Replace boost by the standalone asio library

1 files changed, 876 insertions, 0 deletions

diff --git a/lib/asio/io_context.hpp b/lib/asio/io_context.hpp
new file mode 100644
index 0000000..4d93be4
--- /dev/null
+++ b/lib/asio/io_context.hpp
@@ -0,0 +1,876 @@
+//
+// io_context.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 ASIO_IO_CONTEXT_HPP
+#define ASIO_IO_CONTEXT_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include <cstddef>
+#include <stdexcept>
+#include <typeinfo>
+#include "asio/async_result.hpp"
+#include "asio/detail/noncopyable.hpp"
+#include "asio/detail/wrapped_handler.hpp"
+#include "asio/error_code.hpp"
+#include "asio/execution_context.hpp"
+
+#if defined(ASIO_HAS_CHRONO)
+# include "asio/detail/chrono.hpp"
+#endif // defined(ASIO_HAS_CHRONO)
+
+#if defined(ASIO_WINDOWS) || defined(__CYGWIN__)
+# include "asio/detail/winsock_init.hpp"
+#elif defined(__sun) || defined(__QNX__) || defined(__hpux) || defined(_AIX) \
+  || defined(__osf__)
+# include "asio/detail/signal_init.hpp"
+#endif
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+namespace detail {
+#if defined(ASIO_HAS_IOCP)
+  typedef class win_iocp_io_context io_context_impl;
+  class win_iocp_overlapped_ptr;
+#else
+  typedef class scheduler io_context_impl;
+#endif
+} // namespace detail
+
+/// Provides core I/O functionality.
+/**
+ * The io_context class provides the core I/O functionality for users of the
+ * asynchronous I/O objects, including:
+ *
+ * @li asio::ip::tcp::socket
+ * @li asio::ip::tcp::acceptor
+ * @li asio::ip::udp::socket
+ * @li asio::deadline_timer.
+ *
+ * The io_context class also includes facilities intended for developers of
+ * custom asynchronous services.
+ *
+ * @par Thread Safety
+ * @e Distinct @e objects: Safe.@n
+ * @e Shared @e objects: Safe, with the specific exceptions of the restart()
+ * and notify_fork() functions. Calling restart() while there are unfinished
+ * run(), run_one(), run_for(), run_until(), poll() or poll_one() calls results
+ * in undefined behaviour. The notify_fork() function should not be called
+ * while any io_context function, or any function on an I/O object that is
+ * associated with the io_context, is being called in another thread.
+ *
+ * @par Concepts:
+ * Dispatcher.
+ *
+ * @par Synchronous and asynchronous operations
+ *
+ * Synchronous operations on I/O objects implicitly run the io_context object
+ * for an individual operation. The io_context functions run(), run_one(),
+ * run_for(), run_until(), poll() or poll_one() must be called for the
+ * io_context to perform asynchronous operations on behalf of a C++ program.
+ * Notification that an asynchronous operation has completed is delivered by
+ * invocation of the associated handler. Handlers are invoked only by a thread
+ * that is currently calling any overload of run(), run_one(), run_for(),
+ * run_until(), poll() or poll_one() for the io_context.
+ *
+ * @par Effect of exceptions thrown from handlers
+ *
+ * If an exception is thrown from a handler, the exception is allowed to
+ * propagate through the throwing thread's invocation of run(), run_one(),
+ * run_for(), run_until(), poll() or poll_one(). No other threads that are
+ * calling any of these functions are affected. It is then the responsibility
+ * of the application to catch the exception.
+ *
+ * After the exception has been caught, the run(), run_one(), run_for(),
+ * run_until(), poll() or poll_one() call may be restarted @em without the need
+ * for an intervening call to restart(). This allows the thread to rejoin the
+ * io_context object's thread pool without impacting any other threads in the
+ * pool.
+ *
+ * For example:
+ *
+ * @code
+ * asio::io_context io_context;
+ * ...
+ * for (;;)
+ * {
+ *   try
+ *   {
+ *     io_context.run();
+ *     break; // run() exited normally
+ *   }
+ *   catch (my_exception& e)
+ *   {
+ *     // Deal with exception as appropriate.
+ *   }
+ * }
+ * @endcode
+ *
+ * @par Submitting arbitrary tasks to the io_context
+ *
+ * To submit functions to the io_context, use the @ref asio::dispatch,
+ * @ref asio::post or @ref asio::defer free functions.
