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<title>defer (2 of 3 overloads)</title>
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<div class="titlepage"><div><div><h4 class="title">
<a name="asio.reference.defer.overload2"></a><a class="link" href="overload2.html" title="defer (2 of 3 overloads)">defer (2 of 3 overloads)</a>
</h4></div></div></div>
<p>
Submits a completion token or function object for execution.
</p>
<pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span>
<span class="keyword">typename</span> <a class="link" href="../Executor1.html" title="Executor requirements">Executor</a><span class="special">,</span>
<span class="keyword">typename</span> <a class="link" href="../NullaryToken.html" title="Nullary token requirements">NullaryToken</a> <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">defer</span><span class="special">(</span>
<span class="keyword">const</span> <span class="identifier">Executor</span> <span class="special">&amp;</span> <span class="identifier">ex</span><span class="special">,</span>
<span class="identifier">NullaryToken</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="special">(</span><span class="identifier">execution</span><span class="special">::</span><span class="identifier">is_executor</span><span class="special">&lt;</span> <span class="identifier">Executor</span> <span class="special">&gt;::</span><span class="identifier">value</span> <span class="special">&amp;&amp;</span><span class="identifier">can_require</span><span class="special">&lt;</span> <span class="identifier">Executor</span><span class="special">,</span> <span class="identifier">execution</span><span class="special">::</span><span class="identifier">blocking_t</span><span class="special">::</span><span class="identifier">never_t</span> <span class="special">&gt;::</span><span class="identifier">value</span><span class="special">)||</span><span class="identifier">is_executor</span><span class="special">&lt;</span> <span class="identifier">Executor</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>
<p>
This function submits an object for execution using the specified executor.
The function object is queued for execution, and is never called from the
current thread prior to returning from <code class="computeroutput"><span class="identifier">defer</span><span class="special">()</span></code>.
</p>
<p>
The use of <code class="computeroutput"><span class="identifier">defer</span><span class="special">()</span></code>,
rather than <a class="link" href="../post.html" title="post"><code class="computeroutput"><span class="identifier">post</span></code></a>,
indicates the caller's preference that the executor defer the queueing
of the function object. This may allow the executor to optimise queueing
for cases when the function object represents a continuation of the current
call context.
</p>
<h6>
<a name="asio.reference.defer.overload2.h0"></a>
<span><a name="asio.reference.defer.overload2.parameters"></a></span><a class="link" href="overload2.html#asio.reference.defer.overload2.parameters">Parameters</a>
</h6>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term">ex</span></dt>
<dd><p>
The target executor.
</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 be used to produce a completion handler. 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>
</pre>
</dd>
</dl>
</div>
<h6>
<a name="asio.reference.defer.overload2.h1"></a>
<span><a name="asio.reference.defer.overload2.return_value"></a></span><a class="link" href="overload2.html#asio.reference.defer.overload2.return_value">Return
Value</a>
</h6>
<p>
This function returns <code class="computeroutput"><span class="identifier">async_initiate</span><span class="special">&lt;</span><span class="identifier">NullaryToken</span><span class="special">,</span> <span class="keyword">void</span><span class="special">()&gt;(</span><span class="identifier">Init</span><span class="special">{</span><span class="identifier">ex</span><span class="special">},</span> <span class="identifier">token</span><span class="special">)</span></code>,
where <code class="computeroutput"><span class="identifier">Init</span></code> is a function
object type defined as:
</p>
<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">Init</span>
<span class="special">{</span>
<span class="keyword">public</span><span class="special">:</span>
<span class="keyword">using</span> <span class="identifier">executor_type</span> <span class="special">=</span> <span class="identifier">Executor</span><span class="special">;</span>
<span class="keyword">explicit</span> <span class="identifier">Init</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">Executor</span><span class="special">&amp;</span> <span class="identifier">ex</span><span class="special">)</span> <span class="special">:</span> <span class="identifier">ex_</span><span class="special">(</span><span class="identifier">ex</span><span class="special">)</span> <span class="special">{}</span>
<span class="identifier">executor_type</span> <span class="identifier">get_executor</span><span class="special">()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span> <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">ex_</span><span class="special">;</span> <span class="special">}</span>
<span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">CompletionHandler</span><span class="special">&gt;</span>
<span class="keyword">void</span> <span class="keyword">operator</span><span class="special">()(</span><span class="identifier">CompletionHandler</span><span class="special">&amp;&amp;</span> <span class="identifier">completion_handler</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
<span class="keyword">private</span><span class="special">:</span>
<span class="identifier">Executor</span> <span class="identifier">ex_</span><span class="special">;</span> <span class="comment">// exposition only</span>
<span class="special">};</span>
</pre>
<p>
The function call operator of <code class="computeroutput"><span class="identifier">Init</span><span class="special">:</span></code>
</p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
<p class="simpara">
Obtains the handler's associated executor object <code class="computeroutput"><span class="identifier">ex1</span></code>
of type <code class="computeroutput"><span class="identifier">Ex1</span></code> by performing
</p>
<pre class="programlisting"><span class="keyword">auto</span> <span class="identifier">ex1</span> <span class="special">=</span> <span class="identifier">get_associated_executor</span><span class="special">(</span><span class="identifier">handler</span><span class="special">,</span> <span class="identifier">ex</span><span class="special">);</span>
</pre>
</li>
