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<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_asio.overview.implementation"></a><a class="link" href="implementation.html" title="Platform-Specific Implementation Notes">Platform-Specific
Implementation Notes</a>
</h3></div></div></div>
<p>
This section lists platform-specific implementation details, such as the
default demultiplexing mechanism, the number of threads created internally,
and when threads are created.
</p>
<h5>
<a name="boost_asio.overview.implementation.h0"></a>
<span class="phrase"><a name="boost_asio.overview.implementation.linux_kernel_2_4"></a></span><a class="link" href="implementation.html#boost_asio.overview.implementation.linux_kernel_2_4">Linux
Kernel 2.4</a>
</h5>
<p>
Demultiplexing mechanism:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
Uses <code class="computeroutput"><span class="identifier">select</span></code> for demultiplexing.
This means that the number of file descriptors in the process cannot
be permitted to exceed <code class="computeroutput"><span class="identifier">FD_SETSIZE</span></code>.
</li></ul></div>
<p>
Threads:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
Demultiplexing using <code class="computeroutput"><span class="identifier">select</span></code>
is performed in one of the threads that calls <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run_one</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll_one</span><span class="special">()</span></code>.
</li>
<li class="listitem">
An additional thread per <code class="computeroutput"><span class="identifier">io_service</span></code>
is used to emulate asynchronous host resolution. This thread is created
on the first call to either <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code>.
</li>
</ul></div>
<p>
Scatter-Gather:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
At most <code class="computeroutput"><span class="identifier">min</span><span class="special">(</span><span class="number">64</span><span class="special">,</span><span class="identifier">IOV_MAX</span><span class="special">)</span></code> buffers may be transferred in a single
operation.
</li></ul></div>
<h5>
<a name="boost_asio.overview.implementation.h1"></a>
<span class="phrase"><a name="boost_asio.overview.implementation.linux_kernel_2_6"></a></span><a class="link" href="implementation.html#boost_asio.overview.implementation.linux_kernel_2_6">Linux
Kernel 2.6</a>
</h5>
<p>
Demultiplexing mechanism:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
Uses <code class="computeroutput"><span class="identifier">epoll</span></code> for demultiplexing.
</li></ul></div>
<p>
Threads:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
Demultiplexing using <code class="computeroutput"><span class="identifier">epoll</span></code>
is performed in one of the threads that calls <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run_one</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll_one</span><span class="special">()</span></code>.
</li>
<li class="listitem">
An additional thread per <code class="computeroutput"><span class="identifier">io_service</span></code>
is used to emulate asynchronous host resolution. This thread is created
on the first call to either <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code>.
</li>
</ul></div>
<p>
Scatter-Gather:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
At most <code class="computeroutput"><span class="identifier">min</span><span class="special">(</span><span class="number">64</span><span class="special">,</span><span class="identifier">IOV_MAX</span><span class="special">)</span></code> buffers may be transferred in a single
operation.
</li></ul></div>
<h5>
<a name="boost_asio.overview.implementation.h2"></a>
<span class="phrase"><a name="boost_asio.overview.implementation.solaris"></a></span><a class="link" href="implementation.html#boost_asio.overview.implementation.solaris">Solaris</a>
</h5>
<p>
Demultiplexing mechanism:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
Uses <code class="literal">/dev/poll</code> for demultiplexing.
</li></ul></div>
<p>
Threads:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
Demultiplexing using <code class="literal">/dev/poll</code> is performed in one
of the threads that calls <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run_one</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll_one</span><span class="special">()</span></code>.
</li>
<li class="listitem">
An additional thread per <code class="computeroutput"><span class="identifier">io_service</span></code>
is used to emulate asynchronous host resolution. This thread is created
on the first call to either <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code>.
</li>
</ul></div>
<p>
Scatter-Gather:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
At most <code class="computeroutput"><span class="identifier">min</span><span class="special">(</span><span class="number">64</span><span class="special">,</span><span class="identifier">IOV_MAX</span><span class="special">)</span></code> buffers may be transferred in a single
operation.
</li></ul></div>
<h5>
<a name="boost_asio.overview.implementation.h3"></a>
<span class="phrase"><a name="boost_asio.overview.implementation.qnx_neutrino"></a></span><a class="link" href="implementation.html#boost_asio.overview.implementation.qnx_neutrino">QNX
Neutrino</a>
</h5>
<p>
Demultiplexing mechanism:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
Uses <code class="computeroutput"><span class="identifier">select</span></code> for demultiplexing.
