>-- over its limit). /N.B./, a @TBMChan@ can be both ``empty'' and</span>
<a name="line-322"></a><span class='hs-comment'>-- ``full'' at the same time, if the initial limit was non-positive.</span>
<a name="line-323"></a><span class='hs-comment'>-- /N.B./, a @TBMChan@ may still be full after reading, if</span>
<a name="line-324"></a><span class='hs-comment'>-- 'unGetTBMChan' was used to go over the initial limit.</span>
<a name="line-325"></a><span class='hs-comment'>--</span>
<a name="line-326"></a><span class='hs-comment'>-- This is equivalent to: @liftM (<= 0) estimateFreeSlotsTBMChan@</span>
<a name="line-327"></a><span class='hs-definition'>isFullTBMChan</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>TBMChan</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>STM</span> <span class='hs-conid'>Bool</span>
<a name="line-328"></a><span class='hs-definition'>isFullTBMChan</span> <span class='hs-layout'>(</span><span class='hs-conid'>TBMChan</span> <span class='hs-sel'>_closed</span> <span class='hs-varid'>slots</span> <span class='hs-varid'>reads</span> <span class='hs-sel'>_chan</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-329"></a> <span class='hs-varid'>n</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>readTVar</span> <span class='hs-varid'>slots</span>
<a name="line-330"></a> <span class='hs-keyword'>if</span> <span class='hs-varid'>n</span> <span class='hs-varop'><=</span> <span class='hs-num'>0</span>
<a name="line-331"></a> <span class='hs-keyword'>then</span> <span class='hs-keyword'>do</span>
<a name="line-332"></a> <span class='hs-varid'>m</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>readTVar</span> <span class='hs-varid'>reads</span>
<a name="line-333"></a> <span class='hs-keyword'>let</span> <span class='hs-varid'>n'</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>n</span> <span class='hs-varop'>+</span> <span class='hs-varid'>m</span>
<a name="line-334"></a> <span class='hs-varid'>writeTVar</span> <span class='hs-varid'>slots</span> <span class='hs-varop'>$!</span> <span class='hs-varid'>n'</span>
<a name="line-335"></a> <span class='hs-varid'>writeTVar</span> <span class='hs-varid'>reads</span> <span class='hs-num'>0</span>
<a name="line-336"></a> <span class='hs-varid'>return</span> <span class='hs-varop'>$!</span> <span class='hs-varid'>n'</span> <span class='hs-varop'><=</span> <span class='hs-num'>0</span>
<a name="line-337"></a> <span class='hs-keyword'>else</span> <span class='hs-varid'>return</span> <span class='hs-conid'>False</span>
<a name="line-338"></a>
<a name="line-339"></a>
<a name="line-340"></a><a name="estimateFreeSlotsTBMChan"></a><span class='hs-comment'>-- | Estimate the number of free slots. If the result is positive,</span>
<a name="line-341"></a><span class='hs-comment'>-- then it's a minimum bound; if it's non-positive then it's exact.</span>
<a name="line-342"></a><span class='hs-comment'>-- It will only be negative if the initial limit was negative or</span>
<a name="line-343"></a><span class='hs-comment'>-- if 'unGetTBMChan' was used to go over the initial limit.</span>
<a name="line-344"></a><span class='hs-comment'>--</span>
<a name="line-345"></a><span class='hs-comment'>-- This function always contends with writers, but only contends</span>
<a name="line-346"></a><span class='hs-comment'>-- with readers when it has to; compare against 'freeSlotsTBMChan'.</span>
<a name="line-347"></a><span class='hs-definition'>estimateFreeSlotsTBMChan</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>TBMChan</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>STM</span> <span class='hs-conid'>Int</span>
<a name="line-348"></a><span class='hs-definition'>estimateFreeSlotsTBMChan</span> <span class='hs-layout'>(</span><span class='hs-conid'>TBMChan</span> <span class='hs-sel'>_closed</span> <span class='hs-varid'>slots</span> <span class='hs-varid'>reads</span> <span class='hs-sel'>_chan</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-349"></a> <span class='hs-varid'>n</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>readTVar</span> <span class='hs-varid'>slots</span>
<a name="line-350"></a> <span class='hs-keyword'>if</span> <span class='hs-varid'>n</span> <span class='hs-varop'>></span> <span class='hs-num'>0</span>
<a name="line-351"></a> <span class='hs-keyword'>then</span> <span class='hs-varid'>return</span> <span class='hs-varid'>n</span>
<a name="line-352"></a> <span class='hs-keyword'>else</span> <span class='hs-keyword'>do</span>
<a name="line-353"></a> <span class='hs-varid'>m</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>readTVar</span> <span class='hs-varid'>reads</span>
<a name="line-354"></a> <span class='hs-keyword'>let</span> <span class='hs-varid'>n'</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>n</span> <span class='hs-varop'>+</span> <span class='hs-varid'>m</span>
<a name="line-355"></a> <span class='hs-varid'>writeTVar</span> <span class='hs-varid'>slots</span> <span class='hs-varop'>$!</span> <span class='hs-varid'>n'</span>
<a name="line-356"></a> <span class='hs-varid'>writeTVar</span> <span class='hs-varid'>reads</span> <span class='hs-num'>0</span>
<a name="line-357"></a> <span class='hs-varid'>return</span> <span class='hs-varid'>n'</span>
<a name="line-358"></a>
<a name="line-359"></a>
<a name="line-360"></a><a name="freeSlotsTBMChan"></a><span class='hs-comment'>-- | Return the exact number of free slots. The result can be</span>
<a name="line-361"></a><span class='hs-comment'>-- negative if the initial limit was negative or if 'unGetTBMChan'</span>
<a name="line-362"></a><span class='hs-comment'>-- was used to go over the initial limit.</span>
<a name="line-363"></a><span class='hs-comment'>--</span>
<a name="line-364"></a><span class='hs-comment'>-- This function always contends with both readers and writers;</span>
<a name="line-365"></a><span class='hs-comment'>-- compare against 'estimateFreeSlotsTBMChan'.</span>
<a name="line-366"></a><span class='hs-definition'>freeSlotsTBMChan</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>TBMChan</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>STM</span> <span class='hs-conid'>Int</span>
<a name="line-367"></a><span class='hs-definition'>freeSlotsTBMChan</span> <span class='hs-layout'>(</span><span class='hs-conid'>TBMChan</span> <span class='hs-sel'>_closed</span> <span class='hs-varid'>slots</span> <span class='hs-varid'>reads</span> <span class='hs-sel'>_chan</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-368"></a> <span class='hs-varid'>n</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>readTVar</span> <span class='hs-varid'>slots</span>
<a name="line-369"></a> <span class='hs-varid'>m</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>readTVar</span> <span class='hs-varid'>reads</span>
<a name="line-370"></a> <span class='hs-keyword'>let</span> <span class='hs-varid'>n'</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>n</span> <span class='hs-varop'>+</span> <span class='hs-varid'>m</span>
<a name="line-371"></a> <span class='hs-varid'>writeTVar</span> <span class='hs-varid'>slots</span> <span class='hs-varop'>$!</span> <span class='hs-varid'>n'</span>
<a name="line-372"></a> <span class='hs-varid'>writeTVar</span> <span class='hs-varid'>reads</span> <span class='hs-num'>0</span>
<a name="line-373"></a> <span class='hs-varid'>return</span> <span class='hs-varid'>n'</span>
<a name="line-374"></a>
<a name="line-375"></a><span class='hs-comment'>----------------------------------------------------------------</span>
<a name="line-376"></a><span class='hs-comment'>----------------------------------------------------------- fin.</span>
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