--- /dev/null
+Boost Software License - Version 1.0 - August 17th, 2003
+
+Permission is hereby granted, free of charge, to any person or organization
+obtaining a copy of the software and accompanying documentation covered by
+this license (the "Software") to use, reproduce, display, distribute,
+execute, and transmit the Software, and to prepare derivative works of the
+Software, and to permit third-parties to whom the Software is furnished to
+do so, all subject to the following:
+
+The copyright notices in the Software and this entire statement, including
+the above license grant, this restriction and the following disclaimer,
+must be included in all copies of the Software, in whole or in part, and
+all derivative works of the Software, unless such copies or derivative
+works are solely in the form of machine-executable object code generated by
+a source language processor.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
+SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
+FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
+ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.
--- /dev/null
+//
+// coroutine.hpp
+// ~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2018 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)
+//
+
+#ifndef BOOST_ASIO_COROUTINE_HPP
+#define BOOST_ASIO_COROUTINE_HPP
+
+namespace boost {
+namespace asio {
+namespace detail {
+
+class coroutine_ref;
+
+} // namespace detail
+
+/// Provides support for implementing stackless coroutines.
+/**
+ * The @c coroutine class may be used to implement stackless coroutines. The
+ * class itself is used to store the current state of the coroutine.
+ *
+ * Coroutines are copy-constructible and assignable, and the space overhead is
+ * a single int. They can be used as a base class:
+ *
+ * @code class session : coroutine
+ * {
+ * ...
+ * }; @endcode
+ *
+ * or as a data member:
+ *
+ * @code class session
+ * {
+ * ...
+ * coroutine coro_;
+ * }; @endcode
+ *
+ * or even bound in as a function argument using lambdas or @c bind(). The
+ * important thing is that as the application maintains a copy of the object
+ * for as long as the coroutine must be kept alive.
+ *
+ * @par Pseudo-keywords
+ *
+ * A coroutine is used in conjunction with certain "pseudo-keywords", which
+ * are implemented as macros. These macros are defined by a header file:
+ *
+ * @code #include <boost/asio/yield.hpp>@endcode
+ *
+ * and may conversely be undefined as follows:
+ *
+ * @code #include <boost/asio/unyield.hpp>@endcode
+ *
+ * <b>reenter</b>
+ *
+ * The @c reenter macro is used to define the body of a coroutine. It takes a
+ * single argument: a pointer or reference to a coroutine object. For example,
+ * if the base class is a coroutine object you may write:
+ *
+ * @code reenter (this)
+ * {
+ * ... coroutine body ...
+ * } @endcode
+ *
+ * and if a data member or other variable you can write:
+ *
+ * @code reenter (coro_)
+ * {
+ * ... coroutine body ...
+ * } @endcode
+ *
+ * When @c reenter is executed at runtime, control jumps to the location of the
+ * last @c yield or @c fork.
+ *
+ * The coroutine body may also be a single statement, such as:
+ *
+ * @code reenter (this) for (;;)
+ * {
+ * ...
+ * } @endcode
+ *
+ * @b Limitation: The @c reenter macro is implemented using a switch. This
+ * means that you must take care when using local variables within the
+ * coroutine body. The local variable is not allowed in a position where
+ * reentering the coroutine could bypass the variable definition.
+ *
+ * <b>yield <em>statement</em></b>
+ *
+ * This form of the @c yield keyword is often used with asynchronous operations:
+ *
+ * @code yield socket_->async_read_some(buffer(*buffer_), *this); @endcode
+ *
+ * This divides into four logical steps:
+ *
+ * @li @c yield saves the current state of the coroutine.
+ * @li The statement initiates the asynchronous operation.
+ * @li The resume point is defined immediately following the statement.
+ * @li Control is transferred to the end of the coroutine body.
