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<title>Issue 4349: task is not actually started lazily</title>
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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>
<h3 id="4349"><a href="lwg-active.html#4349">4349</a>. <code>task</code> is not actually started lazily</h3>
<p><b>Section:</b> 33.13.6.5 <a href="https://wg21.link/task.promise">[task.promise]</a> <b>Status:</b> <a href="lwg-active.html#New">New</a>
 <b>Submitter:</b> Dietmar Kühl <b>Opened:</b> 2025-09-01 <b>Last modified:</b> 2025-09-01</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View other</b> <a href="lwg-index-open.html#task.promise">active issues</a> in [task.promise].</p>
<p><b>View all other</b> <a href="lwg-index.html#task.promise">issues</a> in [task.promise].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#New">New</a> status.</p>
<p><b>Discussion:</b></p>
<p>
The wording for <code>task&lt;...&gt;::promise_type::initial_suspend</code>
in 33.13.6.5 <a href="https://wg21.link/task.promise">[task.promise]</a> paragraph 6
(second bullet) may imply that a task is eagerly started, i.e., that the
awaiter return from <code>initial_suspend()</code> immediately starts
the scheduling operation and cause the <code>task</code> to be resumed. At
the very least the second bullet of the wording should be clarified such
that the scheduling operation is only started when the coroutine gets
resumed.
</p>
<p>
An alternative resolution it have <code>initial_suspend()</code>
return <code>std::suspend_always</code> implicitly requiring that
the <code>task</code> gets <code>start()</code>ed from the correct
execution context. This approach has the advantage of avoiding
unnecessary scheduling operations for the likely common case when
<code>task</code>s are started from the correct context.
</p>


<p id="res-4349"><b>Proposed resolution:</b></p>
<p>
Change the declaration of <code>initial_suspend()</code> in the synopsis
of 33.13.6.5 <a href="https://wg21.link/task.promise">[task.promise]</a> to use
<code>suspend_always</code>, directly provide a definition, and add
various qualifiers:
<blockquote>
<pre>
namespace std::execution {
  template&lt;class T, class Environment&gt;
  class task&lt;T, Environment&gt;::promise_type {
    ...
    <del>auto</del><ins>static constexpr suspend_always</ins> initial_suspend() noexcept<del>;</del><ins>{ return {}; }</ins>
    ...
  };

}
</pre>
</blockquote>
</p>
<p>
Remove 33.13.6.5 <a href="https://wg21.link/task.promise">[task.promise]</a> paragraph 6 entirely:
<blockquote>
<pre><del>auto initial_suspend() noexcept;</del></pre>
<p><del>-6- <i>Returns:</i> An awaitable object of unspecified type ([expr.await]) whose member functions arrange for</del></p>
<p><del>-6.1- - the calling coroutine to be suspended,</del></p>
<p><del>-6.2- - the coroutine to be resumed on an execution agent of the execution resource associated with <code><i>SCHED</i>(*this)</code>.</del></p>
</blockquote>
</p>





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