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  26 <div class="titlepage"><div><div><h4 class="title">
  27 <a name="boost_asio.reference.basic_signal_set.async_wait"></a><a class="link" href="async_wait.html" title="basic_signal_set::async_wait">basic_signal_set::async_wait</a>
  28 </h4></div></div></div>
  29 <p>
  30           <a class="indexterm" name="boost_asio.indexterm.basic_signal_set.async_wait"></a>
  31 Start
  32           an asynchronous operation to wait for a signal to be delivered.
  33         </p>
  34 <pre class="programlisting">template&lt;
  35     typename <a class="link" href="../SignalHandler.html" title="Signal handler requirements">SignalHandler</a> = <a class="link" href="../asynchronous_operations.html#boost_asio.reference.asynchronous_operations.default_completion_tokens"><span class="emphasis"><em>DEFAULT</em></span></a>&gt;
  36 <a class="link" href="../asynchronous_operations.html#boost_asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type"><span class="emphasis"><em>DEDUCED</em></span></a> async_wait(
  37     SignalHandler &amp;&amp; handler = <a class="link" href="../asynchronous_operations.html#boost_asio.reference.asynchronous_operations.default_completion_tokens"><span class="emphasis"><em>DEFAULT</em></span></a>);
  38 </pre>
  39 <p>
  40           This function may be used to initiate an asynchronous wait against the
  41           signal set. It always returns immediately.
  42         </p>
  43 <p>
  44           For each call to <code class="computeroutput">async_wait()</code>, the supplied handler will be
  45           called exactly once. The handler will be called when:
  46         </p>
  47 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
  48 <li class="listitem">
  49               One of the registered signals in the signal set occurs; or
  50             </li>
  51 <li class="listitem">
  52               The signal set was cancelled, in which case the handler is passed the
  53               error code <code class="computeroutput">boost::asio::error::operation_aborted</code>.
  54             </li>
  55 </ul></div>
  56 <h6>
  57 <a name="boost_asio.reference.basic_signal_set.async_wait.h0"></a>
  58           <span class="phrase"><a name="boost_asio.reference.basic_signal_set.async_wait.parameters"></a></span><a class="link" href="async_wait.html#boost_asio.reference.basic_signal_set.async_wait.parameters">Parameters</a>
  59         </h6>
  60 <div class="variablelist">
  61 <p class="title"><b></b></p>
  62 <dl class="variablelist">
  63 <dt><span class="term">handler</span></dt>
  64 <dd>
  65 <p>
  66                 The handler to be called when the signal occurs. Copies will be made
  67                 of the handler as required. The function signature of the handler
  68                 must be:
  69 </p>
  70 <pre class="programlisting">void handler(
  71   const boost::system::error_code&amp; error, // Result of operation.
  72   int signal_number // Indicates which signal occurred.
  73 );
  74 </pre>
  75 <p>
  76                 Regardless of whether the asynchronous operation completes immediately
  77                 or not, the handler will not be invoked from within this function.
  78                 On immediate completion, invocation of the handler will be performed
  79                 in a manner equivalent to using <a class="link" href="../post.html" title="post"><code class="computeroutput">post</code></a>.
  80               </p>
  81 </dd>
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  87 <td align="right"><div class="copyright-footer">Copyright &#169; 2003-2019 Christopher M. Kohlhoff<p>
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