<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html> <head> <!-- Generated by HsColour, http://code.haskell.org/~malcolm/hscolour/ --> <title>src/Control/Concurrent/STM/SSem.hs</title> <link type='text/css' rel='stylesheet' href='hscolour.css' /> </head> <body> <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.STM.SSem</span> <a name="line-4"></a><span class='hs-comment'>-- Copyright : (c) Chris Kuklewicz, 2012</span> <a name="line-5"></a><span class='hs-comment'>-- License : BSD-style</span> <a name="line-6"></a><span class='hs-comment'>-- </span> <a name="line-7"></a><span class='hs-comment'>-- Maintainer : haskell@list.mightyreason.com</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'>-- Very simple quantity semaphore.</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><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'>SSem</span><span class='hs-layout'>(</span><span class='hs-conid'>SSem</span><span class='hs-layout'>,</span> <span class='hs-varid'>new</span><span class='hs-layout'>,</span> <span class='hs-varid'>wait</span><span class='hs-layout'>,</span> <span class='hs-varid'>signal</span><span class='hs-layout'>,</span> <span class='hs-varid'>tryWait</span> <a name="line-15"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>waitN</span><span class='hs-layout'>,</span> <span class='hs-varid'>signalN</span><span class='hs-layout'>,</span> <span class='hs-varid'>tryWaitN</span> <a name="line-16"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>getValue</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span> <a name="line-17"></a> <a name="line-18"></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-19"></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><span class='hs-layout'>(</span><span class='hs-varid'>newTVar</span><span class='hs-layout'>,</span><span class='hs-varid'>readTVar</span><span class='hs-layout'>,</span><span class='hs-varid'>writeTVar</span><span class='hs-layout'>)</span> <a name="line-20"></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'>SSemInternals</span><span class='hs-layout'>(</span><span class='hs-conid'>SSem</span><span class='hs-layout'>(</span><span class='hs-conid'>SSem</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <a name="line-21"></a> <a name="line-22"></a><a name="new"></a><span class='hs-comment'>-- | Create a new semaphore with the given argument as the initially available quantity. This</span> <a name="line-23"></a><span class='hs-comment'>-- allows new semaphores to start with a negative, zero, or positive quantity.</span> <a name="line-24"></a><span class='hs-definition'>new</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-conid'>SSem</span> <a name="line-25"></a><span class='hs-definition'>new</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>fmap</span> <span class='hs-conid'>SSem</span> <span class='hs-varop'>.</span> <span class='hs-varid'>newTVar</span> <a name="line-26"></a> <a name="line-27"></a><a name="wait"></a><span class='hs-comment'>-- | Try to take a unit of value from the semaphore. This succeeds when the current quantity is</span> <a name="line-28"></a><span class='hs-comment'>-- positive, and then reduces the quantity by one. Otherwise this will 'retry'. This will never</span> <a name="line-29"></a><span class='hs-comment'>-- result in a negative quantity. If several threads are retying then which one succeeds next is</span> <a name="line-30"></a><span class='hs-comment'>-- undefined -- an unlucky thread might starve.</span> <a name="line-31"></a><span class='hs-definition'>wait</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>SSem</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>STM</span> <span class='hs-conid'>()</span> <a name="line-32"></a><span class='hs-definition'>wait</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>flip</span> <span class='hs-varid'>waitN</span> <span class='hs-num'>1</span> <a name="line-33"></a> <a name="line-34"></a><a name="waitN"></a><span class='hs-comment'>-- | Try to take the given value from the semaphore. This succeeds when the quantity is greater or</span> <a name="line-35"></a><span class='hs-comment'>-- equal to the given value, and then subtracts the given value from the quantity. Otherwise this</span> <a name="line-36"></a><span class='hs-comment'>-- will 'retry'. This will never result in a negative quantity. If several threads are retrying</span> <a name="line-37"></a><span class='hs-comment'>-- then which one succeeds next is undefined -- an unlucky thread might starve.</span> <a name="line-38"></a><span class='hs-definition'>waitN</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>SSem</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-conid'>()</span> <a name="line-39"></a><span class='hs-definition'>waitN</span> <span class='hs-layout'>(</span><span class='hs-conid'>SSem</span> <span class='hs-varid'>s</span><span class='hs-layout'>)</span> <span class='hs-varid'>i</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span> <a name="line-40"></a> <span class='hs-varid'>v</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>readTVar</span> <span class='hs-varid'>s</span> <a name="line-41"></a> <span class='hs-keyword'>if</span> <span class='hs-varid'>v</span> <span class='hs-varop'>>=</span> <span class='hs-varid'>i</span> <a name="line-42"></a> <span class='hs-keyword'>then</span> <span class='hs-varid'>writeTVar</span> <span class='hs-varid'>s</span> <span class='hs-varop'>$!