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<title>Timer service requirements</title>
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<div class="titlepage"><div><div><h3 class="title">
<a name="asio.reference.TimerService"></a><a class="link" href="TimerService.html" title="Timer service requirements">Timer service requirements</a>
</h3></div></div></div>
<p>
        A timer service must meet the requirements for an <a class="link" href="IoObjectService.html" title="I/O object service requirements">I/O
        object service</a>, as well as the additional requirements listed below.
      </p>
<p>
        In the table below, <code class="computeroutput"><span class="identifier">X</span></code> denotes
        a timer service class for time type <code class="computeroutput"><span class="identifier">Time</span></code>
        and traits type <code class="computeroutput"><span class="identifier">TimeTraits</span></code>,
        <code class="computeroutput"><span class="identifier">a</span></code> denotes a value of type
        <code class="computeroutput"><span class="identifier">X</span></code>, <code class="computeroutput"><span class="identifier">b</span></code>
        denotes a value of type <code class="computeroutput"><span class="identifier">X</span><span class="special">::</span><span class="identifier">implementation_type</span></code>,
        <code class="computeroutput"><span class="identifier">t</span></code> denotes a value of type
        <code class="computeroutput"><span class="identifier">Time</span></code>, <code class="computeroutput"><span class="identifier">d</span></code>
        denotes a value of type <code class="computeroutput"><span class="identifier">TimeTraits</span><span class="special">::</span><span class="identifier">duration_type</span></code>,
        <code class="computeroutput"><span class="identifier">e</span></code> denotes a value of type
        <code class="computeroutput"><span class="identifier">error_code</span></code>, and <code class="computeroutput"><span class="identifier">h</span></code> denotes a value meeting <a class="link" href="WaitHandler.html" title="Wait handler requirements"><code class="computeroutput"><span class="identifier">WaitHandler</span></code></a> requirements.
      </p>
<div class="table">
<a name="asio.reference.TimerService.t0"></a><p class="title"><b>Table&#160;39.&#160;TimerService requirements</b></p>
<div class="table-contents"><table class="table" summary="TimerService requirements">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                <p>
                  expression
                </p>
              </th>
<th>
                <p>
                  return type
                </p>
              </th>
<th>
                <p>
                  assertion/note<br> pre/post-condition
                </p>
              </th>
</tr></thead>
<tbody>
<tr>
<td>
                <p>
                  <code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">destroy</span><span class="special">(</span><span class="identifier">b</span><span class="special">);</span></code>
                </p>
              </td>
<td>
              </td>
<td>
                <p>
                  From <a class="link" href="IoObjectService.html" title="I/O object service requirements">IoObjectService</a>
                  requirements. Implicitly cancels asynchronous wait operations,
                  as if by calling <code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">cancel</span><span class="special">(</span><span class="identifier">b</span><span class="special">,</span> <span class="identifier">e</span><span class="special">)</span></code>.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
</p>
<pre class="programlisting"><span class="identifier">a</span><span class="special">.</span><span class="identifier">cancel</span><span class="special">(</span><span class="identifier">b</span><span class="special">,</span> <span class="identifier">e</span><span class="special">);</span>
</pre>
<p>
                </p>
              </td>
<td>
                <p>
                  <code class="computeroutput"><span class="identifier">size_t</span></code>
                </p>
              </td>
<td>
                <p>
                  Causes any outstanding asynchronous wait operations to complete
                  as soon as possible. Handlers for cancelled operations shall be
                  passed the error code <code class="computeroutput"><span class="identifier">error</span><span class="special">::</span><span class="identifier">operation_aborted</span></code>.
                  Sets <code class="computeroutput"><span class="identifier">e</span></code> to indicate
                  success or failure. Returns the number of operations that were
                  cancelled.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">expires_at</span><span class="special">(</span><span class="identifier">b</span><span class="special">);</span></code>
                </p>
              </td>
<td>
                <p>
                  <code class="computeroutput"><span class="identifier">Time</span></code>
                </p>
              </td>
<td>
              </td>
</tr>
<tr>
<td>
                <p>
</p>
<pre class="programlisting"><span class="identifier">a</span><span class="special">.</span><span class="identifier">expires_at</span><span class="special">(</span><span class="identifier">b</span><span class="special">,</span> <span class="identifier">t</span><span class="special">,</span> <span class="identifier">e</span><span class="special">);</span>
</pre>
<p>
                </p>
              </td>
<td>
                <p>
                  <code class="computeroutput"><span class="identifier">size_t</span></code>
                </p>
              </td>
<td>
                <p>
                  Implicitly cancels asynchronous wait operations, as if by calling
                  <code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">cancel</span><span class="special">(</span><span class="identifier">b</span><span class="special">,</span>
                  <span class="identifier">e</span><span class="special">)</span></code>.
