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<h3>
Marge Bot pushed to branch master
at <a href="https://gitlab.haskell.org/ghc/ghc">Glasgow Haskell Compiler / GHC</a>
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Commits:
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<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/b26cd86795d86850bfa97aa020d0a46b8ac043da">b26cd867</a></strong>
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<span>by David Feuer</span>
<i>at 2020-09-19T15:51:44-04:00</i>
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<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Unpack the MVar in Compact
The `MVar` lock in `Compact` was unnecessarily lazy, creating an extra indirection and wasting two words. Make it strict.</pre>
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<h4>1 changed file:</h4>
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<a href="#02acfc8c310b49343a6198ad703b289a4347116c">
libraries/ghc-compact/GHC/Compact.hs
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<h4>Changes:</h4>
<li id="02acfc8c310b49343a6198ad703b289a4347116c">
<a href="https://gitlab.haskell.org/ghc/ghc/-/commit/b26cd86795d86850bfa97aa020d0a46b8ac043da#02acfc8c310b49343a6198ad703b289a4347116c"><strong>libraries/ghc-compact/GHC/Compact.hs</strong></a>
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<td class="line_content match " style="padding-left: 0.5em; padding-right: 0.5em; color: rgba(0,0,0,0.3);" bgcolor="#fafafa">@@ -136,7 +136,7 @@ import GHC.Types</td>
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<pre style="margin: 0;"> <span id="LC136" class="line" lang="haskell"><span class="c1" style="color: #998; font-style: italic;">-- If compaction encounters any of the above, a 'Control.Exception.CompactionFailed'</span></span>
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<pre style="margin: 0;"> <span id="LC137" class="line" lang="haskell"><span class="c1" style="color: #998; font-style: italic;">-- exception will be thrown by the compaction operation.</span></span>
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<pre style="margin: 0;"> <span id="LC138" class="line" lang="haskell"><span class="c1" style="color: #998; font-style: italic;">--</span></span>
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<pre style="margin: 0;">-<span id="LC139" class="line" lang="haskell"><span class="kr" style="font-weight: 600;">data</span> <span class="kt" style="color: #458; font-weight: 600;">Compact</span> <span class="n" style="color: #333;">a</span> <span class="o" style="font-weight: 600;">=</span> <span class="kt" style="color: #458; font-weight: 600;">Compact</span> <span class="kt" style="color: #458; font-weight: 600;">Compact</span><span class="o" style="font-weight: 600;">#</span> <span class="n" style="color: #333;">a</span> <span class="p">(</span><span class="kt" style="color: #458; font-weight: 600;">MVar</span> <span class="nb" style="color: #0086b3;">()</span><span class="p">)</span></span>
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<pre style="margin: 0;">+<span id="LC139" class="line" lang="haskell"><span class="kr" style="font-weight: 600;">data</span> <span class="kt" style="color: #458; font-weight: 600;">Compact</span> <span class="n" style="color: #333;">a</span> <span class="o" style="font-weight: 600;">=</span> <span class="kt" style="color: #458; font-weight: 600;">Compact</span> <span class="kt" style="color: #458; font-weight: 600;">Compact</span><span class="o" style="font-weight: 600;">#</span> <span class="n" style="color: #333;">a</span> <span class="o" style="font-weight: 600;"><span class="idiff left right">!</span></span><span class="p">(</span><span class="kt" style="color: #458; font-weight: 600;">MVar</span> <span class="nb" style="color: #0086b3;">()</span><span class="p">)</span></span>
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<pre style="margin: 0;"> <span id="LC140" class="line" lang="haskell"> <span class="c1" style="color: #998; font-style: italic;">-- we can *read* from a Compact without taking a lock, but only</span></span>
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<pre style="margin: 0;"> <span id="LC141" class="line" lang="haskell"> <span class="c1" style="color: #998; font-style: italic;">-- one thread can be writing to the compact at any given time.</span></span>
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<pre style="margin: 0;"> <span id="LC142" class="line" lang="haskell"> <span class="c1" style="color: #998; font-style: italic;">-- The MVar here is to enforce mutual exclusion among writers.</span></span>
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