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<div class="identifier-type">customization point object</div><div class="header"><execution></div><h1 itemprop="name"><span class="namespace" title="namespace std::this_thread">std::this_thread::</span><span class="token">sync_wait</span><span class="cpp cpp26" title="C++26で追加">(C++26)</span></h1>
<div itemprop="articleBody"><p><div class="codehilite"><pre><span></span><code><span class="k">namespace</span><span class="w"> </span><span class="nn">std</span><span class="o">::</span><span class="nn">this_thread</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">sync_wait_t</span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="n"><i>unspecified</i></span><span class="w"> </span><span class="p">};</span>
<span class="w"> </span><span class="kr">inline</span><span class="w"> </span><span class="k">constexpr</span><span class="w"> </span><span class="n">sync_wait_t</span><span class="w"> </span><span class="n">sync_wait</span><span class="p">{};</span>
<span class="p">}</span>
</code></pre></div>
</p>
<h2>概要</h2>
<p><code>sync_wait</code>は、入力<a href="../execution/sender.html">Sender</a>が完了するまで現在のスレッドをブロックし、非<a class="cpprefjp-defined-word" data-desc="マルチスレッド実行時にリソースの所有権に基づいて実行順序を制御する操作">同期操作</a>の結果を取得するSenderコンシューマである。</p>
<p><code>sync_wait</code>は入力Senderが<a href="../execution/set_value.html">値完了シグネチャ</a>を1個だけ持つことを要求する。
値完了シグネチャが複数存在する場合は<code><a href="sync_wait_with_variant.html">sync_wait_with_variant</a></code>アルゴリズムを利用する。</p>
<p>入力Senderの値完了シグネチャが<code><a href="../execution/set_value.html">set_value_t</a>(Ts...)</code>のとき、<code>sync_wait</code>の結果型は<code><a href="../../optional/optional.html">optional</a><<a href="../../tuple/tuple.html">tuple</a><Ts...>></code>となる。</p>
<h2>効果</h2>
<p>説明用の<code>sndr</code>を<code>decltype((sndr))</code>が<code>Sndr</code>型となる式とする。</p>
<p>呼び出し式<code>this_thread::sync_wait(sndr)</code>は<code>sndr</code>が1回だけ評価されることを除いて、下記と等価。</p>
<p><div class="codehilite"><pre><span></span><code><span class="n"><a href="../execution/apply_sender.html">apply_sender</a></span><span class="p">(</span><span class="n"><a href="../execution/get-domain-early.html">get-domain-early</a></span><span class="p">(</span><span class="n">sndr</span><span class="p">),</span><span class="w"> </span><span class="n">sync_wait</span><span class="p">,</span><span class="w"> </span><span class="n">sndr</span><span class="p">)</span>
</code></pre></div>
</p>
<ul>
<li><code><a href="../execution/sender_in.html">sender_in</a><Sndr, <a href="sync-wait-env.html">sync-wait-env</a>> == true</code>であること。</li>
<li>型<code>sync-wait-result-type<Sndr></code>が<a class="cpprefjp-defined-word" data-desc="プログラムが文法規則・診断対象の意味規則・単一定義規則を満たすこと" href="../../../implementation-compliance.html#dfn-well-formed">適格</a>であること。</li>
<li>上記の<code>apply_sender</code>式を<code>e</code>としたとき、<code><a href="../../concepts/same_as.html">same_as</a><decltype(e), sync-wait-result-type<Sndr>> == true</code>であること。</li>
</ul>
<h3>結果型</h3>
<p><code>sync_wait</code>の結果型となる、説明専用のエイリアステンプレート<code>sync-wait-result-type</code>を下記の通り定義する。</p>
<p><div class="codehilite"><pre><span></span><code><span class="k">namespace</span><span class="w"> </span><span class="nn">std</span><span class="o">::</span><span class="nn">this_thread</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">template</span><span class="o"><</span><span class="n"><a href="../execution/sender_in.html">execution::sender_in</a></span><span class="o"><</span><span class="n"><a href="sync-wait-env.html">sync-wait-env</a></span><span class="o">></span><span class="w"> </span><span class="n">Sndr</span><span class="o">></span>
<span class="w"> </span><span class="k">using</span><span class="w"> </span><span class="n">sync</span><span class="o">-</span><span class="n">wait</span><span class="o">-</span><span class="n">result</span><span class="o">-</span><span class="n">type</span><span class="w"> </span><span class="o">=</span>
