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<title>co_spawn (6 of 6 overloads)</title>
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<table cellpadding="2" width="100%"><tr><td valign="top"><img alt="asio C++ library" width="250" height="60" src="../../../asio.png"></td></tr></table>
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<div class="titlepage"><div><div><h4 class="title">
<a name="asio.reference.co_spawn.overload6"></a><a class="link" href="overload6.html" title="co_spawn (6 of 6 overloads)">co_spawn (6 of 6
overloads)</a>
</h4></div></div></div>
<p>
Spawn a new coroutined-based thread of execution.
</p>
<pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span>
<span class="keyword">typename</span> <span class="identifier">ExecutionContext</span><span class="special">,</span>
<span class="keyword">typename</span> <span class="identifier">F</span><span class="special">,</span>
<span class="keyword">typename</span> <span class="identifier">CompletionToken</span> <span class="special">=</span> <a class="link" href="../asynchronous_operations.html#asio.reference.asynchronous_operations.default_completion_tokens"><span class="emphasis"><em>DEFAULT</em></span></a><span class="special">&gt;</span>
<a class="link" href="../asynchronous_operations.html#asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type"><span class="emphasis"><em>DEDUCED</em></span></a> <span class="identifier">co_spawn</span><span class="special">(</span>
<span class="identifier">ExecutionContext</span> <span class="special">&amp;</span> <span class="identifier">ctx</span><span class="special">,</span>
<span class="identifier">F</span> <span class="special">&amp;&amp;</span> <span class="identifier">f</span><span class="special">,</span>
<span class="identifier">CompletionToken</span> <span class="special">&amp;&amp;</span> <span class="identifier">token</span> <span class="special">=</span> <a class="link" href="../asynchronous_operations.html#asio.reference.asynchronous_operations.default_completion_tokens"><span class="emphasis"><em>DEFAULT</em></span></a><span class="special">,</span>
<span class="keyword">typename</span> <span class="identifier">constraint</span><span class="special">&lt;</span> <span class="identifier">is_convertible</span><span class="special">&lt;</span> <span class="identifier">ExecutionContext</span> <span class="special">&amp;,</span> <span class="identifier">execution_context</span> <span class="special">&amp;</span> <span class="special">&gt;::</span><span class="identifier">value</span> <span class="special">&gt;::</span><span class="identifier">type</span> <span class="special">=</span> <span class="number">0</span><span class="special">);</span>
</pre>
<h6>
<a name="asio.reference.co_spawn.overload6.h0"></a>
<span><a name="asio.reference.co_spawn.overload6.parameters"></a></span><a class="link" href="overload6.html#asio.reference.co_spawn.overload6.parameters">Parameters</a>
</h6>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term">ctx</span></dt>
<dd><p>
An execution context that will provide the executor to be used to
schedule the new thread of execution.
</p></dd>
<dt><span class="term">f</span></dt>
<dd><p>
A nullary function object with a return type of the form <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">awaitable</span><span class="special">&lt;</span><span class="identifier">R</span><span class="special">,</span><span class="identifier">E</span><span class="special">&gt;</span></code>
that will be used as the coroutine's entry point.
</p></dd>
<dt><span class="term">token</span></dt>
<dd><p>
The <a class="link" href="../../overview/model/completion_tokens.html" title="Completion Tokens">completion
token</a> that will handle the notification that the thread of
execution has completed. If <code class="computeroutput"><span class="identifier">R</span></code>
is <code class="computeroutput"><span class="keyword">void</span></code>, the function
signature of the completion handler must be:
</p></dd>
</dl>
</div>
<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">handler</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">exception_ptr</span><span class="special">);</span>
</pre>
<p>
Otherwise, the function signature of the completion handler must be:
</p>
<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">handler</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">exception_ptr</span><span class="special">,</span> <span class="identifier">R</span><span class="special">);</span>
</pre>
<h6>
<a name="asio.reference.co_spawn.overload6.h1"></a>
<span><a name="asio.reference.co_spawn.overload6.completion_signature"></a></span><a class="link" href="overload6.html#asio.reference.co_spawn.overload6.completion_signature">Completion
Signature</a>
</h6>
<pre class="programlisting"><span class="keyword">void</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">exception_ptr</span><span class="special">,</span> <span class="identifier">R</span><span class="special">)</span>
</pre>
<p>
where <code class="computeroutput"><span class="identifier">R</span></code> is the first template
argument to the <code class="computeroutput"><span class="identifier">awaitable</span></code>
returned by the supplied function object <code class="computeroutput"><span class="identifier">F</span><span class="special">:</span></code>
</p>
<pre class="programlisting"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">awaitable</span><span class="special">&lt;</span><span class="identifier">R</span><span class="special">,</span> <span class="identifier">AwaitableExecutor</span><span class="special">&gt;</span> <span class="identifier">F</span><span class="special">()</span>
</pre>
<h6>
<a name="asio.reference.co_spawn.overload6.h2"></a>
<span><a name="asio.reference.co_spawn.overload6.example"></a></span><a class="link" href="overload6.html#asio.reference.co_spawn.overload6.example">Example</a>
</h6>
<pre class="programlisting"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">awaitable</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">&gt;</span> <span class="identifier">echo</span><span class="special">(</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span> <span class="identifier">socket</span><span class="special">)</span>