This means that the number of file descriptors in the process cannot
be permitted to exceed <code class="computeroutput"><span class="identifier">FD_SETSIZE</span></code>.
</li></ul></div>
<p>
Threads:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
Demultiplexing using <code class="computeroutput"><span class="identifier">select</span></code>
is performed in one of the threads that calls <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run_one</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll_one</span><span class="special">()</span></code>.
</li>
<li class="listitem">
An additional thread per <code class="computeroutput"><span class="identifier">io_service</span></code>
is used to emulate asynchronous host resolution. This thread is created
on the first call to either <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code>.
</li>
</ul></div>
<p>
Scatter-Gather:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
At most <code class="computeroutput"><span class="identifier">min</span><span class="special">(</span><span class="number">64</span><span class="special">,</span><span class="identifier">IOV_MAX</span><span class="special">)</span></code> buffers may be transferred in a single
operation.
</li></ul></div>
<h5>
<a name="boost_asio.overview.implementation.h4"></a>
<span class="phrase"><a name="boost_asio.overview.implementation.mac_os_x"></a></span><a class="link" href="implementation.html#boost_asio.overview.implementation.mac_os_x">Mac
OS X</a>
</h5>
<p>
Demultiplexing mechanism:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
Uses <code class="computeroutput"><span class="identifier">kqueue</span></code> for demultiplexing.
</li></ul></div>
<p>
Threads:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
Demultiplexing using <code class="computeroutput"><span class="identifier">kqueue</span></code>
is performed in one of the threads that calls <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run_one</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll_one</span><span class="special">()</span></code>.
</li>
<li class="listitem">
An additional thread per <code class="computeroutput"><span class="identifier">io_service</span></code>
is used to emulate asynchronous host resolution. This thread is created
on the first call to either <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code>.
</li>
</ul></div>
<p>
Scatter-Gather:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
At most <code class="computeroutput"><span class="identifier">min</span><span class="special">(</span><span class="number">64</span><span class="special">,</span><span class="identifier">IOV_MAX</span><span class="special">)</span></code> buffers may be transferred in a single
operation.
</li></ul></div>
<h5>
<a name="boost_asio.overview.implementation.h5"></a>
<span class="phrase"><a name="boost_asio.overview.implementation.freebsd"></a></span><a class="link" href="implementation.html#boost_asio.overview.implementation.freebsd">FreeBSD</a>
</h5>
<p>
Demultiplexing mechanism:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
Uses <code class="computeroutput"><span class="identifier">kqueue</span></code> for demultiplexing.
</li></ul></div>
<p>
Threads:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
Demultiplexing using <code class="computeroutput"><span class="identifier">kqueue</span></code>
is performed in one of the threads that calls <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run_one</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll_one</span><span class="special">()</span></code>.
</li>
<li class="listitem">
An additional thread per <code class="computeroutput"><span class="identifier">io_service</span></code>
is used to emulate asynchronous host resolution. This thread is created
on the first call to either <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code>.
</li>
</ul></div>
<p>
Scatter-Gather:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
At most <code class="computeroutput"><span class="identifier">min</span><span class="special">(</span><span class="number">64</span><span class="special">,</span><span class="identifier">IOV_MAX</span><span class="special">)</span></code> buffers may be transferred in a single
operation.
</li></ul></div>
<h5>
<a name="boost_asio.overview.implementation.h6"></a>
<span class="phrase"><a name="boost_asio.overview.implementation.aix"></a></span><a class="link" href="implementation.html#boost_asio.overview.implementation.aix">AIX</a>
</h5>
<p>
Demultiplexing mechanism:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
Uses <code class="computeroutput"><span class="identifier">select</span></code> for demultiplexing.
This means that the number of file descriptors in the process cannot
be permitted to exceed <code class="computeroutput"><span class="identifier">FD_SETSIZE</span></code>.
</li></ul></div>
<p>
Threads:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
Demultiplexing using <code class="computeroutput"><span class="identifier">select</span></code>
is performed in one of the threads that calls <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run_one</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll_one</span><span class="special">()</span></code>.
</li>
<li class="listitem">
An additional thread per <code class="computeroutput"><span class="identifier">io_service</span></code>
is used to emulate asynchronous host resolution. This thread is created
on the first call to either <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code>.