<span class="w"> </span><span class="n"><a href="../../optional/optional.html">optional</a></span><span class="o"><</span><span class="n"><a href="../execution/value_types_of_t.html">execution::value_types_of_t</a></span><span class="o"><</span><span class="n">Sndr</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="sync-wait-env.html">sync-wait-env</a></span><span class="p">,</span>
<span class="w"> </span><span class="n"><a href="../execution/decayed-tuple.html">decayed-tuple</a></span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../../type_traits/type_identity.html">type_identity_t</a></span><span class="o">>></span><span class="p">;</span>
<span class="p">}</span>
</code></pre></div>
</p>
<h3>Senderアルゴリズムタグ <code>sync_wait</code></h3>
<p>説明用の<code>sndr</code>を<code>decltype((sndr))</code>が<code>Sndr</code>型となる式とする。</p>
<p><code><a href="../execution/sender_to.html">sender_to</a><Sndr, <a href="sync-wait-receiver.html">sync-wait-receiver</a><Sndr>> == false</code>のとき、式<code>sync_wait.apply_sender(sndr)</code>は<a class="cpprefjp-defined-word" data-desc="プログラムが適格でないこと。コンパイルエラーなどになる" href="../../../implementation-compliance.html#dfn-ill-formed">不適格</a>となる。</p>
<p>そうでなければ、式<code>sync_wait.apply_sender(sndr)</code>は下記と等価。</p>
<p><div class="codehilite"><pre><span></span><code><span class="n"><a href="sync-wait-receiver.html">sync-wait-state</a></span><span class="o"><</span><span class="n">Sndr</span><span class="o">></span><span class="w"> </span><span class="n">state</span><span class="p">;</span>
<span class="k">auto</span><span class="w"> </span><span class="n">op</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><a href="../execution/connect.html">connect</a></span><span class="p">(</span><span class="n">sndr</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="sync-wait-receiver.html">sync-wait-receiver</a></span><span class="o"><</span><span class="n">Sndr</span><span class="o">></span><span class="p">{</span><span class="o">&</span><span class="n">state</span><span class="p">});</span>
<span class="n"><a href="../execution/start.html">start</a></span><span class="p">(</span><span class="n">op</span><span class="p">);</span>
<span class="n">state</span><span class="p">.</span><span class="n"><a href="../execution/run_loop/run.html">loop.run()</a></span><span class="p">;</span>
<span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">state</span><span class="p">.</span><span class="n">error</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n"><a href="../../exception/rethrow_exception.html">rethrow_exception</a></span><span class="p">(</span><span class="n"><a href="../../utility/move.html">std::move</a></span><span class="p">(</span><span class="n">state</span><span class="p">.</span><span class="n">error</span><span class="p">));</span>
<span class="p">}</span>
<span class="k">return</span><span class="w"> </span><span class="n"><a href="../../utility/move.html">std::move</a></span><span class="p">(</span><span class="n">state</span><span class="p">.</span><span class="n">result</span><span class="p">);</span>
</code></pre></div>
</p>
<h2>カスタマイゼーションポイント</h2>
<p>入力<a href="../execution/sender.html">Sender</a><code>sndr</code>に<a href="../execution/get-domain-early.html">関連付けられた実行ドメイン</a><code>dom</code>に対して、
<code><a href="../execution/apply_sender.html">execution::apply_sender</a></code>経由で<code>dom.apply_sender(sync_wait, sndr)</code>が呼ばれる。</p>
<p><a href="../execution/default_domain.html">デフォルト実行ドメイン</a>では、<code>sync_wait.apply_sender(sndr)</code>が呼ばれる。</p>
<p>下記を満たさない場合、呼び出し式<code>this_thread::sync_wait(sndr)</code>の<a class="cpprefjp-defined-word" data-desc="未定義の動作。処理系は予期せぬ動作をする可能性がある。要するに動作保証対象外。undefined behavior (UB)。" href="../../../implementation-compliance.html#dfn-undefined-behavior">動作は未定義</a>となる。</p>
<ul>