<span class="special">{</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">bytes_transferred</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
<span class="keyword">try</span>
<span class="special">{</span>
<span class="keyword">char</span> <span class="identifier">data</span><span class="special">[</span><span class="number">1024</span><span class="special">];</span>
<span class="keyword">for</span> <span class="special">(;;)</span>
<span class="special">{</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">n</span> <span class="special">=</span> <span class="identifier">co_await</span> <span class="identifier">socket</span><span class="special">.</span><span class="identifier">async_read_some</span><span class="special">(</span>
<span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">(</span><span class="identifier">data</span><span class="special">),</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">use_awaitable</span><span class="special">);</span>
<span class="identifier">co_await</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">async_write</span><span class="special">(</span><span class="identifier">socket</span><span class="special">,</span>
<span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">(</span><span class="identifier">data</span><span class="special">,</span> <span class="identifier">n</span><span class="special">),</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">use_awaitable</span><span class="special">);</span>
<span class="identifier">bytes_transferred</span> <span class="special">+=</span> <span class="identifier">n</span><span class="special">;</span>
<span class="special">}</span>
<span class="special">}</span>
<span class="keyword">catch</span> <span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">exception</span><span class="special">&amp;)</span>
<span class="special">{</span>
<span class="special">}</span>
<span class="identifier">co_return</span> <span class="identifier">bytes_transferred</span><span class="special">;</span>
<span class="special">}</span>
<span class="comment">// ...</span>
<span class="identifier">asio</span><span class="special">::</span><span class="identifier">co_spawn</span><span class="special">(</span><span class="identifier">my_io_context</span><span class="special">,</span>
<span class="special">[</span><span class="identifier">socket</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">my_tcp_socket</span><span class="special">)]()</span> <span class="keyword">mutable</span>
<span class="special">-&gt;</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">awaitable</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span>
<span class="special">{</span>
<span class="keyword">try</span>
<span class="special">{</span>
<span class="keyword">char</span> <span class="identifier">data</span><span class="special">[</span><span class="number">1024</span><span class="special">];</span>
<span class="keyword">for</span> <span class="special">(;;)</span>
<span class="special">{</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">n</span> <span class="special">=</span> <span class="identifier">co_await</span> <span class="identifier">socket</span><span class="special">.</span><span class="identifier">async_read_some</span><span class="special">(</span>
<span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">(</span><span class="identifier">data</span><span class="special">),</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">use_awaitable</span><span class="special">);</span>
<span class="identifier">co_await</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">async_write</span><span class="special">(</span><span class="identifier">socket</span><span class="special">,</span>
<span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">(</span><span class="identifier">data</span><span class="special">,</span> <span class="identifier">n</span><span class="special">),</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">use_awaitable</span><span class="special">);</span>
<span class="special">}</span>
<span class="special">}</span>
<span class="keyword">catch</span> <span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">exception</span><span class="special">&amp;</span> <span class="identifier">e</span><span class="special">)</span>
<span class="special">{</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">cerr</span> <span class="special">&lt;&lt;</span> <span class="string">"Exception: "</span> <span class="special">&lt;&lt;</span> <span class="identifier">e</span><span class="special">.</span><span class="identifier">what</span><span class="special">()</span> <span class="special">&lt;&lt;</span> <span class="string">"\n"</span><span class="special">;</span>
<span class="special">}</span>
<span class="special">},</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">detached</span><span class="special">);</span>
</pre>
<h6>
<a name="asio.reference.co_spawn.overload6.h3"></a>
<span><a name="asio.reference.co_spawn.overload6.per_operation_cancellation"></a></span><a class="link" href="overload6.html#asio.reference.co_spawn.overload6.per_operation_cancellation">Per-Operation
Cancellation</a>
</h6>
<p>
The new thread of execution is created with a cancellation state that supports
<code class="computeroutput"><span class="identifier">cancellation_type</span><span class="special">::</span><span class="identifier">terminal</span></code> values only. To change the cancellation
state, call <a class="link" href="../this_coro__reset_cancellation_state.html" title="this_coro::reset_cancellation_state"><code class="computeroutput"><span class="identifier">this_coro</span><span class="special">::</span><span class="identifier">reset_cancellation_state</span></code></a>.
</p>
</div>
<div class="copyright-footer">Copyright © 2003-2023 Christopher M. Kohlhoff<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
</p>
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