</li>
</ul></div>
<p>
Scatter-Gather:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
At most <code class="computeroutput"><span class="identifier">min</span><span class="special">(</span><span class="number">64</span><span class="special">,</span><span class="identifier">IOV_MAX</span><span class="special">)</span></code> buffers may be transferred in a single
operation.
</li></ul></div>
<h5>
<a name="boost_asio.overview.implementation.h7"></a>
<span class="phrase"><a name="boost_asio.overview.implementation.hp_ux"></a></span><a class="link" href="implementation.html#boost_asio.overview.implementation.hp_ux">HP-UX</a>
</h5>
<p>
Demultiplexing mechanism:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
Uses <code class="computeroutput"><span class="identifier">select</span></code> for demultiplexing.
This means that the number of file descriptors in the process cannot
be permitted to exceed <code class="computeroutput"><span class="identifier">FD_SETSIZE</span></code>.
</li></ul></div>
<p>
Threads:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
Demultiplexing using <code class="computeroutput"><span class="identifier">select</span></code>
is performed in one of the threads that calls <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run_one</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll_one</span><span class="special">()</span></code>.
</li>
<li class="listitem">
An additional thread per <code class="computeroutput"><span class="identifier">io_service</span></code>
is used to emulate asynchronous host resolution. This thread is created
on the first call to either <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code>.
</li>
</ul></div>
<p>
Scatter-Gather:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
At most <code class="computeroutput"><span class="identifier">min</span><span class="special">(</span><span class="number">64</span><span class="special">,</span><span class="identifier">IOV_MAX</span><span class="special">)</span></code> buffers may be transferred in a single
operation.
</li></ul></div>
<h5>
<a name="boost_asio.overview.implementation.h8"></a>
<span class="phrase"><a name="boost_asio.overview.implementation.tru64"></a></span><a class="link" href="implementation.html#boost_asio.overview.implementation.tru64">Tru64</a>
</h5>
<p>
Demultiplexing mechanism:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
Uses <code class="computeroutput"><span class="identifier">select</span></code> for demultiplexing.
This means that the number of file descriptors in the process cannot
be permitted to exceed <code class="computeroutput"><span class="identifier">FD_SETSIZE</span></code>.
</li></ul></div>
<p>
Threads:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
Demultiplexing using <code class="computeroutput"><span class="identifier">select</span></code>
is performed in one of the threads that calls <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run_one</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll_one</span><span class="special">()</span></code>.
</li>
<li class="listitem">
An additional thread per <code class="computeroutput"><span class="identifier">io_service</span></code>
is used to emulate asynchronous host resolution. This thread is created
on the first call to either <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code>.
</li>
</ul></div>
<p>
Scatter-Gather:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
At most <code class="computeroutput"><span class="identifier">min</span><span class="special">(</span><span class="number">64</span><span class="special">,</span><span class="identifier">IOV_MAX</span><span class="special">)</span></code> buffers may be transferred in a single
operation.
</li></ul></div>
<h5>
<a name="boost_asio.overview.implementation.h9"></a>
<span class="phrase"><a name="boost_asio.overview.implementation.windows_95__98_and_me"></a></span><a class="link" href="implementation.html#boost_asio.overview.implementation.windows_95__98_and_me">Windows
95, 98 and Me</a>
</h5>
<p>
Demultiplexing mechanism:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
Uses <code class="computeroutput"><span class="identifier">select</span></code> for demultiplexing.
</li></ul></div>
<p>
Threads:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
Demultiplexing using <code class="computeroutput"><span class="identifier">select</span></code>
is performed in one of the threads that calls <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run_one</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll_one</span><span class="special">()</span></code>.
</li>
<li class="listitem">
An additional thread per <code class="computeroutput"><span class="identifier">io_service</span></code>
is used to emulate asynchronous host resolution. This thread is created
on the first call to either <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code>.
</li>
</ul></div>
<p>
Scatter-Gather:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
For sockets, at most 16 buffers may be transferred in a single operation.
</li></ul></div>
<h5>
<a name="boost_asio.overview.implementation.h10"></a>
<span class="phrase"><a name="boost_asio.overview.implementation.windows_nt__2000__xp__2003__vista__7_and_8"></a></span><a class="link" href="implementation.html#boost_asio.overview.implementation.windows_nt__2000__xp__2003__vista__7_and_8">Windows
NT, 2000, XP, 2003, Vista, 7 and 8</a>
</h5>
<p>
Demultiplexing mechanism:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
Uses overlapped I/O and I/O completion ports for all asynchronous socket
operations except for asynchronous connect.