+ *
+ * For example:
+ *
+ * @code void my_task()
+ * {
+ *   ...
+ * }
+ *
+ * ...
+ *
+ * asio::io_context io_context;
+ *
+ * // Submit a function to the io_context.
+ * asio::post(io_context, my_task);
+ *
+ * // Submit a lambda object to the io_context.
+ * asio::post(io_context,
+ *     []()
+ *     {
+ *       ...
+ *     });
+ *
+ * // Run the io_context until it runs out of work.
+ * io_context.run(); @endcode
+ *
+ * @par Stopping the io_context from running out of work
+ *
+ * Some applications may need to prevent an io_context object's run() call from
+ * returning when there is no more work to do. For example, the io_context may
+ * be being run in a background thread that is launched prior to the
+ * application's asynchronous operations. The run() call may be kept running by
+ * creating an object of type
+ * asio::executor_work_guard<io_context::executor_type>:
+ *
+ * @code asio::io_context io_context;
+ * asio::executor_work_guard<asio::io_context::executor_type>
+ *   = asio::make_work_guard(io_context);
+ * ... @endcode
+ *
+ * To effect a shutdown, the application will then need to call the io_context
+ * object's stop() member function. This will cause the io_context run() call
+ * to return as soon as possible, abandoning unfinished operations and without
+ * permitting ready handlers to be dispatched.
+ *
+ * Alternatively, if the application requires that all operations and handlers
+ * be allowed to finish normally, the work object may be explicitly reset.
+ *
+ * @code asio::io_context io_context;
+ * asio::executor_work_guard<asio::io_context::executor_type>
+ *   = asio::make_work_guard(io_context);
+ * ...
+ * work.reset(); // Allow run() to exit. @endcode
+ */
+class io_context
+  : public execution_context
+{
+private:
+  typedef detail::io_context_impl impl_type;
+#if defined(ASIO_HAS_IOCP)
+  friend class detail::win_iocp_overlapped_ptr;
+#endif
+
+public:
+  class executor_type;
+  friend class executor_type;
+
+#if !defined(ASIO_NO_DEPRECATED)
+  class work;
+  friend class work;
+#endif // !defined(ASIO_NO_DEPRECATED)
+
+  class service;
+
+#if !defined(ASIO_NO_EXTENSIONS)
+  class strand;
+#endif // !defined(ASIO_NO_EXTENSIONS)
+
+  /// The type used to count the number of handlers executed by the context.
+  typedef std::size_t count_type;
+
+  /// Constructor.
+  ASIO_DECL io_context();
+
+  /// Constructor.
+  /**
+   * Construct with a hint about the required level of concurrency.
+   *
+   * @param concurrency_hint A suggestion to the implementation on how many
+   * threads it should allow to run simultaneously.
+   */
+  ASIO_DECL explicit io_context(int concurrency_hint);
+
+  /// Destructor.
+  /**
+   * On destruction, the io_context performs the following sequence of
+   * operations:
+   *
+   * @li For each service object @c svc in the io_context set, in reverse order
+   * of the beginning of service object lifetime, performs
+   * @c svc->shutdown().
+   *
+   * @li Uninvoked handler objects that were scheduled for deferred invocation
+   * on the io_context, or any associated strand, are destroyed.
+   *
+   * @li For each service object @c svc in the io_context set, in reverse order
+   * of the beginning of service object lifetime, performs
+   * <tt>delete static_cast<io_context::service*>(svc)</tt>.
+   *
+   * @note The destruction sequence described above permits programs to
+   * simplify their resource management by using @c shared_ptr<>. Where an
+   * object's lifetime is tied to the lifetime of a connection (or some other
+   * sequence of asynchronous operations), a @c shared_ptr to the object would
+   * be bound into the handlers for all asynchronous operations associated with
+   * it. This works as follows:
+   *
+   * @li When a single connection ends, all associated asynchronous operations
+   * complete. The corresponding handler objects are destroyed, and all
+   * @c shared_ptr references to the objects are destroyed.
+   *
+   * @li To shut down the whole program, the io_context function stop() is
+   * called to terminate any run() calls as soon as possible. The io_context
+   * destructor defined above destroys all handlers, causing all @c shared_ptr
+   * references to all connection objects to be destroyed.
+   */
+  ASIO_DECL ~io_context();
+
+  /// Obtains the executor associated with the io_context.
