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<title>Graphics/HGL/Internals/Flag.hs</title>
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<pre><a name="line-1"></a><span class='hs-comment'>-----------------------------------------------------------------------------</span>
<a name="line-2"></a><span class='hs-comment'>-- |</span>
<a name="line-3"></a><span class='hs-comment'>-- Module : Graphics.HGL.Internals.Flag</span>
<a name="line-4"></a><span class='hs-comment'>-- Copyright : (c) Alastair Reid, 1999-2003</span>
<a name="line-5"></a><span class='hs-comment'>-- License : BSD-style (see the file libraries/base/LICENSE)</span>
<a name="line-6"></a><span class='hs-comment'>-- </span>
<a name="line-7"></a><span class='hs-comment'>-- Maintainer : libraries@haskell.org</span>
<a name="line-8"></a><span class='hs-comment'>-- Stability : internal</span>
<a name="line-9"></a><span class='hs-comment'>-- Portability : non-portable (requires concurrency)</span>
<a name="line-10"></a><span class='hs-comment'>--</span>
<a name="line-11"></a><span class='hs-comment'>-- A simple graphics library.</span>
<a name="line-12"></a><span class='hs-comment'>--</span>
<a name="line-13"></a><span class='hs-comment'>-----------------------------------------------------------------------------</span>
<a name="line-14"></a>
<a name="line-15"></a><span class='hs-comment'>-- #hide</span>
<a name="line-16"></a><span class='hs-keyword'>module</span> <span class='hs-conid'>Graphics</span><span class='hs-varop'>.</span><span class='hs-conid'>HGL</span><span class='hs-varop'>.</span><span class='hs-conid'>Internals</span><span class='hs-varop'>.</span><span class='hs-conid'>Flag</span>
<a name="line-17"></a> <span class='hs-layout'>(</span> <span class='hs-conid'>Flag</span><span class='hs-layout'>,</span> <span class='hs-varid'>newFlag</span><span class='hs-layout'>,</span> <span class='hs-varid'>setFlag</span><span class='hs-layout'>,</span> <span class='hs-varid'>resetFlag</span>
<a name="line-18"></a> <span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-19"></a>
<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'>MVar</span>
<a name="line-21"></a> <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>
<a name="line-22"></a> <span class='hs-layout'>)</span>
<a name="line-23"></a>
<a name="line-24"></a><span class='hs-comment'>----------------------------------------------------------------</span>
<a name="line-25"></a><span class='hs-comment'>-- Interface</span>
<a name="line-26"></a><span class='hs-comment'>----------------------------------------------------------------</span>
<a name="line-27"></a>
<a name="line-28"></a><a name="Flag"></a><span class='hs-comment'>-- We maintain a list of blocked processes.</span>
<a name="line-29"></a><a name="Flag"></a><span class='hs-comment'>-- Blocked processes are "stored" in MVars; the outer MVar</span>
<a name="line-30"></a><a name="Flag"></a><span class='hs-comment'>-- is used to implement a critical section.</span>
<a name="line-31"></a><a name="Flag"></a><span class='hs-keyword'>newtype</span> <span class='hs-conid'>Flag</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Flag</span> <span class='hs-layout'>(</span><span class='hs-conid'>MVar</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>
<a name="line-32"></a>
<a name="line-33"></a><a name="newFlag"></a><span class='hs-definition'>newFlag</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>IO</span> <span class='hs-layout'>(</span><span class='hs-conid'>Flag</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span>
<a name="line-34"></a><a name="setFlag"></a><span class='hs-comment'>-- sets the flag, never blocks, never fails</span>
<a name="line-35"></a><span class='hs-definition'>setFlag</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Flag</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-36"></a><a name="resetFlag"></a><span class='hs-comment'>-- block until the flag is set (and reset it)</span>
<a name="line-37"></a><span class='hs-definition'>resetFlag</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Flag</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-38"></a>
<a name="line-39"></a><span class='hs-comment'>----------------------------------------------------------------</span>
<a name="line-40"></a><span class='hs-comment'>-- Implementation</span>
<a name="line-41"></a><span class='hs-comment'>----------------------------------------------------------------</span>
<a name="line-42"></a>
<a name="line-43"></a><span class='hs-definition'>newFlag</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-44"></a> <span class='hs-varid'>queue</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>newMVar</span> <span class='hs-conid'>[]</span>
<a name="line-45"></a> <span class='hs-varid'>return</span> <span class='hs-layout'>(</span><span class='hs-conid'>Flag</span> <span class='hs-varid'>queue</span><span class='hs-layout'>)</span>
<a name="line-46"></a>
<a name="line-47"></a><span class='hs-definition'>setFlag</span> <span class='hs-layout'>(</span><span class='hs-conid'>Flag</span> <span class='hs-varid'>queue</span><span class='hs-layout'>)</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-48"></a> <span class='hs-varid'>ps</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>takeMVar</span> <span class='hs-varid'>queue</span>
<a name="line-49"></a> <span class='hs-varid'>mapM_</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>\</span> <span class='hs-varid'>p</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>putMVar</span> <span class='hs-varid'>p</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-varid'>ps</span>
<a name="line-50"></a> <span class='hs-varid'>putMVar</span> <span class='hs-varid'>queue</span> <span class='hs-conid'>[]</span>
<a name="line-51"></a>
<a name="line-52"></a><span class='hs-definition'>resetFlag</span> <span class='hs-layout'>(</span><span class='hs-conid'>Flag</span> <span class='hs-varid'>queue</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-53"></a> <span class='hs-varid'>ps</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>takeMVar</span> <span class='hs-varid'>queue</span>
<a name="line-54"></a> <span class='hs-varid'>p</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>newEmptyMVar</span>
<a name="line-55"></a> <span class='hs-varid'>putMVar</span> <span class='hs-varid'>queue</span> <span class='hs-layout'>(</span><span class='hs-varid'>p</span><span class='hs-conop'>:</span><span class='hs-varid'>ps</span><span class='hs-layout'>)</span>
<a name="line-56"></a> <span class='hs-varid'>takeMVar</span> <span class='hs-varid'>p</span> <span class='hs-comment'>-- block</span>
<a name="line-57"></a>
<a name="line-58"></a><span class='hs-comment'>----------------------------------------------------------------</span>
<a name="line-59"></a><span class='hs-comment'>-- End</span>
<a name="line-60"></a><span class='hs-comment'>----------------------------------------------------------------</span>
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