| [/ |
| / Copyright (c) 2003-2013 Christopher M. Kohlhoff (chris at kohlhoff dot com) |
| / |
| / Distributed under the Boost Software License, Version 1.0. (See accompanying |
| / file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) |
| /] |
| |
| [section:coroutine Stackless Coroutines] |
| |
| The [link asio.reference.coroutine `coroutine`] class provides support for |
| stackless coroutines. Stackless coroutines enable programs to implement |
| asynchronous logic in a synchronous manner, with minimal overhead, as shown in |
| the following example: |
| |
| struct session : asio::coroutine |
| { |
| boost::shared_ptr<tcp::socket> socket_; |
| boost::shared_ptr<std::vector<char> > buffer_; |
| |
| session(boost::shared_ptr<tcp::socket> socket) |
| : socket_(socket), |
| buffer_(new std::vector<char>(1024)) |
| { |
| } |
| |
| void operator()(asio::error_code ec = asio::error_code(), std::size_t n = 0) |
| { |
| if (!ec) reenter (this) |
| { |
| for (;;) |
| { |
| yield socket_->async_read_some(asio::buffer(*buffer_), *this); |
| yield asio::async_write(*socket_, asio::buffer(*buffer_, n), *this); |
| } |
| } |
| } |
| }; |
| |
| The `coroutine` class is used in conjunction with the pseudo-keywords |
| `reenter`, `yield` and `fork`. These are preprocessor macros, and are |
| implemented in terms of a `switch` statement using a technique similar to |
| Duff's Device. The [link asio.reference.coroutine `coroutine`] class's |
| documentation provides a complete description of these pseudo-keywords. |
| |
| [heading See Also] |
| |
| [link asio.reference.coroutine coroutine], |
| [link asio.examples.cpp03_examples.http_server_4 HTTP Server 4 example], |
| [link asio.overview.core.spawn Stackful Coroutines]. |
| |
| [endsect] |