+  executor_type get_executor() ASIO_NOEXCEPT;
+
+  /// Run the io_context object's event processing loop.
+  /**
+   * The run() function blocks until all work has finished and there are no
+   * more handlers to be dispatched, or until the io_context has been stopped.
+   *
+   * Multiple threads may call the run() function to set up a pool of threads
+   * from which the io_context may execute handlers. All threads that are
+   * waiting in the pool are equivalent and the io_context may choose any one
+   * of them to invoke a handler.
+   *
+   * A normal exit from the run() function implies that the io_context object
+   * is stopped (the stopped() function returns @c true). Subsequent calls to
+   * run(), run_one(), poll() or poll_one() will return immediately unless there
+   * is a prior call to restart().
+   *
+   * @return The number of handlers that were executed.
+   *
+   * @note Calling the run() function from a thread that is currently calling
+   * one of run(), run_one(), run_for(), run_until(), poll() or poll_one() on
+   * the same io_context object may introduce the potential for deadlock. It is
+   * the caller's reponsibility to avoid this.
+   *
+   * The poll() function may also be used to dispatch ready handlers, but
+   * without blocking.
+   */
+  ASIO_DECL count_type run();
+
+#if !defined(ASIO_NO_DEPRECATED)
+  /// (Deprecated: Use non-error_code overload.) Run the io_context object's
+  /// event processing loop.
+  /**
+   * The run() function blocks until all work has finished and there are no
+   * more handlers to be dispatched, or until the io_context has been stopped.
+   *
+   * Multiple threads may call the run() function to set up a pool of threads
+   * from which the io_context may execute handlers. All threads that are
+   * waiting in the pool are equivalent and the io_context may choose any one
+   * of them to invoke a handler.
+   *
+   * A normal exit from the run() function implies that the io_context object
+   * is stopped (the stopped() function returns @c true). Subsequent calls to
+   * run(), run_one(), poll() or poll_one() will return immediately unless there
+   * is a prior call to restart().
+   *
+   * @param ec Set to indicate what error occurred, if any.
+   *
+   * @return The number of handlers that were executed.
+   *
+   * @note Calling the run() function from a thread that is currently calling
+   * one of run(), run_one(), run_for(), run_until(), poll() or poll_one() on
+   * the same io_context object may introduce the potential for deadlock. It is
+   * the caller's reponsibility to avoid this.
+   *
+   * The poll() function may also be used to dispatch ready handlers, but
+   * without blocking.
+   */
+  ASIO_DECL count_type run(asio::error_code& ec);
+#endif // !defined(ASIO_NO_DEPRECATED)
+
+#if defined(ASIO_HAS_CHRONO) || defined(GENERATING_DOCUMENTATION)
+  /// Run the io_context object's event processing loop for a specified
+  /// duration.
+  /**
+   * The run_for() function blocks until all work has finished and there are no
+   * more handlers to be dispatched, until the io_context has been stopped, or
+   * until the specified duration has elapsed.
+   *
+   * @param rel_time The duration for which the call may block.
+   *
+   * @return The number of handlers that were executed.
+   */
+  template <typename Rep, typename Period>
+  std::size_t run_for(const chrono::duration<Rep, Period>& rel_time);
+
+  /// Run the io_context object's event processing loop until a specified time.
+  /**
+   * The run_until() function blocks until all work has finished and there are
+   * no more handlers to be dispatched, until the io_context has been stopped,
+   * or until the specified time has been reached.
+   *
+   * @param abs_time The time point until which the call may block.
+   *
+   * @return The number of handlers that were executed.
+   */
+  template <typename Clock, typename Duration>
+  std::size_t run_until(const chrono::time_point<Clock, Duration>& abs_time);
+#endif // defined(ASIO_HAS_CHRONO) || defined(GENERATING_DOCUMENTATION)
+
+  /// Run the io_context object's event processing loop to execute at most one
+  /// handler.
+  /**
+   * The run_one() function blocks until one handler has been dispatched, or
+   * until the io_context has been stopped.
+   *
+   * @return The number of handlers that were executed. A zero return value
+   * implies that the io_context object is stopped (the stopped() function
+   * returns @c true). Subsequent calls to run(), run_one(), poll() or
+   * poll_one() will return immediately unless there is a prior call to
+   * restart().