                  Returns the number of operations that were cancelled.<br> post:
                  <code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">expires_at</span><span class="special">(</span><span class="identifier">b</span><span class="special">)</span>
                  <span class="special">==</span> <span class="identifier">t</span></code>.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">expires_from_now</span><span class="special">(</span><span class="identifier">b</span><span class="special">);</span></code>
                </p>
              </td>
<td>
                <p>
                  <code class="computeroutput"><span class="identifier">TimeTraits</span><span class="special">::</span><span class="identifier">duration_type</span></code>
                </p>
              </td>
<td>
                <p>
                  Returns a value equivalent to <code class="computeroutput"><span class="identifier">TimeTraits</span><span class="special">::</span><span class="identifier">subtract</span><span class="special">(</span><span class="identifier">a</span><span class="special">.</span><span class="identifier">expires_at</span><span class="special">(</span><span class="identifier">b</span><span class="special">),</span> <span class="identifier">TimeTraits</span><span class="special">::</span><span class="identifier">now</span><span class="special">())</span></code>.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
</p>
<pre class="programlisting"><span class="identifier">a</span><span class="special">.</span><span class="identifier">expires_from_now</span><span class="special">(</span><span class="identifier">b</span><span class="special">,</span> <span class="identifier">d</span><span class="special">,</span> <span class="identifier">e</span><span class="special">);</span>
</pre>
<p>
                </p>
              </td>
<td>
                <p>
                  <code class="computeroutput"><span class="identifier">size_t</span></code>
                </p>
              </td>
<td>
                <p>
                  Equivalent to <code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">expires_at</span><span class="special">(</span><span class="identifier">b</span><span class="special">,</span> <span class="identifier">TimeTraits</span><span class="special">::</span><span class="identifier">add</span><span class="special">(</span><span class="identifier">TimeTraits</span><span class="special">::</span><span class="identifier">now</span><span class="special">(),</span> <span class="identifier">d</span><span class="special">),</span> <span class="identifier">e</span><span class="special">)</span></code>.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
</p>
<pre class="programlisting"><span class="identifier">a</span><span class="special">.</span><span class="identifier">wait</span><span class="special">(</span><span class="identifier">b</span><span class="special">,</span> <span class="identifier">e</span><span class="special">);</span>
</pre>
<p>
                </p>
              </td>
<td>
                <p>
                  <code class="computeroutput"><span class="identifier">error_code</span></code>
                </p>
              </td>
<td>
                <p>
                  Sets <code class="computeroutput"><span class="identifier">e</span></code> to indicate
                  success or failure. Returns <code class="computeroutput"><span class="identifier">e</span></code>.<br>
                  post: <code class="computeroutput"><span class="special">!!</span><span class="identifier">e</span>
                  <span class="special">||</span> <span class="special">!</span><span class="identifier">TimeTraits</span><span class="special">::</span><span class="identifier">lt</span><span class="special">(</span><span class="identifier">TimeTraits</span><span class="special">::</span><span class="identifier">now</span><span class="special">(),</span>
                  <span class="identifier">a</span><span class="special">.</span><span class="identifier">expires_at</span><span class="special">(</span><span class="identifier">b</span><span class="special">))</span></code>.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
</p>
<pre class="programlisting"><span class="identifier">a</span><span class="special">.</span><span class="identifier">async_wait</span><span class="special">(</span><span class="identifier">b</span><span class="special">,</span> <span class="identifier">h</span><span class="special">);</span>
</pre>
<p>
                </p>
              </td>
<td>
              </td>
<td>
                <p>
                  Initiates an asynchronous wait operation that is performed via
                  the <code class="computeroutput"><span class="identifier">io_service</span></code>
                  object <code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">get_io_service</span><span class="special">()</span></code>
                  and behaves according to <a class="link" href="asynchronous_operations.html" title="Requirements on asynchronous operations">asynchronous
                  operation</a> requirements.<br> <br> The handler shall be
                  posted for execution only if the condition <code class="computeroutput"><span class="special">!!</span><span class="identifier">ec</span> <span class="special">||</span>
                  <span class="special">!</span><span class="identifier">TimeTraits</span><span class="special">::</span><span class="identifier">lt</span><span class="special">(</span><span class="identifier">TimeTraits</span><span class="special">::</span><span class="identifier">now</span><span class="special">(),</span> <span class="identifier">a</span><span class="special">.</span><span class="identifier">expires_at</span><span class="special">(</span><span class="identifier">b</span><span class="special">))</span></code> holds, where <code class="computeroutput"><span class="identifier">ec</span></code>
                  is the error code to be passed to the handler.
                </p>
              </td>
</tr>
</tbody>
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<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2014 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>)
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