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<title>Random access handle service requirements</title>
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<div class="titlepage"><div><div><h3 class="title">
<a name="asio.reference.RandomAccessHandleService"></a><a class="link" href="RandomAccessHandleService.html" title="Random access handle service requirements">Random access
      handle service requirements</a>
</h3></div></div></div>
<p>
        A random access handle service must meet the requirements for a <a class="link" href="HandleService.html" title="Handle service requirements">handle
        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 random access handle service class, <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">ec</span></code>
        denotes a value of type <code class="computeroutput"><span class="identifier">error_code</span></code>,
        <code class="computeroutput"><span class="identifier">o</span></code> denotes an offset of type
        boost::uint64_t, <code class="computeroutput"><span class="identifier">mb</span></code> denotes
        a value satisfying <a class="link" href="MutableBufferSequence.html" title="Mutable buffer sequence requirements">mutable
        buffer sequence</a> requirements, <code class="computeroutput"><span class="identifier">rh</span></code>
        denotes a value meeting <a class="link" href="ReadHandler.html" title="Read handler requirements"><code class="computeroutput"><span class="identifier">ReadHandler</span></code></a> requirements, <code class="computeroutput"><span class="identifier">cb</span></code> denotes a value satisfying <a class="link" href="ConstBufferSequence.html" title="Constant buffer sequence requirements">constant
        buffer sequence</a> requirements, and <code class="computeroutput"><span class="identifier">wh</span></code>
        denotes a value meeting <a class="link" href="WriteHandler.html" title="Write handler requirements"><code class="computeroutput"><span class="identifier">WriteHandler</span></code></a> requirements.
      </p>
<div class="table">
<a name="asio.reference.RandomAccessHandleService.t0"></a><p class="title"><b>Table&#160;21.&#160;RandomAccessHandleService requirements</b></p>
<div class="table-contents"><table class="table" summary="RandomAccessHandleService 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">read_some_at</span><span class="special">(</span><span class="identifier">b</span><span class="special">,</span>
                  <span class="identifier">o</span><span class="special">,</span>
                  <span class="identifier">mb</span><span class="special">,</span>
                  <span class="identifier">ec</span><span class="special">);</span></code>
                </p>
              </td>
<td>
                <p>
                  <code class="computeroutput"><span class="identifier">size_t</span></code>
                </p>
              </td>
<td>
                <p>
                  pre: <code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">is_open</span><span class="special">(</span><span class="identifier">b</span><span class="special">)</span></code>.<br>
                  <br> Reads one or more bytes of data from a handle <code class="computeroutput"><span class="identifier">b</span></code> at offset <code class="computeroutput"><span class="identifier">o</span></code>.<br>
                  <br> The mutable buffer sequence <code class="computeroutput"><span class="identifier">mb</span></code>
                  specifies memory where the data should be placed. The operation
                  shall always fill a buffer in the sequence completely before proceeding
                  to the next.<br> <br> If successful, returns the number of
                  bytes read. Otherwise returns <code class="computeroutput"><span class="number">0</span></code>.
                  If the total size of all buffers in the sequence <code class="computeroutput"><span class="identifier">mb</span></code> is <code class="computeroutput"><span class="number">0</span></code>,
                  the function shall return <code class="computeroutput"><span class="number">0</span></code>
                  immediately.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">async_read_some_at</span><span class="special">(</span><span class="identifier">b</span><span class="special">,</span>
                  <span class="identifier">o</span><span class="special">,</span>
                  <span class="identifier">mb</span><span class="special">,</span>
                  <span class="identifier">rh</span><span class="special">);</span></code>
                </p>
              </td>
<td>
                <p>
                  <code class="computeroutput"><span class="keyword">void</span></code>
                </p>
              </td>
<td>
                <p>
                  pre: <code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">is_open</span><span class="special">(</span><span class="identifier">b</span><span class="special">)</span></code>.<br>
                  <br> Initiates an asynchronous operation to read one or more
                  bytes of data from a handle <code class="computeroutput"><span class="identifier">b</span></code>
                  at offset <code class="computeroutput"><span class="identifier">o</span></code>. The
                  operation 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 mutable buffer
                  sequence <code class="computeroutput"><span class="identifier">mb</span></code> specifies
                  memory where the data should be placed. The operation shall always
                  fill a buffer in the sequence completely before proceeding to the
                  next.<br> <br> The implementation shall maintain one or more
                  copies of <code class="computeroutput"><span class="identifier">mb</span></code> until
                  such time as the read operation no longer requires access to the
                  memory specified by the buffers in the sequence. The program must
                  ensure the memory is valid until:<br> <br> &#8212; the last copy of
                  <code class="computeroutput"><span class="identifier">mb</span></code> is destroyed,