+ *
+ * When the asynchronous operation completes, the function object is invoked
+ * and @c reenter causes control to transfer to the resume point. It is
+ * important to remember to carry the coroutine state forward with the
+ * asynchronous operation. In the above snippet, the current class is a
+ * function object object with a coroutine object as base class or data member.
+ *
+ * The statement may also be a compound statement, and this permits us to
+ * define local variables with limited scope:
+ *
+ * @code yield
+ * {
+ * mutable_buffers_1 b = buffer(*buffer_);
+ * socket_->async_read_some(b, *this);
+ * } @endcode
+ *
+ * <b>yield return <em>expression</em> ;</b>
+ *
+ * This form of @c yield is often used in generators or coroutine-based parsers.
+ * For example, the function object:
+ *
+ * @code struct interleave : coroutine
+ * {
+ * istream& is1;
+ * istream& is2;
+ * char operator()(char c)
+ * {
+ * reenter (this) for (;;)
+ * {
+ * yield return is1.get();
+ * yield return is2.get();
+ * }
+ * }
+ * }; @endcode
+ *
+ * defines a trivial coroutine that interleaves the characters from two input
+ * streams.
+ *
+ * This type of @c yield divides into three logical steps:
+ *
+ * @li @c yield saves the current state of the coroutine.
+ * @li The resume point is defined immediately following the semicolon.
+ * @li The value of the expression is returned from the function.
+ *
+ * <b>yield ;</b>
+ *
+ * This form of @c yield is equivalent to the following steps:
+ *
+ * @li @c yield saves the current state of the coroutine.
+ * @li The resume point is defined immediately following the semicolon.
+ * @li Control is transferred to the end of the coroutine body.
+ *
+ * This form might be applied when coroutines are used for cooperative
+ * threading and scheduling is explicitly managed. For example:
+ *
+ * @code struct task : coroutine
+ * {
+ * ...
+ * void operator()()
+ * {
+ * reenter (this)
+ * {
+ * while (... not finished ...)
+ * {
+ * ... do something ...
+ * yield;
+ * ... do some more ...
+ * yield;
+ * }
+ * }
+ * }
+ * ...
+ * };
+ * ...
+ * task t1, t2;
+ * for (;;)
+ * {
+ * t1();
+ * t2();
+ * } @endcode
+ *
+ * <b>yield break ;</b>
+ *
+ * The final form of @c yield is used to explicitly terminate the coroutine.
+ * This form is comprised of two steps:
+ *
+ * @li @c yield sets the coroutine state to indicate termination.
+ * @li Control is transferred to the end of the coroutine body.
+ *
+ * Once terminated, calls to is_complete() return true and the coroutine cannot
+ * be reentered.
+ *
+ * Note that a coroutine may also be implicitly terminated if the coroutine
+ * body is exited without a yield, e.g. by return, throw or by running to the
+ * end of the body.
+ *
+ * <b>fork <em>statement</em></b>
+ *
+ * The @c fork pseudo-keyword is used when "forking" a coroutine, i.e. splitting
+ * it into two (or more) copies. One use of @c fork is in a server, where a new
+ * coroutine is created to handle each client connection:
+ *
+ * @code reenter (this)
+ * {
+ * do
+ * {
+ * socket_.reset(new tcp::socket(io_context_));
+ * yield acceptor->async_accept(*socket_, *this);
+ * fork server(*this)();
+ * } while (is_parent());
+ * ... client-specific handling follows ...
+ * } @endcode
+ *
+ * The logical steps involved in a @c fork are:
+ *
+ * @li @c fork saves the current state of the coroutine.
+ * @li The statement creates a copy of the coroutine and either executes it
+ * immediately or schedules it for later execution.
+ * @li The resume point is defined immediately following the semicolon.
+ * @li For the "parent", control immediately continues from the next line.
+ *
+ * The functions is_parent() and is_child() can be used to differentiate
+ * between parent and child. You would use these functions to alter subsequent
+ * control flow.
