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dietmarkuehldietmarkuehl
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add resolution for LWG4339: task's coroutine frame may be released late
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‎xml/issue4339.xml‎

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@@ -44,6 +44,78 @@ Thus, the <code>variant</code> can be replaced with an
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<resolution>
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<p>
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In <sref ref="[task.state]"/>, add
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exposition-only data members <code><i>result</i></code> and
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<code><i>error</i></code> to the exposition-only class
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<code><i>state</i></code>:
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<blockquote>
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<pre>
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namespace std::execution {
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template&lt;class T, class Environment&gt;
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template&lt;receiver Rcvr&gt;
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class task&lt;T, Environment&gt;::<i>state</i> { // <i>exposition only</i>
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...
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Environment <i>environment</i>; // <i>exposition only</i>
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<ins>optional&lt;T&gt; <i>result</i>; // <i>exposition only; present only if</i> is_void_v&lt;T&gt; <i>is</i> false</ins>
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<ins>exception_ptr <i>error</i>; // <i>exposition-only</i></ins>
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};
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}
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</pre>
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</blockquote>
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</p>
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<p>
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Remove the exposition-only data members
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<code><i>result</i></code> and <code><i>errors</i></code> from
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the class <code>promise_type</code> in
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<sref ref="[task.promise]"/>:
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<blockquote>
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<pre>
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namespace std::execution {
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template&lt;class T, class Environment&gt;
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class task&lt;T, Environment&gt;::promise_type {
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...
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stop_token_type <i>token</i>; // <i>exposition only</i>
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<del>optional&lt;T&gt; <i>result</i>; // <i>exposition only; present only if</i> is_void_v&lt;T&gt; <i>is</i> false</del>
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<del><i>error-variant</i> <i>errors</i>; // <i>exposition only</i></del>
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};
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}
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</pre>
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</blockquote>
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</p>
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<p>
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The definition of <code><i>error-variant</i></code> isn't needed, i.e., remove <sref ref="[task.promise]"/> paragraph 2:
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<blockquote>
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<p><del>
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-2- <code><i>error-variant</i></code> is a <code>variant&lt;monostate, remove_cvref_t&lt;E&gt;...&gt;</code>, with duplicate types removed, where <code>E...</code> are template arguments of the specialization of <code>execution::completion_signatures</code> denoted by <code>error_types</code>.
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</del></p>
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</blockquote>
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</p>
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<p>
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In <sref ref="[task.promise]"/> change paragraph 7 to use the members added to <code><i>state</i></code>:
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<blockquote>
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<pre>auto final_suspend() noexcept</pre>
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<p>-7- <i>Returns</i>: An awaitable object of unspecified type (<sref ref="[expr.await]"/>) whose member functions arrange for the completion of the asynchronous operation associated with <code><i>STATE</i>(*this)</code><del> by invoking</del><ins>. Let <code>st</code> be a reference to <code><i>STATE</i>(*this)</code>. The asynchronous completion first destroys the coroutine frame using <code>st.<i>handle</i>.destroy()</code> and then invokes</ins>:</p>
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<ul>
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<li>-7.1- <code>set_error(std::move(<del><i>RCVR</i>(*this)</del><ins>st.<i>rcvr</i></ins>), std::move(<del>e</del><ins>st.<i>error</i></ins>))</code> if <del><code><i>errors</i>.index()</code> is greater than zero and <code>e</code> is the value held by <code><i>errors</i></code></del><ins><code>bool(st.<i>error</i>)</code> is <code>true</code></ins>, otherwise</li>
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<li>-7.2- <code>set_value(std::move(<del><i>RCVR</i>(*this)</del><ins>st.<i>rcvr</i></ins>))</code> if <code>is_void&lt;T&gt;</code> is <code>true</code>, and otherwise</li>
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<li>-7.3- <code>set_value(std::move(<del><i>RCVR</i>(*this)</del><ins>st.<i>rcvr</i></ins>), *<ins>st.</ins><i>result</i>)</code>.</li>
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</ul>
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</blockquote>
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</p>
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<p>
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Change the specification of <code>yield_value</code> to destroy the coroutine frame before invoking the <code>set_error</code> completion, i.e., change <sref ref="[task.promise]"/> paragraph 9:
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<blockquote>
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<p>-9- <i>Returns</i>: An awaitable object of unspecified type ([expr.await]) whose member functions arrange for the calling coroutine to be suspended and then completes the asynchronous operation associated with <code><i>STATE</i>(*this)</code><del> by</del><ins>. Let <code>st</code> be a reference to <code><i>STATE</i>(*this)</code>. Then the asynchronous operation completes by first destroying the coroutine frame using <code>st.<i>handle</i>.destroy()</code> and then</ins> invoking <code>set_error(std::move(<del><i>RCVR</i>(*this)</del><ins>st.<i>rcvr</i></ins>), Cerr(std::move(err.error)))</code>.
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</p>
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</blockquote>
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</p>
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<p>
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Change the specification of <code>unhandled_stopped</code> to destroy the coroutine frame before invoking the <code>set_stopped</code> completion, i.e., change <sref ref="[task.promise]"/> paragraph 13:
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<blockquote>
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<pre>coroutine_handle&lt;&gt; unhandled_stopped();</pre>
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<p>-13- <i>Effects</i>: Completes the asynchronous operation associated with <code><i>STATE</i>(*this)</code><del> by</del><ins>. Let <code>st</code> be a reference to <code><i>STATE</i>(*this)</code>. The asynchronous operation is completed by first destroying the coroutine frame using <code>st.<i>handle</i>.destroy()</code> and then</ins> invoking <code>set_stopped(std::move(<del><i>RCVR</i>(*this)</del><ins>st.<i>rcvr</i></ins>))</code>.</p>
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</blockquote>
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</p>
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</resolution>
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