+   *
+   * @note Calling the run_one() function from a thread that is currently
+   * calling one of run(), run_one(), run_for(), run_until(), poll() or
+   * poll_one() on the same io_context object may introduce the potential for
+   * deadlock. It is the caller's reponsibility to avoid this.
+   */
+  ASIO_DECL count_type run_one();
+
+#if !defined(ASIO_NO_DEPRECATED)
+  /// (Deprecated: Use non-error_code overlaod.) Run the io_context object's
+  /// event processing loop to execute at most one handler.
+  /**
+   * The run_one() function blocks until one handler has been dispatched, or
+   * until the io_context has been stopped.
+   *
+   * @return The number of handlers that were executed. A zero return value
+   * implies that the io_context object is stopped (the stopped() function
+   * returns @c true). Subsequent calls to run(), run_one(), poll() or
+   * poll_one() will return immediately unless there is a prior call to
+   * restart().
+   *
+   * @return The number of handlers that were executed.
+   *
+   * @note Calling the run_one() function from a thread that is currently
+   * calling one of run(), run_one(), run_for(), run_until(), poll() or
+   * poll_one() on the same io_context object may introduce the potential for
+   * deadlock. It is the caller's reponsibility to avoid this.
+   */
+  ASIO_DECL count_type run_one(asio::error_code& ec);
+#endif // !defined(ASIO_NO_DEPRECATED)
+
+#if defined(ASIO_HAS_CHRONO) || defined(GENERATING_DOCUMENTATION)
+  /// Run the io_context object's event processing loop for a specified duration
+  /// to execute at most one handler.
+  /**
+   * The run_one_for() function blocks until one handler has been dispatched,
+   * until the io_context has been stopped, or until the specified duration has
+   * elapsed.
+   *
+   * @param rel_time The duration for which the call may block.
+   *
+   * @return The number of handlers that were executed.
+   */
+  template <typename Rep, typename Period>
+  std::size_t run_one_for(const chrono::duration<Rep, Period>& rel_time);
+
+  /// Run the io_context object's event processing loop until a specified time
+  /// to execute at most one handler.
+  /**
+   * The run_one_until() function blocks until one handler has been dispatched,
+   * until the io_context has been stopped, or until the specified time has
+   * been reached.
+   *
+   * @param abs_time The time point until which the call may block.
+   *
+   * @return The number of handlers that were executed.
+   */
+  template <typename Clock, typename Duration>
+  std::size_t run_one_until(
+      const chrono::time_point<Clock, Duration>& abs_time);
+#endif // defined(ASIO_HAS_CHRONO) || defined(GENERATING_DOCUMENTATION)
+
+  /// Run the io_context object's event processing loop to execute ready
+  /// handlers.
+  /**
+   * The poll() function runs handlers that are ready to run, without blocking,
+   * until the io_context has been stopped or there are no more ready handlers.
+   *
+   * @return The number of handlers that were executed.
+   */
+  ASIO_DECL count_type poll();
+
+#if !defined(ASIO_NO_DEPRECATED)
+  /// (Deprecated: Use non-error_code overload.) Run the io_context object's
+  /// event processing loop to execute ready handlers.
+  /**
+   * The poll() function runs handlers that are ready to run, without blocking,
+   * until the io_context has been stopped or there are no more ready handlers.
+   *
+   * @param ec Set to indicate what error occurred, if any.
+   *
+   * @return The number of handlers that were executed.
+   */
+  ASIO_DECL count_type poll(asio::error_code& ec);
+#endif // !defined(ASIO_NO_DEPRECATED)
+
+  /// Run the io_context object's event processing loop to execute one ready
+  /// handler.
+  /**
+   * The poll_one() function runs at most one handler that is ready to run,
+   * without blocking.
+   *
+   * @return The number of handlers that were executed.
+   */
+  ASIO_DECL count_type poll_one();
+
+#if !defined(ASIO_NO_DEPRECATED)
+  /// (Deprecated: Use non-error_code overload.) Run the io_context object's
+  /// event processing loop to execute one ready handler.
+  /**
+   * The poll_one() function runs at most one handler that is ready to run,
+   * without blocking.
+   *
+   * @param ec Set to indicate what error occurred, if any.
+   *
+   * @return The number of handlers that were executed.
+   */
+  ASIO_DECL count_type poll_one(asio::error_code& ec);
+#endif // !defined(ASIO_NO_DEPRECATED)
+
+  /// Stop the io_context object's event processing loop.
