115 lines
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115 lines
8.2 KiB
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<title>asio_handler_invoke</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="section">
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<div class="titlepage"><div><div><h3 class="title">
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<a name="asio.reference.asio_handler_invoke"></a><a class="link" href="asio_handler_invoke.html" title="asio_handler_invoke">asio_handler_invoke</a>
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</h3></div></div></div>
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<p>
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<a class="indexterm" name="asio.indexterm.asio_handler_invoke"></a>
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</p>
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<p>
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(Deprecated: Use the <a class="link" href="associated_executor.html" title="associated_executor"><code class="computeroutput"><span class="identifier">associated_executor</span></code></a> trait.) Default
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invoke function for handlers.
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</p>
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<p>
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Default handler invocation hook used for non-const function objects.
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</p>
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<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span>
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<span class="keyword">typename</span> <span class="identifier">Function</span><span class="special">></span>
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<span class="identifier">asio_handler_invoke_is_deprecated</span> <a class="link" href="asio_handler_invoke/overload1.html" title="asio_handler_invoke (1 of 2 overloads)">asio_handler_invoke</a><span class="special">(</span>
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<span class="identifier">Function</span> <span class="special">&</span> <span class="identifier">function</span><span class="special">,</span>
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<span class="special">...</span> <span class="special">);</span>
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<span class="emphasis"><em>» <a class="link" href="asio_handler_invoke/overload1.html" title="asio_handler_invoke (1 of 2 overloads)">more...</a></em></span>
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</pre>
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<p>
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Default handler invocation hook used for const function objects.
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</p>
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<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span>
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<span class="keyword">typename</span> <span class="identifier">Function</span><span class="special">></span>
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<span class="identifier">asio_handler_invoke_is_deprecated</span> <a class="link" href="asio_handler_invoke/overload2.html" title="asio_handler_invoke (2 of 2 overloads)">asio_handler_invoke</a><span class="special">(</span>
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<span class="keyword">const</span> <span class="identifier">Function</span> <span class="special">&</span> <span class="identifier">function</span><span class="special">,</span>
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<span class="special">...</span> <span class="special">);</span>
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<span class="emphasis"><em>» <a class="link" href="asio_handler_invoke/overload2.html" title="asio_handler_invoke (2 of 2 overloads)">more...</a></em></span>
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</pre>
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<p>
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Completion handlers for asynchronous operations are invoked by the <a class="link" href="io_context.html" title="io_context"><code class="computeroutput"><span class="identifier">io_context</span></code></a>
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associated with the corresponding object (e.g. a socket or deadline_timer).
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Certain guarantees are made on when the handler may be invoked, in particular
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that a handler can only be invoked from a thread that is currently calling
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<code class="computeroutput"><span class="identifier">run</span><span class="special">()</span></code>
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on the corresponding <a class="link" href="io_context.html" title="io_context"><code class="computeroutput"><span class="identifier">io_context</span></code></a> object. Handlers may
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subsequently be invoked through other objects (such as <a class="link" href="io_context__strand.html" title="io_context::strand"><code class="computeroutput"><span class="identifier">io_context</span><span class="special">::</span><span class="identifier">strand</span></code></a> objects) that provide additional
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guarantees.
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</p>
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<p>
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When asynchronous operations are composed from other asynchronous operations,
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all intermediate handlers should be invoked using the same method as the
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final handler. This is required to ensure that user-defined objects are not
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accessed in a way that may violate the guarantees. This hooking function
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ensures that the invoked method used for the final handler is accessible
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at each intermediate step.
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</p>
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<p>
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Implement asio_handler_invoke for your own handlers to specify a custom invocation
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strategy.
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</p>
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<p>
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This default implementation invokes the function object like so:
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</p>
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<pre class="programlisting"><span class="identifier">function</span><span class="special">();</span>
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</pre>
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<p>
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If necessary, the default implementation makes a copy of the function object
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so that the non-const operator() can be used.
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</p>
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<h5>
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<a name="asio.reference.asio_handler_invoke.h0"></a>
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<span><a name="asio.reference.asio_handler_invoke.example"></a></span><a class="link" href="asio_handler_invoke.html#asio.reference.asio_handler_invoke.example">Example</a>
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</h5>
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<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">my_handler</span><span class="special">;</span>
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<span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Function</span><span class="special">></span>
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<span class="keyword">void</span> <span class="identifier">asio_handler_invoke</span><span class="special">(</span><span class="identifier">Function</span> <span class="identifier">function</span><span class="special">,</span> <span class="identifier">my_handler</span><span class="special">*</span> <span class="identifier">context</span><span class="special">)</span>
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<span class="special">{</span>
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<span class="identifier">context</span><span class="special">-></span><span class="identifier">strand_</span><span class="special">.</span><span class="identifier">dispatch</span><span class="special">(</span><span class="identifier">function</span><span class="special">);</span>
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<span class="special">}</span>
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</pre>
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<h5>
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<a name="asio.reference.asio_handler_invoke.h1"></a>
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<span><a name="asio.reference.asio_handler_invoke.requirements"></a></span><a class="link" href="asio_handler_invoke.html#asio.reference.asio_handler_invoke.requirements">Requirements</a>
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</h5>
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<p>
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<span class="emphasis"><em>Header: </em></span><code class="literal">asio/handler_invoke_hook.hpp</code>
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</p>
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<p>
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<span class="emphasis"><em>Convenience header: </em></span><code class="literal">asio.hpp</code>
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</p>
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</div>
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<div class="copyright-footer">Copyright © 2003-2023 Christopher M. Kohlhoff<p>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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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>)
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</p>
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</div>
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<hr>
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<a accesskey="p" href="asio_handler_deallocate.html"><img src="../../prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../home.png" alt="Home"></a><a accesskey="n" href="asio_handler_invoke/overload1.html"><img src="../../next.png" alt="Next"></a>
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