<li>指定したSenderが完了するまで、前方進行保証委任(forward progress guarantee delegation)による現在のスレッドをブロックすること。</li>
<li>指定したSenderの非<a class="cpprefjp-defined-word" data-desc="マルチスレッド実行時にリソースの所有権に基づいて実行順序を制御する操作">同期操作</a>の結果が返る場合<ul>
<li><a href="../execution/set_value.html">値完了</a>の場合、結果データは<code><a href="../../optional/optional.html">optional</a></code>オブジェクト内の<code><a href="../../tuple/tuple.html">tuple</a></code>で返されること。</li>
<li><a href="../execution/set_error.html">エラー完了</a>の場合、<a class="cpprefjp-defined-word" data-desc="問題が発生したときに、現在実行位置を過去に通過・記録した位置に戻し、文脈情報を添えて紐づけられた処理(例外ハンドラー)を呼び出す仕組み。またはその事態">例外</a>を送出すること。</li>
<li><a href="../execution/set_stopped.html">停止完了</a>の場合、無効値<code><a href="../../optional/optional.html">optional</a></code>オブジェクトが返されること。</li>
</ul>
</li>
</ul>
<h2>例</h2>
<p><div class="codehilite"><pre><span></span><code><span class="cp">#include <a href="../../print.html"><print></a></span>
<span class="cp">#include <a href="../../execution.html"><execution></a></span>
<span class="k">namespace</span><span class="w"> </span><span class="nn">ex</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nn">std</span><span class="o">::</span><span class="nn">execution</span><span class="p">;</span>
<span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p">()</span>
<span class="p">{</span>
<span class="w"> </span><span class="c1">// 値(100, 'X')を送信するSender</span>
<span class="w"> </span><span class="n"><a href="../execution/sender.html">ex::sender</a></span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">sndr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><a href="../execution/just.html">ex::just</a></span><span class="p">(</span><span class="mi">100</span><span class="p">,</span><span class="w"> </span><span class="sc">'X'</span><span class="p">);</span>
<span class="w"> </span><span class="c1">// メインスレッド上で完了待機</span>
<span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><span style="color:#ff0000">std::this_thread::sync_wait</span></span><span class="p">(</span><span class="n">sndr</span><span class="p">);</span>
<span class="w"> </span><span class="c1">// 結果型optional<<a href="../../tuple/tuple.html">tuple</a><int,char>>から値を取り出す</span>
<span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="p">[</span><span class="n">n</span><span class="p">,</span><span class="w"> </span><span class="n">c</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">result</span><span class="p">.</span><span class="n"><a href="../../optional/optional/value.html">value()</a></span><span class="p">;</span>
<span class="w"> </span><span class="n"><a href="../../print/println.html">std::println</a></span><span class="p">(</span><span class="s">"result=({}, {})"</span><span class="p">,</span><span class="w"> </span><span class="n">n</span><span class="p">,</span><span class="w"> </span><span class="n">c</span><span class="p">);</span>
<span class="p">}</span>
</code></pre></div>
</p>
<h3>出力</h3>
<p><pre><code>result=(100, X)
</code></pre></p>
<h2>バージョン</h2>
<h3>言語</h3>
<ul>
<li>C++26</li>
</ul>
<h3>処理系</h3>
<ul>
<li><a href="../../../implementation.html#clang">Clang</a>: ??</li>
<li><a href="../../../implementation.html#gcc">GCC</a>: ??</li>
<li><a href="../../../implementation.html#icc">ICC</a>: ??</li>
<li><a href="../../../implementation.html#visual_cpp">Visual C++</a>: ??</li>
</ul>
<h2>関連項目</h2>
<ul>
<li><code><a href="../execution/sender.html">execution::sender</a></code></li>
<li><code><a href="sync_wait_with_variant.html">this_thread::sync_wait_with_variant</a></code></li>
</ul>
<h2>参照</h2>
<ul>
<li><a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p2300r10.html" target="_blank">P2300R10 <code>std::execution</code></a></li>
<li><a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2025/p3557r3.html" target="_blank">P3557R3 High-Quality Sender Diagnostics with Constexpr Exceptions</a></li>
</ul></div>
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