+  /**
+   * This function does not block, but instead simply signals the io_context to
+   * stop. All invocations of its run() or run_one() member functions should
+   * return as soon as possible. Subsequent calls to run(), run_one(), poll()
+   * or poll_one() will return immediately until restart() is called.
+   */
+  ASIO_DECL void stop();
+
+  /// Determine whether the io_context object has been stopped.
+  /**
+   * This function is used to determine whether an io_context object has been
+   * stopped, either through an explicit call to stop(), or due to running out
+   * of work. When an io_context object is stopped, calls to run(), run_one(),
+   * poll() or poll_one() will return immediately without invoking any
+   * handlers.
+   *
+   * @return @c true if the io_context object is stopped, otherwise @c false.
+   */
+  ASIO_DECL bool stopped() const;
+
+  /// Restart the io_context in preparation for a subsequent run() invocation.
+  /**
+   * This function must be called prior to any second or later set of
+   * invocations of the run(), run_one(), poll() or poll_one() functions when a
+   * previous invocation of these functions returned due to the io_context
+   * being stopped or running out of work. After a call to restart(), the
+   * io_context object's stopped() function will return @c false.
+   *
+   * This function must not be called while there are any unfinished calls to
+   * the run(), run_one(), poll() or poll_one() functions.
+   */
+  ASIO_DECL void restart();
+
+#if !defined(ASIO_NO_DEPRECATED)
+  /// (Deprecated: Use restart().) Reset the io_context in preparation for a
+  /// subsequent run() invocation.
+  /**
+   * This function must be called prior to any second or later set of
+   * invocations of the run(), run_one(), poll() or poll_one() functions when a
+   * previous invocation of these functions returned due to the io_context
+   * being stopped or running out of work. After a call to restart(), the
+   * io_context object's stopped() function will return @c false.
+   *
+   * This function must not be called while there are any unfinished calls to
+   * the run(), run_one(), poll() or poll_one() functions.
+   */
+  void reset();
+
+  /// (Deprecated: Use asio::dispatch().) Request the io_context to
+  /// invoke the given handler.
+  /**
+   * This function is used to ask the io_context to execute the given handler.
+   *
+   * The io_context guarantees that the handler will only be called in a thread
+   * in which the run(), run_one(), poll() or poll_one() member functions is
+   * currently being invoked. The handler may be executed inside this function
+   * if the guarantee can be met.
+   *
+   * @param handler The handler to be called. The io_context will make
+   * a copy of the handler object as required. The function signature of the
+   * handler must be: @code void handler(); @endcode
+   *
+   * @note This function throws an exception only if:
+   *
+   * @li the handler's @c asio_handler_allocate function; or
+   *
+   * @li the handler's copy constructor
+   *
+   * throws an exception.
+   */
+  template <typename LegacyCompletionHandler>
+  ASIO_INITFN_RESULT_TYPE(LegacyCompletionHandler, void ())
+  dispatch(ASIO_MOVE_ARG(LegacyCompletionHandler) handler);
+
+  /// (Deprecated: Use asio::post().) Request the io_context to invoke
+  /// the given handler and return immediately.
+  /**
+   * This function is used to ask the io_context to execute the given handler,
+   * but without allowing the io_context to call the handler from inside this
+   * function.
+   *
+   * The io_context guarantees that the handler will only be called in a thread
+   * in which the run(), run_one(), poll() or poll_one() member functions is
+   * currently being invoked.
+   *
+   * @param handler The handler to be called. The io_context will make
+   * a copy of the handler object as required. The function signature of the
+   * handler must be: @code void handler(); @endcode
+   *
+   * @note This function throws an exception only if:
+   *
+   * @li the handler's @c asio_handler_allocate function; or
+   *
+   * @li the handler's copy constructor
+   *
+   * throws an exception.
+   */
+  template <typename LegacyCompletionHandler>
+  ASIO_INITFN_RESULT_TYPE(LegacyCompletionHandler, void ())
+  post(ASIO_MOVE_ARG(LegacyCompletionHandler) handler);
+
+  /// (Deprecated: Use asio::bind_executor().) Create a new handler that
+  /// automatically dispatches the wrapped handler on the io_context.
+  /**
+   * This function is used to create a new handler function object that, when
+   * invoked, will automatically pass the wrapped handler to the io_context
+   * object's dispatch function.
