<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Issue 3745: std::atomic_wait and its friends lack noexcept</title>
<meta property="og:title" content="Issue 3745: std::atomic_wait and its friends lack noexcept">
<meta property="og:description" content="C++ library issue. Status: C++23">
<meta property="og:url" content="https://cplusplus.github.io/LWG/issue3745.html">
<meta property="og:type" content="website">
<meta property="og:image" content="http://cplusplus.github.io/LWG/images/cpp_logo.png">
<meta property="og:image:alt" content="C++ logo">
<style>
  p {text-align:justify}
  li {text-align:justify}
  pre code.backtick::before { content: "`" }
  pre code.backtick::after { content: "`" }
  blockquote.note
  {
    background-color:#E0E0E0;
    padding-left: 15px;
    padding-right: 15px;
    padding-top: 1px;
    padding-bottom: 1px;
  }
  ins {background-color:#A0FFA0}
  del {background-color:#FFA0A0}
  table.issues-index { border: 1px solid; border-collapse: collapse; }
  table.issues-index th { text-align: center; padding: 4px; border: 1px solid; }
  table.issues-index td { padding: 4px; border: 1px solid; }
  table.issues-index td:nth-child(1) { text-align: right; }
  table.issues-index td:nth-child(2) { text-align: left; }
  table.issues-index td:nth-child(3) { text-align: left; }
  table.issues-index td:nth-child(4) { text-align: left; }
  table.issues-index td:nth-child(5) { text-align: center; }
  table.issues-index td:nth-child(6) { text-align: center; }
  table.issues-index td:nth-child(7) { text-align: left; }
  table.issues-index td:nth-child(5) span.no-pr { color: red; }
  @media (prefers-color-scheme: dark) {
     html {
        color: #ddd;
        background-color: black;
     }
     ins {
        background-color: #225522
     }
     del {
        background-color: #662222
     }
     a {
        color: #6af
     }
     a:visited {
        color: #6af
     }
     blockquote.note
     {
        background-color: rgba(255, 255, 255, .10)
     }
  }
</style>
</head>
<body>
<hr>
<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#C++23">C++23</a> status.</em></p>
<h3 id="3745"><a href="lwg-defects.html#3745">3745</a>. <code>std::atomic_wait</code> and its friends lack <code>noexcept</code></h3>
<p><b>Section:</b> 32.5.2 <a href="https://wg21.link/atomics.syn">[atomics.syn]</a> <b>Status:</b> <a href="lwg-active.html#C++23">C++23</a>
 <b>Submitter:</b> Jiang An <b>Opened:</b> 2022-07-25 <b>Last modified:</b> 2023-11-22</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View other</b> <a href="lwg-index-open.html#atomics.syn">active issues</a> in [atomics.syn].</p>
<p><b>View all other</b> <a href="lwg-index.html#atomics.syn">issues</a> in [atomics.syn].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++23">C++23</a> status.</p>
<p><b>Discussion:</b></p>
<p>
Currently function templates <code>std::atomic_wait</code>, <code>std::atomic_wait_explicit</code>, 
<code>std::atomic_notify_one</code>, and <code>std::atomic_notify_all</code> are not <code>noexcept</code> 
in the Working Draft, but the equivalent member functions are all <code>noexcept</code>. I think 
these function templates should be specified as <code>noexcept</code>, in order to be consistent 
with the <code>std::atomic_flag_*</code> free functions, the corresponding member functions, and 
other <code>std::atomic_*</code> function templates.
<p/>
Mainstream implementations (libc++, libstdc++, and MSVC STL) have already added <code>noexcept</code> 
to them.
</p>

<p><i>[2022-07-30; Daniel provides wording]</i></p>


<p><i>[2022-08-23; Reflector poll]</i></p>

<p>
Set status to Tentatively Ready after six votes in favour during reflector poll.
</p>
<p>
"Technically there's a difference between these and the member functions -
the pointer can be null - but we don't seem to have let that stop us
from adding noexcept to the rest of these functions."
</p>

<p><i>[2022-11-12 Approved at November 2022 meeting in Kona. Status changed: Voting &rarr; WP.]</i></p>



<p id="res-3745"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/N4910" title=" Working Draft, Standard for Programming Language C++">N4910</a>.
</p>

<ol>
<li><p>Modify 32.5.2 <a href="https://wg21.link/atomics.syn">[atomics.syn]</a>, header <code>&lt;atomic&gt;</code> synopsis, as indicated:</p>

<blockquote>
<pre>
[&hellip;]
template&lt;class T&gt;
  void atomic_wait(const volatile atomic&lt;T&gt;*, typename atomic&lt;T&gt;::value_type) <ins>noexcept</ins>;
template&lt;class T&gt;
  void atomic_wait(const atomic&lt;T&gt;*, typename atomic&lt;T&gt;::value_type) <ins>noexcept</ins>;
template&lt;class T&gt;
  void atomic_wait_explicit(const volatile atomic&lt;T&gt;*, typename atomic&lt;T&gt;::value_type,
                            memory_order) <ins>noexcept</ins>;
template&lt;class T&gt;
  void atomic_wait_explicit(const atomic&lt;T&gt;*, typename atomic&lt;T&gt;::value_type,
                            memory_order) <ins>noexcept</ins>;
template&lt;class T&gt;
  void atomic_notify_one(volatile atomic&lt;T&gt;*) <ins>noexcept</ins>;
template&lt;class T&gt;
  void atomic_notify_one(atomic&lt;T&gt;*) <ins>noexcept</ins>;
template&lt;class T&gt;
  void atomic_notify_all(volatile atomic&lt;T&gt;*) <ins>noexcept</ins>;
template&lt;class T&gt;
  void atomic_notify_all(atomic&lt;T&gt;*) <ins>noexcept</ins>;
[&hellip;]
</pre>
</blockquote>
</li>
</ol>





</body>
</html>
