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‎issue3409.html‎

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@@ -67,6 +67,8 @@ <h3 id="3409"><a href="lwg-active.html#3409">3409</a>. Too lax description of <c
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<b>Submitter:</b> Andrey Semashev <b>Opened:</b> 2020-02-27 <b>Last modified:</b> 2020-09-06</p>
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<p><b>Priority: </b>3
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</p>
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<p><b>View other</b> <a href="lwg-index-open.html#atomics.ref.ops">active issues</a> in [atomics.ref.ops].</p>
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<p><b>View all other</b> <a href="lwg-index.html#atomics.ref.ops">issues</a> in [atomics.ref.ops].</p>
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<p><b>View all issues with</b> <a href="lwg-status.html#New">New</a> status.</p>
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<p><b>Discussion:</b></p>
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<p>

‎issue4244.html‎

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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="utf-8">
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<title>Issue 4244: Whether the spuriously failed comparison applies to compare_exchange_strong is unclear</title>
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<meta property="og:title" content="Issue 4244: Whether the spuriously failed comparison applies to compare_exchange_strong is unclear">
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<meta property="og:description" content="C++ library issue. Status: New">
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<p><em>This page is a snapshot from the LWG issues list, see the <a href="lwg-active.html">Library Active Issues List</a> for more information and the meaning of <a href="lwg-active.html#New">New</a> status.</em></p>
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<h3 id="4244"><a href="lwg-active.html#4244">4244</a>. Whether the spuriously failed comparison applies to <code class='backtick'>compare_exchange_strong</code> is unclear</h3>
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<p><b>Section:</b> 32.5.7.2 <a href="https://wg21.link/atomics.ref.ops">[atomics.ref.ops]</a>, 32.5.8.2 <a href="https://wg21.link/atomics.types.operations">[atomics.types.operations]</a> <b>Status:</b> <a href="lwg-active.html#New">New</a>
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<b>Submitter:</b> jim x <b>Opened:</b> 2025-04-17 <b>Last modified:</b> 2025-04-21</p>
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<p><b>Priority: </b>Not Prioritized
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</p>
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<p><b>View other</b> <a href="lwg-index-open.html#atomics.ref.ops">active issues</a> in [atomics.ref.ops].</p>
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<p><b>View all other</b> <a href="lwg-index.html#atomics.ref.ops">issues</a> in [atomics.ref.ops].</p>
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<p><b>View all issues with</b> <a href="lwg-status.html#New">New</a> status.</p>
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<p><b>Discussion:</b></p>
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<p>
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Both <code class='backtick'>compare_exchange_strong</code> and <code class='backtick'>compare_exchange_weak</code> share the same specified rule
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</p>
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<blockquote style="border-left: 3px solid #ccc;padding-left: 15px;">
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<p>
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If and only if the comparison is <code class='backtick'>false</code> then, after the atomic operation, the value in
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<code class='backtick'>expected</code> is replaced by the value read from the value referenced by <code class='backtick'>*ptr</code> during the
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atomic comparison.
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</p>
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</blockquote>
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<p>
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However, there is a remark for the weak version
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</p>
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<blockquote style="border-left: 3px solid #ccc;padding-left: 15px;">
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<p>
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A weak compare-and-exchange operation may fail spuriously.
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</p>
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</blockquote>
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<p>
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That is, even when the contents of memory referred to by <code class='backtick'>expected</code> and <code class='backtick'>ptr</code> are equal,
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it may return <code class='backtick'>false</code> and store back to expected the same memory contents that were
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originally there.
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<p/>
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However, we don't explicitly say whether the strong version can have the spuriously failed
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comparison. The status quo is that we can only infer the point from the name, namely, the
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strong version should have a stronger guarantee than the weak version.
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<p/>
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<b>Suggested resolution:</b>
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<p/>
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Explicitly specify whether <code class='backtick'>compare_exchange_strong</code> can have the spurious failed comparison.
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</p>
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<p id="res-4244"><b>Proposed resolution:</b></p>
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</body>
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</html>

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