<li class="listitem">
<p class="simpara">
Obtains the handler's associated allocator object <code class="computeroutput"><span class="identifier">alloc</span></code>
by performing
</p>
<pre class="programlisting"><span class="keyword">auto</span> <span class="identifier">alloc</span> <span class="special">=</span> <span class="identifier">get_associated_allocator</span><span class="special">(</span><span class="identifier">handler</span><span class="special">);</span>
</pre>
</li>
<li class="listitem">
<p class="simpara">
If <code class="computeroutput"><span class="identifier">execution</span><span class="special">::</span><span class="identifier">is_executor</span><span class="special">&lt;</span><span class="identifier">Ex1</span><span class="special">&gt;::</span><span class="identifier">value</span></code> is true, constructs a function
object <code class="computeroutput"><span class="identifier">f</span></code> with a member
<code class="computeroutput"><span class="identifier">executor_</span></code> that is initialised
with <code class="computeroutput"><span class="identifier">prefer</span><span class="special">(</span><span class="identifier">ex1</span><span class="special">,</span> <span class="identifier">execution</span><span class="special">::</span><span class="identifier">outstanding_work</span><span class="special">.</span><span class="identifier">tracked</span><span class="special">)</span></code>,
a member <code class="computeroutput"><span class="identifier">handler_</span></code> that
is a decay-copy of <code class="computeroutput"><span class="identifier">completion_handler</span></code>,
and a function call operator that performs:
</p>
<pre class="programlisting"><span class="keyword">auto</span> <span class="identifier">a</span> <span class="special">=</span> <span class="identifier">get_associated_allocator</span><span class="special">(</span><span class="identifier">handler_</span><span class="special">);</span>
<span class="identifier">prefer</span><span class="special">(</span><span class="identifier">executor_</span><span class="special">,</span> <span class="identifier">execution</span><span class="special">::</span><span class="identifier">allocator</span><span class="special">(</span><span class="identifier">a</span><span class="special">)).</span><span class="identifier">execute</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">handler_</span><span class="special">));</span>
</pre>
</li>
<li class="listitem">
<p class="simpara">
If <code class="computeroutput"><span class="identifier">execution</span><span class="special">::</span><span class="identifier">is_executor</span><span class="special">&lt;</span><span class="identifier">Ex1</span><span class="special">&gt;::</span><span class="identifier">value</span></code> is false, constructs a function
object <code class="computeroutput"><span class="identifier">f</span></code> with a member
<code class="computeroutput"><span class="identifier">work_</span></code> that is initialised
with <code class="computeroutput"><span class="identifier">make_work_guard</span><span class="special">(</span><span class="identifier">ex1</span><span class="special">)</span></code>, a member <code class="computeroutput"><span class="identifier">handler_</span></code>
that is a decay-copy of <code class="computeroutput"><span class="identifier">completion_handler</span></code>,
and a function call operator that performs:
</p>
<pre class="programlisting"><span class="keyword">auto</span> <span class="identifier">a</span> <span class="special">=</span> <span class="identifier">get_associated_allocator</span><span class="special">(</span><span class="identifier">handler_</span><span class="special">);</span>
<span class="identifier">work_</span><span class="special">.</span><span class="identifier">get_executor</span><span class="special">().</span><span class="identifier">dispatch</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">handler_</span><span class="special">),</span> <span class="identifier">a</span><span class="special">);</span>
<span class="identifier">work_</span><span class="special">.</span><span class="identifier">reset</span><span class="special">();</span>
</pre>
</li>
<li class="listitem">
<p class="simpara">
If <code class="computeroutput"><span class="identifier">execution</span><span class="special">::</span><span class="identifier">is_executor</span><span class="special">&lt;</span><span class="identifier">Ex</span><span class="special">&gt;::</span><span class="identifier">value</span></code> is true, performs
</p>
<pre class="programlisting"><span class="identifier">prefer</span><span class="special">(</span>
<span class="identifier">require</span><span class="special">(</span><span class="identifier">ex</span><span class="special">,</span> <span class="identifier">execution</span><span class="special">::</span><span class="identifier">blocking</span><span class="special">.</span><span class="identifier">never</span><span class="special">),</span>
<span class="identifier">execution</span><span class="special">::</span><span class="identifier">relationship</span><span class="special">.</span><span class="identifier">continuation</span><span class="special">,</span>
<span class="identifier">execution</span><span class="special">::</span><span class="identifier">allocator</span><span class="special">(</span><span class="identifier">alloc</span><span class="special">)</span>
<span class="special">).</span><span class="identifier">execute</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">f</span><span class="special">));</span>
</pre>
</li>
<li class="listitem">
<p class="simpara">
If <code class="computeroutput"><span class="identifier">execution</span><span class="special">::</span><span class="identifier">is_executor</span><span class="special">&lt;</span><span class="identifier">Ex</span><span class="special">&gt;::</span><span class="identifier">value</span></code> is false, performs
</p>
<pre class="programlisting"><span class="identifier">ex</span><span class="special">.</span><span class="identifier">defer</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">f</span><span class="special">),</span> <span class="identifier">alloc</span><span class="special">);</span>
</pre>
</li>
</ul></div>
<h6>
<a name="asio.reference.defer.overload2.h2"></a>
<span><a name="asio.reference.defer.overload2.completion_signature"></a></span><a class="link" href="overload2.html#asio.reference.defer.overload2.completion_signature">Completion
Signature</a>
</h6>
<pre class="programlisting"><span class="keyword">void</span><span class="special">()</span>
</pre>
</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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