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<div class="titlepage"><div><div><h3 class="title">
<a name="asio.overview.rationale"></a><a class="link" href="rationale.html" title="Rationale">Rationale</a>
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<p>
        Most programs interact with the outside world in some way, whether it be
        via a file, a network, a serial cable, or the console. Sometimes, as is the
        case with networking, individual I/O operations can take a long time to complete.
        This poses particular challenges to application development.
      </p>
<p>
        Asio provides the tools to manage these long running operations, without
        requiring programs to use concurrency models based on threads and explicit
        locking.
      </p>
<p>
        The Asio library is intended for programmers using C++ for systems programming,
        where access to operating system functionality such as networking is often
        required. In particular, Asio addresses the following goals:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
            <span class="bold"><strong>Portability.</strong></span> The library should support
            a range of commonly used operating systems, and provide consistent behaviour
            across these operating systems.
          </li>
<li class="listitem">
            <span class="bold"><strong>Scalability.</strong></span> The library should facilitate
            the development of network applications that scale to thousands of concurrent
            connections. The library implementation for each operating system should
            use the mechanism that best enables this scalability.
          </li>
<li class="listitem">
            <span class="bold"><strong>Efficiency.</strong></span> The library should support
            techniques such as scatter-gather I/O, and allow programs to minimise
            data copying.
          </li>
<li class="listitem">
            <span class="bold"><strong>Model concepts from established APIs, such as BSD
            sockets.</strong></span> The BSD socket API is widely implemented and understood,
            and is covered in much literature. Other programming languages often
            use a similar interface for networking APIs. As far as is reasonable,
            Asio should leverage existing practice.
          </li>
<li class="listitem">
            <span class="bold"><strong>Ease of use.</strong></span> The library should provide
            a lower entry barrier for new users by taking a toolkit, rather than
            framework, approach. That is, it should try to minimise the up-front
            investment in time to just learning a few basic rules and guidelines.
            After that, a library user should only need to understand the specific
            functions that are being used.
          </li>
<li class="listitem">
            <span class="bold"><strong>Basis for further abstraction.</strong></span> The library
            should permit the development of other libraries that provide higher
            levels of abstraction. For example, implementations of commonly used
            protocols such as HTTP.
          </li>
</ul></div>
<p>
        Although Asio started life focused primarily on networking, its concepts
        of asynchronous I/O have been extended to include other operating system
        resources such as serial ports, file descriptors, and so on.
      </p>
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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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