</li>
<li class="listitem">
Uses <code class="computeroutput"><span class="identifier">select</span></code> for emulating
asynchronous connect.
</li>
</ul></div>
<p>
Threads:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
Demultiplexing using I/O completion ports is performed in all threads
that call <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run_one</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll_one</span><span class="special">()</span></code>.
</li>
<li class="listitem">
An additional thread per <code class="computeroutput"><span class="identifier">io_service</span></code>
is used to trigger timers. This thread is created on construction of
the first <code class="computeroutput"><span class="identifier">deadline_timer</span></code>
or <code class="computeroutput"><span class="identifier">deadline_timer_service</span></code>
objects.
</li>
<li class="listitem">
An additional thread per <code class="computeroutput"><span class="identifier">io_service</span></code>
is used for the <code class="computeroutput"><span class="identifier">select</span></code>
demultiplexing. This thread is created on the first call to <code class="computeroutput"><span class="identifier">async_connect</span><span class="special">()</span></code>.
</li>
<li class="listitem">
An additional thread per <code class="computeroutput"><span class="identifier">io_service</span></code>
is used to emulate asynchronous host resolution. This thread is created
on the first call to either <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code>.
</li>
</ul></div>
<p>
Scatter-Gather:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
For sockets, at most 64 buffers may be transferred in a single operation.
</li>
<li class="listitem">
For stream-oriented handles, only one buffer may be transferred in a
single operation.
</li>
</ul></div>
<h5>
<a name="boost_asio.overview.implementation.h11"></a>
<span class="phrase"><a name="boost_asio.overview.implementation.windows_runtime"></a></span><a class="link" href="implementation.html#boost_asio.overview.implementation.windows_runtime">Windows
Runtime</a>
</h5>
<p>
Boost.Asio provides limited support for the Windows Runtime. It requires
that the language extensions be enabled. Due to the restricted facilities
exposed by the Windows Runtime API, the support comes with the following
caveats:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
The core facilities such as the <code class="computeroutput"><span class="identifier">io_service</span></code>,
<code class="computeroutput"><span class="identifier">strand</span></code>, buffers, composed
operations, timers, etc., should all work as normal.
</li>
<li class="listitem">
For sockets, only client-side TCP is supported.
</li>
<li class="listitem">
Explicit binding of a client-side TCP socket is not supported.
</li>
<li class="listitem">
The <code class="computeroutput"><span class="identifier">cancel</span><span class="special">()</span></code>
function is not supported for sockets. Asynchronous operations may only
be cancelled by closing the socket.
</li>
<li class="listitem">
Operations that use <code class="computeroutput"><span class="identifier">null_buffers</span></code>
are not supported.
</li>
<li class="listitem">
Only <code class="computeroutput"><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">no_delay</span></code> and <code class="computeroutput"><span class="identifier">socket_base</span><span class="special">::</span><span class="identifier">keep_alive</span></code>
options are supported.
</li>
<li class="listitem">
Resolvers do not support service names, only numbers. I.e. you must use
"80" rather than "http".
</li>
<li class="listitem">
Most resolver query flags have no effect.
</li>
</ul></div>
<p>
Demultiplexing mechanism:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
Uses the <code class="computeroutput"><span class="identifier">Windows</span><span class="special">::</span><span class="identifier">Networking</span><span class="special">::</span><span class="identifier">Sockets</span><span class="special">::</span><span class="identifier">StreamSocket</span></code> class to implement asynchronous
TCP socket operations.
</li></ul></div>
<p>
Threads:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
Event completions are delivered to the Windows thread pool and posted
to the <code class="computeroutput"><span class="identifier">io_service</span></code> for
the handler to be executed.
</li>
<li class="listitem">
An additional thread per <code class="computeroutput"><span class="identifier">io_service</span></code>
is used to trigger timers. This thread is created on construction of
the first timer objects.
</li>
</ul></div>
<p>
Scatter-Gather:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
For sockets, at most one buffer may be transferred in a single operation.
</li></ul></div>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2003-2015 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>
</div></td>
</tr></table>
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