+   *
+   * @param handler The handler to be wrapped. The io_context will make a copy
+   * of the handler object as required. The function signature of the handler
+   * must be: @code void handler(A1 a1, ... An an); @endcode
+   *
+   * @return A function object that, when invoked, passes the wrapped handler to
+   * the io_context object's dispatch function. Given a function object with the
+   * signature:
+   * @code R f(A1 a1, ... An an); @endcode
+   * If this function object is passed to the wrap function like so:
+   * @code io_context.wrap(f); @endcode
+   * then the return value is a function object with the signature
+   * @code void g(A1 a1, ... An an); @endcode
+   * that, when invoked, executes code equivalent to:
+   * @code io_context.dispatch(boost::bind(f, a1, ... an)); @endcode
+   */
+  template <typename Handler>
+#if defined(GENERATING_DOCUMENTATION)
+  unspecified
+#else
+  detail::wrapped_handler<io_context&, Handler>
+#endif
+  wrap(Handler handler);
+#endif // !defined(ASIO_NO_DEPRECATED)
+
+private:
+  // Helper function to add the implementation.
+  ASIO_DECL impl_type& add_impl(impl_type* impl);
+
+  // Backwards compatible overload for use with services derived from
+  // io_context::service.
+  template <typename Service>
+  friend Service& use_service(io_context& ioc);
+
+#if defined(ASIO_WINDOWS) || defined(__CYGWIN__)
+  detail::winsock_init<> init_;
+#elif defined(__sun) || defined(__QNX__) || defined(__hpux) || defined(_AIX) \
+  || defined(__osf__)
+  detail::signal_init<> init_;
+#endif
+
+  // The implementation.
+  impl_type& impl_;
+};
+
+/// Executor used to submit functions to an io_context.
+class io_context::executor_type
+{
+public:
+  /// Obtain the underlying execution context.
+  io_context& context() const ASIO_NOEXCEPT;
+
+  /// Inform the io_context that it has some outstanding work to do.
+  /**
+   * This function is used to inform the io_context that some work has begun.
+   * This ensures that the io_context's run() and run_one() functions do not
+   * exit while the work is underway.
+   */
+  void on_work_started() const ASIO_NOEXCEPT;
+
+  /// Inform the io_context that some work is no longer outstanding.
+  /**
+   * This function is used to inform the io_context that some work has
+   * finished. Once the count of unfinished work reaches zero, the io_context
+   * is stopped and the run() and run_one() functions may exit.
+   */
+  void on_work_finished() const ASIO_NOEXCEPT;
+
+  /// Request the io_context to invoke the given function object.
+  /**
+   * This function is used to ask the io_context to execute the given function
+   * object. If the current thread is running the io_context, @c dispatch()
+   * executes the function before returning. Otherwise, the function will be
+   * scheduled to run on the io_context.
+   *
+   * @param f The function object to be called. The executor will make a copy
+   * of the handler object as required. The function signature of the function
+   * object must be: @code void function(); @endcode
+   *
+   * @param a An allocator that may be used by the executor to allocate the
+   * internal storage needed for function invocation.
+   */
+  template <typename Function, typename Allocator>
+  void dispatch(ASIO_MOVE_ARG(Function) f, const Allocator& a) const;
+
+  /// Request the io_context to invoke the given function object.
+  /**
+   * This function is used to ask the io_context to execute the given function
+   * object. The function object will never be executed inside @c post().
+   * Instead, it will be scheduled to run on the io_context.
+   *
+   * @param f The function object to be called. The executor will make a copy
+   * of the handler object as required. The function signature of the function
+   * object must be: @code void function(); @endcode
+   *
+   * @param a An allocator that may be used by the executor to allocate the
+   * internal storage needed for function invocation.
+   */
+  template <typename Function, typename Allocator>
+  void post(ASIO_MOVE_ARG(Function) f, const Allocator& a) const;
+
+  /// Request the io_context to invoke the given function object.
+  /**
+   * This function is used to ask the io_context to execute the given function
+   * object. The function object will never be executed inside @c defer().
+   * Instead, it will be scheduled to run on the io_context.
+   *
+   * If the current thread belongs to the io_context, @c defer() will delay
+   * scheduling the function object until the current thread returns control to
+   * the pool.
+   *
+   * @param f The function object to be called. The executor will make a copy
+   * of the handler object as required. The function signature of the function
+   * object must be: @code void function(); @endcode
+   *
+   * @param a An allocator that may be used by the executor to allocate the
+   * internal storage needed for function invocation.