                  or<br> <br> &#8212; the handler for the asynchronous operation is invoked,<br>
                  <br> whichever comes first. If the total size of all buffers
                  in the sequence <code class="computeroutput"><span class="identifier">mb</span></code>
                  is <code class="computeroutput"><span class="number">0</span></code>, the asynchronous
                  read operation shall complete immediately and pass <code class="computeroutput"><span class="number">0</span></code> as the argument to the handler
                  that specifies the number of bytes read.<br> <br> If the operation
                  completes successfully, the <code class="computeroutput"><span class="identifier">ReadHandler</span></code>
                  object <code class="computeroutput"><span class="identifier">rh</span></code> is invoked
                  with the number of bytes transferred. Otherwise it is invoked with
                  <code class="computeroutput"><span class="number">0</span></code>.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">write_some_at</span><span class="special">(</span><span class="identifier">b</span><span class="special">,</span>
                  <span class="identifier">o</span><span class="special">,</span>
                  <span class="identifier">cb</span><span class="special">,</span>
                  <span class="identifier">ec</span><span class="special">);</span></code>
                </p>
              </td>
<td>
                <p>
                  <code class="computeroutput"><span class="identifier">size_t</span></code>
                </p>
              </td>
<td>
                <p>
                  pre: <code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">is_open</span><span class="special">(</span><span class="identifier">b</span><span class="special">)</span></code>.<br>
                  <br> Writes one or more bytes of data to a handle <code class="computeroutput"><span class="identifier">b</span></code> at offset <code class="computeroutput"><span class="identifier">o</span></code>.<br>
                  <br> The constant buffer sequence <code class="computeroutput"><span class="identifier">cb</span></code>
                  specifies memory where the data to be written is located. The operation
                  shall always write a buffer in the sequence completely before proceeding
                  to the next.<br> <br> If successful, returns the number of
                  bytes written. Otherwise returns <code class="computeroutput"><span class="number">0</span></code>.
                  If the total size of all buffers in the sequence <code class="computeroutput"><span class="identifier">cb</span></code> is <code class="computeroutput"><span class="number">0</span></code>,
                  the function shall return <code class="computeroutput"><span class="number">0</span></code>
                  immediately.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">async_write_some_at</span><span class="special">(</span><span class="identifier">b</span><span class="special">,</span>
                  <span class="identifier">o</span><span class="special">,</span>
                  <span class="identifier">cb</span><span class="special">,</span>
                  <span class="identifier">wh</span><span class="special">);</span></code>
                </p>
              </td>
<td>
                <p>
                  <code class="computeroutput"><span class="keyword">void</span></code>
                </p>
              </td>
<td>
                <p>
                  pre: <code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">is_open</span><span class="special">(</span><span class="identifier">b</span><span class="special">)</span></code>.<br>
                  <br> Initiates an asynchronous operation to write one or more
                  bytes of data to a handle <code class="computeroutput"><span class="identifier">b</span></code>
                  at offset <code class="computeroutput"><span class="identifier">o</span></code>. The
                  operation 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 constant buffer
                  sequence <code class="computeroutput"><span class="identifier">cb</span></code> specifies
                  memory where the data to be written is located. The operation shall
                  always write a buffer in the sequence completely before proceeding
                  to the next.<br> <br> The implementation shall maintain one
                  or more copies of <code class="computeroutput"><span class="identifier">cb</span></code>
                  until such time as the write operation no longer requires access
                  to the memory specified by the buffers in the sequence. The program
                  must ensure the memory is valid until:<br> <br> &#8212; the last copy
                  of <code class="computeroutput"><span class="identifier">cb</span></code> is destroyed,
                  or<br> <br> &#8212; the handler for the asynchronous operation is invoked,<br>
                  <br> whichever comes first. If the total size of all buffers
                  in the sequence <code class="computeroutput"><span class="identifier">cb</span></code>
                  is <code class="computeroutput"><span class="number">0</span></code>, the asynchronous
                  operation shall complete immediately and pass <code class="computeroutput"><span class="number">0</span></code>
                  as the argument to the handler that specifies the number of bytes
                  read.<br> <br> If the operation completes successfully, the
                  <code class="computeroutput"><span class="identifier">WriteHandler</span></code> object
                  <code class="computeroutput"><span class="identifier">wh</span></code> is invoked with
                  the number of bytes transferred. Otherwise it is invoked with
                  <code class="computeroutput"><span class="number">0</span></code>.
                </p>
              </td>
</tr>
</tbody>
</table></div>
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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>)
      </p>
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