+ *
+ * Note that @c fork doesn't do the actual forking by itself. It is the
+ * application's responsibility to create a clone of the coroutine and call it.
+ * The clone can be called immediately, as above, or scheduled for delayed
+ * execution using something like io_context::post().
+ *
+ * @par Alternate macro names
+ *
+ * If preferred, an application can use macro names that follow a more typical
+ * naming convention, rather than the pseudo-keywords. These are:
+ *
+ * @li @c BOOST_ASIO_CORO_REENTER instead of @c reenter
+ * @li @c BOOST_ASIO_CORO_YIELD instead of @c yield
+ * @li @c BOOST_ASIO_CORO_FORK instead of @c fork
+ */
+class coroutine
+{
+public:
+ /// Constructs a coroutine in its initial state.
+ coroutine() : value_(0) {}
+
+ /// Returns true if the coroutine is the child of a fork.
+ bool is_child() const { return value_ < 0; }
+
+ /// Returns true if the coroutine is the parent of a fork.
+ bool is_parent() const { return !is_child(); }
+
+ /// Returns true if the coroutine has reached its terminal state.
+ bool is_complete() const { return value_ == -1; }
+
+private:
+ friend class detail::coroutine_ref;
+ int value_;
+};
+
+
+namespace detail {
+
+class coroutine_ref
+{
+public:
+ coroutine_ref(coroutine& c) : value_(c.value_), modified_(false) {}
+ coroutine_ref(coroutine* c) : value_(c->value_), modified_(false) {}
+ ~coroutine_ref() { if (!modified_) value_ = -1; }
+ operator int() const { return value_; }
+ int& operator=(int v) { modified_ = true; return value_ = v; }
+private:
+ void operator=(const coroutine_ref&);
+ int& value_;
+ bool modified_;
+};
+
+} // namespace detail
+} // namespace asio
+} // namespace boost
+
+#define BOOST_ASIO_CORO_REENTER(c) \
+ switch (::boost::asio::detail::coroutine_ref _coro_value = c) \
+ case -1: if (_coro_value) \
+ { \
+ goto terminate_coroutine; \
+ terminate_coroutine: \
+ _coro_value = -1; \
+ goto bail_out_of_coroutine; \
+ bail_out_of_coroutine: \
+ break; \
+ } \
+ else /* fall-through */ case 0:
+
+#define BOOST_ASIO_CORO_YIELD_IMPL(n) \
+ for (_coro_value = (n);;) \
+ if (_coro_value == 0) \
+ { \
+ case (n): ; \
+ break; \
+ } \
+ else \
+ switch (_coro_value ? 0 : 1) \
+ for (;;) \
+ /* fall-through */ case -1: if (_coro_value) \
+ goto terminate_coroutine; \
+ else for (;;) \
+ /* fall-through */ case 1: if (_coro_value) \
+ goto bail_out_of_coroutine; \
+ else /* fall-through */ case 0:
+
+#define BOOST_ASIO_CORO_FORK_IMPL(n) \
+ for (_coro_value = -(n);; _coro_value = (n)) \
+ if (_coro_value == (n)) \
+ { \
+ case -(n): ; \
+ break; \
+ } \
+ else
+
+#if defined(_MSC_VER)
+# define BOOST_ASIO_CORO_YIELD BOOST_ASIO_CORO_YIELD_IMPL(__COUNTER__ + 1)
+# define BOOST_ASIO_CORO_FORK BOOST_ASIO_CORO_FORK_IMPL(__COUNTER__ + 1)
+#else // defined(_MSC_VER)
+# define BOOST_ASIO_CORO_YIELD BOOST_ASIO_CORO_YIELD_IMPL(__LINE__)
+# define BOOST_ASIO_CORO_FORK BOOST_ASIO_CORO_FORK_IMPL(__LINE__)
+#endif // defined(_MSC_VER)
+
+#endif // BOOST_ASIO_COROUTINE_HPP
projects / thirdparty / kea.git / commitdiff