</span> <span class='hs-varid'>v</span><span class='hs-comment'>-</span><span class='hs-varid'>i</span> <a name="line-43"></a> <span class='hs-keyword'>else</span> <span class='hs-varid'>retry</span> <a name="line-44"></a> <a name="line-45"></a><a name="signal"></a><span class='hs-comment'>-- | Signal that single unit of the semaphore is available. This increases the available quantity</span> <a name="line-46"></a><span class='hs-comment'>-- by one.</span> <a name="line-47"></a><span class='hs-definition'>signal</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>SSem</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>STM</span> <span class='hs-conid'>()</span> <a name="line-48"></a><span class='hs-definition'>signal</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>flip</span> <span class='hs-varid'>signalN</span> <span class='hs-num'>1</span> <a name="line-49"></a> <a name="line-50"></a><a name="signalN"></a><span class='hs-comment'>-- | Signal that many units of the semaphore are available. This changes the available quantity by</span> <a name="line-51"></a><span class='hs-comment'>-- adding the passed size.</span> <a name="line-52"></a><span class='hs-definition'>signalN</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>SSem</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-conid'>()</span> <a name="line-53"></a><span class='hs-definition'>signalN</span> <span class='hs-layout'>(</span><span class='hs-conid'>SSem</span> <span class='hs-varid'>s</span><span class='hs-layout'>)</span> <span class='hs-varid'>i</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span> <a name="line-54"></a> <span class='hs-varid'>v</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>readTVar</span> <span class='hs-varid'>s</span> <a name="line-55"></a> <span class='hs-varid'>writeTVar</span> <span class='hs-varid'>s</span> <span class='hs-varop'>$!</span> <span class='hs-varid'>v</span><span class='hs-varop'>+</span><span class='hs-varid'>i</span> <a name="line-56"></a> <a name="line-57"></a><a name="tryWait"></a><span class='hs-comment'>-- | Non-retrying version of 'wait'. `tryWait s` is defined as `tryN s 1`</span> <a name="line-58"></a><span class='hs-definition'>tryWait</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>SSem</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'>Int</span><span class='hs-layout'>)</span> <a name="line-59"></a><span class='hs-definition'>tryWait</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>flip</span> <span class='hs-varid'>tryWaitN</span> <span class='hs-num'>1</span> <a name="line-60"></a> <a name="line-61"></a><a name="tryWaitN"></a><span class='hs-comment'>-- | Non-retrying version of waitN. It either takes the quantity from the semaphore like</span> <a name="line-62"></a><span class='hs-comment'>-- waitN and returns `Just value taken` or finds insufficient quantity to take and returns</span> <a name="line-63"></a><span class='hs-comment'>-- Nothing</span> <a name="line-64"></a><span class='hs-definition'>tryWaitN</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>SSem</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'>Maybe</span> <span class='hs-conid'>Int</span><span class='hs-layout'>)</span> <a name="line-65"></a><span class='hs-definition'>tryWaitN</span> <span class='hs-layout'>(</span><span class='hs-conid'>SSem</span> <span class='hs-varid'>s</span><span class='hs-layout'>)</span> <span class='hs-varid'>i</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span> <a name="line-66"></a> <span class='hs-varid'>v</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>readTVar</span> <span class='hs-varid'>s</span> <a name="line-67"></a> <span class='hs-keyword'>if</span> <span class='hs-varid'>v</span> <span class='hs-varop'>>=</span> <span class='hs-varid'>i</span> <a name="line-68"></a> <span class='hs-keyword'>then</span> <span class='hs-keyword'>do</span> <span class='hs-varid'>writeTVar</span> <span class='hs-varid'>s</span> <span class='hs-varop'>$!</span> <span class='hs-varid'>v</span><span class='hs-comment'>-</span><span class='hs-varid'>i</span> <a name="line-69"></a> <span class='hs-varid'>return</span> <span class='hs-layout'>(</span><span class='hs-conid'>Just</span> <span class='hs-varid'>i</span><span class='hs-layout'>)</span> <a name="line-70"></a> <span class='hs-keyword'>else</span> <span class='hs-varid'>return</span> <span class='hs-conid'>Nothing</span> <a name="line-71"></a> <a name="line-72"></a><a name="getValue"></a><span class='hs-comment'>-- | Return the current quantity in the semaphore. This is potentially useful in a larger STM</span> <a name="line-73"></a><span class='hs-comment'>-- transaciton and less useful as `atomically getValueSem :: IO Int` due to race conditions.</span> <a name="line-74"></a><span class='hs-definition'>getValue</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>SSem</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>STM</span> <span class='hs-conid'>Int</span> <a name="line-75"></a><span class='hs-definition'>getValue</span> <span class='hs-layout'>(</span><span class='hs-conid'>SSem</span> <span class='hs-varid'>s</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>readTVar</span> <span class='hs-varid'>s</span> </pre></body> </html>
