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170 lines
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<title>experimental::promise</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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<a accesskey="p" href="experimental__parallel_group/signature.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="experimental__promise/cancel.html"><img src="../../next.png" alt="Next"></a>
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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.experimental__promise"></a><a class="link" href="experimental__promise.html" title="experimental::promise">experimental::promise</a>
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</h3></div></div></div>
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<p>
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<a class="indexterm" name="asio.indexterm.experimental__promise"></a>
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</p>
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<p>
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A disposable handle for an eager operation.
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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">Signature</span> <span class="special">=</span> <span class="keyword">void</span><span class="special">(),</span>
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<span class="keyword">typename</span> <a class="link" href="Executor1.html" title="Executor requirements">Executor</a> <span class="special">=</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">any_io_executor</span><span class="special">,</span>
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<span class="keyword">typename</span> <span class="identifier">Allocator</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">allocator</span><span class="special"><</span><span class="keyword">void</span><span class="special">>></span>
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<span class="keyword">struct</span> <span class="identifier">promise</span>
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</pre>
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<h5>
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<a name="asio.reference.experimental__promise.h0"></a>
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<span><a name="asio.reference.experimental__promise.member_functions"></a></span><a class="link" href="experimental__promise.html#asio.reference.experimental__promise.member_functions">Member Functions</a>
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</h5>
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<div class="informaltable"><table class="table">
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<colgroup>
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<col>
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</colgroup>
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<thead><tr>
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<p>
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Name
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</th>
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<p>
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Description
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</tr></thead>
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<tbody>
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<tr>
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<td>
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<p>
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<a class="link" href="experimental__promise/cancel.html" title="experimental::promise::cancel"><span class="bold"><strong>cancel</strong></span></a>
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</p>
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</td>
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<td>
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<p>
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Cancel the promise. Usually done through the destructor.
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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<a class="link" href="experimental__promise/completed.html" title="experimental::promise::completed"><span class="bold"><strong>completed</strong></span></a>
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</p>
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</td>
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<td>
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<p>
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Check if the promise is completed already.
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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<a class="link" href="experimental__promise/operator_lp__rp_.html" title="experimental::promise::operator()"><span class="bold"><strong>operator()</strong></span></a>
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</p>
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</td>
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<td>
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<p>
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Wait for the promise to become ready.
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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<a class="link" href="experimental__promise/promise.html" title="experimental::promise::promise"><span class="bold"><strong>promise</strong></span></a> <span class="silver">[constructor]</span>
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</p>
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</td>
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<td>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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<a class="link" href="experimental__promise/_promise.html" title="experimental::promise::~promise"><span class="bold"><strong>~promise</strong></span></a> <span class="silver">[destructor]</span>
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</p>
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</td>
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<td>
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<p>
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Destruct the promise and cancel the operation.
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</p>
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</td>
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</tr>
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</tbody>
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</table></div>
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<p>
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Signature The signature of the operation.
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</p>
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<p>
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Executor The executor to be used by the promise (taken from the operation).
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</p>
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<p>
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Allocator The allocator used for the promise. Can be set through use_allocator.
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</p>
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<p>
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A promise can be used to initiate an asynchronous option that can be completed
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later. If the promise gets destroyed before completion, the operation gets
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a cancel signal and the result is ignored.
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</p>
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<p>
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A promise fulfills the requirements of async_operation.
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</p>
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<h5>
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<a name="asio.reference.experimental__promise.h1"></a>
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<span><a name="asio.reference.experimental__promise.examples"></a></span><a class="link" href="experimental__promise.html#asio.reference.experimental__promise.examples">Examples</a>
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</h5>
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<p>
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Reading and writing from one coroutine.
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</p>
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<pre class="programlisting"><span class="identifier">awaitable</span><span class="special"><</span><span class="keyword">void</span><span class="special">></span> <span class="identifier">read_write_some</span><span class="special">(</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span> <span class="special">&</span> <span class="identifier">sock</span><span class="special">,</span>
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<span class="identifier">asio</span><span class="special">::</span><span class="identifier">mutable_buffer</span> <span class="identifier">read_buf</span><span class="special">,</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">const_buffer</span> <span class="identifier">to_write</span><span class="special">)</span>
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<span class="special">{</span>
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<span class="keyword">auto</span> <span class="identifier">p</span> <span class="special">=</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">async_read</span><span class="special">(</span><span class="identifier">read_buf</span><span class="special">,</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">use_awaitable</span><span class="special">);</span>
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<span class="identifier">co_await</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">async_write_some</span><span class="special">(</span><span class="identifier">to_write</span><span class="special">,</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">deferred</span><span class="special">);</span>
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<span class="identifier">co_await</span> <span class="identifier">p</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.experimental__promise.h2"></a>
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<span><a name="asio.reference.experimental__promise.requirements"></a></span><a class="link" href="experimental__promise.html#asio.reference.experimental__promise.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/experimental/promise.hpp</code>
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</p>
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<p>
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<span class="emphasis"><em>Convenience header: </em></span>None
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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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<div class="spirit-nav">
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<a accesskey="p" href="experimental__parallel_group/signature.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="experimental__promise/cancel.html"><img src="../../next.png" alt="Next"></a>
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