ceph/src/boost/libs/asio/doc/overview/coroutine.qbk

   1 [/
   2  / Copyright (c) 2003-2016 Christopher M. Kohlhoff (chris at kohlhoff dot com)
   3  /
   4  / Distributed under the Boost Software License, Version 1.0. (See accompanying
   5  / file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   6  /]
   7
   8 [section:coroutine Stackless Coroutines]
   9
  10 The [link boost_asio.reference.coroutine `coroutine`] class provides support for
  11 stackless coroutines. Stackless coroutines enable programs to implement
  12 asynchronous logic in a synchronous manner, with minimal overhead, as shown in
  13 the following example:
  14
  15   struct session : boost::asio::coroutine
  16   {
  17     boost::shared_ptr<tcp::socket> socket_;
  18     boost::shared_ptr<std::vector<char> > buffer_;
  19
  20     session(boost::shared_ptr<tcp::socket> socket)
  21       : socket_(socket),
  22         buffer_(new std::vector<char>(1024))
  23     {
  24     }
  25
  26     void operator()(boost::system::error_code ec = boost::system::error_code(), std::size_t n = 0)
  27     {
  28       if (!ec) reenter (this)
  29       {
  30         for (;;)
  31         {
  32           yield socket_->async_read_some(boost::asio::buffer(*buffer_), *this);
  33           yield boost::asio::async_write(*socket_, boost::asio::buffer(*buffer_, n), *this);
  34         }
  35       }
  36     }
  37   };
  38
  39 The `coroutine` class is used in conjunction with the pseudo-keywords
  40 `reenter`, `yield` and `fork`. These are preprocessor macros, and are
  41 implemented in terms of a `switch` statement using a technique similar to
  42 Duff's Device. The [link boost_asio.reference.coroutine `coroutine`] class's
  43 documentation provides a complete description of these pseudo-keywords.
  44
  45 [heading See Also]
  46
  47 [link boost_asio.reference.coroutine coroutine],
  48 [link boost_asio.examples.cpp03_examples.http_server_4 HTTP Server 4 example],
  49 [link boost_asio.overview.core.spawn Stackful Coroutines].
  50
  51 [endsect]