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<div class="titlepage"><div><div><h3 class="title">
<a name="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>
<a name="asio.overview.implementation.linux_kernel_2_4"></a><h5>
<a name="id488134"></a>
<a class="link" href="implementation.html#asio.overview.implementation.linux_kernel_2_4">Linux Kernel
2.4</a>
</h5>
<p>
Demultiplexing mechanism:
</p>
<div class="itemizedlist"><ul type="disc"><li>
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 type="disc">
<li>
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>
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 type="disc"><li>
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>
<a name="asio.overview.implementation.linux_kernel_2_6"></a><h5>
<a name="id488445"></a>
<a class="link" href="implementation.html#asio.overview.implementation.linux_kernel_2_6">Linux Kernel
2.6</a>
</h5>
<p>
Demultiplexing mechanism:
</p>
<div class="itemizedlist"><ul type="disc"><li>
Uses <code class="computeroutput"><span class="identifier">epoll</span></code> for demultiplexing.
</li></ul></div>
<p>
Threads:
</p>
<div class="itemizedlist"><ul type="disc">
<li>
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>
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 type="disc"><li>
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>
<a name="asio.overview.implementation.solaris"></a><h5>
<a name="id488744"></a>
<a class="link" href="implementation.html#asio.overview.implementation.solaris">Solaris</a>
</h5>
<p>
Demultiplexing mechanism:
</p>
<div class="itemizedlist"><ul type="disc"><li>
Uses <code class="literal">/dev/poll</code> for demultiplexing.
</li></ul></div>
<p>
Threads:
</p>
<div class="itemizedlist"><ul type="disc">
<li>
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>
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 type="disc"><li>
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>
<a name="asio.overview.implementation.qnx_neutrino"></a><h5>
<a name="id489034"></a>
<a class="link" href="implementation.html#asio.overview.implementation.qnx_neutrino">QNX Neutrino</a>
</h5>
<p>
Demultiplexing mechanism:
</p>
<div class="itemizedlist"><ul type="disc"><li>
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 type="disc">
<li>
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>
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 type="disc"><li>
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>
<a name="asio.overview.implementation.mac_os_x"></a><h5>
<a name="id489343"></a>
<a class="link" href="implementation.html#asio.overview.implementation.mac_os_x">Mac OS X</a>
</h5>
<p>
Demultiplexing mechanism:
</p>
<div class="itemizedlist"><ul type="disc"><li>
Uses <code class="computeroutput"><span class="identifier">kqueue</span></code> for demultiplexing.
</li></ul></div>
<p>
Threads:
</p>
<div class="itemizedlist"><ul type="disc">
<li>
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>
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 type="disc"><li>
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>
<a name="asio.overview.implementation.freebsd"></a><h5>
<a name="id489642"></a>
<a class="link" href="implementation.html#asio.overview.implementation.freebsd">FreeBSD</a>
</h5>
<p>
Demultiplexing mechanism:
</p>
<div class="itemizedlist"><ul type="disc"><li>
Uses <code class="computeroutput"><span class="identifier">kqueue</span></code> for demultiplexing.
</li></ul></div>
<p>
Threads:
</p>
<div class="itemizedlist"><ul type="disc">
<li>
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>
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 type="disc"><li>
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>
<a name="asio.overview.implementation.aix"></a><h5>
<a name="id489940"></a>
<a class="link" href="implementation.html#asio.overview.implementation.aix">AIX</a>
</h5>
<p>
Demultiplexing mechanism:
</p>
<div class="itemizedlist"><ul type="disc"><li>
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 type="disc">
<li>
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>
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 type="disc"><li>
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>
<a name="asio.overview.implementation.hp_ux"></a><h5>
<a name="id490250"></a>
<a class="link" href="implementation.html#asio.overview.implementation.hp_ux">HP-UX</a>
</h5>
<p>
Demultiplexing mechanism:
</p>
<div class="itemizedlist"><ul type="disc"><li>
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 type="disc">
<li>
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>
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 type="disc"><li>
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>
<a name="asio.overview.implementation.tru64"></a><h5>
<a name="id490559"></a>
<a class="link" href="implementation.html#asio.overview.implementation.tru64">Tru64</a>
</h5>
<p>
Demultiplexing mechanism:
</p>
<div class="itemizedlist"><ul type="disc"><li>
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 type="disc">
<li>
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>
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 type="disc"><li>
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>
<a name="asio.overview.implementation.windows_95__98_and_me"></a><h5>
<a name="id490870"></a>
<a class="link" href="implementation.html#asio.overview.implementation.windows_95__98_and_me">Windows
95, 98 and Me</a>
</h5>
<p>
Demultiplexing mechanism:
</p>
<div class="itemizedlist"><ul type="disc"><li>
Uses <code class="computeroutput"><span class="identifier">select</span></code> for demultiplexing.
</li></ul></div>
<p>
Threads:
</p>
<div class="itemizedlist"><ul type="disc">
<li>
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>
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 type="disc"><li>
For sockets, at most 16 buffers may be transferred in a single operation.
</li></ul></div>
<a name="asio.overview.implementation.windows_nt__2000__xp__2003_and_vista"></a><h5>
<a name="id491137"></a>
<a class="link" href="implementation.html#asio.overview.implementation.windows_nt__2000__xp__2003_and_vista">Windows
NT, 2000, XP, 2003 and Vista</a>
</h5>
<p>
Demultiplexing mechanism:
</p>
<div class="itemizedlist"><ul type="disc">
<li>
Uses overlapped I/O and I/O completion ports for all asynchronous socket
operations except for asynchronous connect.
</li>
<li>
Uses <code class="computeroutput"><span class="identifier">select</span></code> for emulating
asynchronous connect.
</li>
</ul></div>
<p>
Threads:
</p>
<div class="itemizedlist"><ul type="disc">
<li>
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>
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>
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 type="disc">
<li>
For sockets, at most 64 buffers may be transferred in a single operation.
</li>
<li>
For stream-oriented handles, only 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 - 2010 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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