+   */
+  template <typename Function, typename Allocator>
+  void defer(ASIO_MOVE_ARG(Function) f, const Allocator& a) const;
+
+  /// Determine whether the io_context is running in the current thread.
+  /**
+   * @return @c true if the current thread is running the io_context. Otherwise
+   * returns @c false.
+   */
+  bool running_in_this_thread() const ASIO_NOEXCEPT;
+
+  /// Compare two executors for equality.
+  /**
+   * Two executors are equal if they refer to the same underlying io_context.
+   */
+  friend bool operator==(const executor_type& a,
+      const executor_type& b) ASIO_NOEXCEPT
+  {
+    return &a.io_context_ == &b.io_context_;
+  }
+
+  /// Compare two executors for inequality.
+  /**
+   * Two executors are equal if they refer to the same underlying io_context.
+   */
+  friend bool operator!=(const executor_type& a,
+      const executor_type& b) ASIO_NOEXCEPT
+  {
+    return &a.io_context_ != &b.io_context_;
+  }
+
+private:
+  friend class io_context;
+
+  // Constructor.
+  explicit executor_type(io_context& i) : io_context_(i) {}
+
+  // The underlying io_context.
+  io_context& io_context_;
+};
+
+#if !defined(ASIO_NO_DEPRECATED)
+/// (Deprecated: Use executor_work_guard.) Class to inform the io_context when
+/// it has work to do.
+/**
+ * The work class is used to inform the io_context when work starts and
+ * finishes. This ensures that the io_context object's run() function will not
+ * exit while work is underway, and that it does exit when there is no
+ * unfinished work remaining.
+ *
+ * The work class is copy-constructible so that it may be used as a data member
+ * in a handler class. It is not assignable.
+ */
+class io_context::work
+{
+public:
+  /// Constructor notifies the io_context that work is starting.
+  /**
+   * The constructor is used to inform the io_context that some work has begun.
+   * This ensures that the io_context object's run() function will not exit
+   * while the work is underway.
+   */
+  explicit work(asio::io_context& io_context);
+
+  /// Copy constructor notifies the io_context that work is starting.
+  /**
+   * The constructor is used to inform the io_context that some work has begun.
+   * This ensures that the io_context object's run() function will not exit
+   * while the work is underway.
+   */
+  work(const work& other);
+
+  /// Destructor notifies the io_context that the work is complete.
+  /**
+   * The destructor is used to inform the io_context that some work has
+   * finished. Once the count of unfinished work reaches zero, the io_context
+   * object's run() function is permitted to exit.
+   */
+  ~work();
+
+  /// Get the io_context associated with the work.
+  asio::io_context& get_io_context();
+
+  /// (Deprecated: Use get_io_context().) Get the io_context associated with the
+  /// work.
+  asio::io_context& get_io_service();
+
+private:
+  // Prevent assignment.
+  void operator=(const work& other);
+
+  // The io_context implementation.
+  detail::io_context_impl& io_context_impl_;
+};
+#endif // !defined(ASIO_NO_DEPRECATED)
+
+/// Base class for all io_context services.
+class io_context::service
+  : public execution_context::service
+{
+public:
+  /// Get the io_context object that owns the service.
+  asio::io_context& get_io_context();
+
+#if !defined(ASIO_NO_DEPRECATED)
+  /// Get the io_context object that owns the service.
+  asio::io_context& get_io_service();
+#endif // !defined(ASIO_NO_DEPRECATED)
+
+private:
+  /// Destroy all user-defined handler objects owned by the service.
+  ASIO_DECL virtual void shutdown();
+
+#if !defined(ASIO_NO_DEPRECATED)
+  /// (Deprecated: Use shutdown().) Destroy all user-defined handler objects
+  /// owned by the service.
+  ASIO_DECL virtual void shutdown_service();
+#endif // !defined(ASIO_NO_DEPRECATED)
+
+  /// Handle notification of a fork-related event to perform any necessary
+  /// housekeeping.
+  /**
+   * This function is not a pure virtual so that services only have to
+   * implement it if necessary. The default implementation does nothing.
+   */
+  ASIO_DECL virtual void notify_fork(
+      execution_context::fork_event event);
+
+#if !defined(ASIO_NO_DEPRECATED)
+  /// (Deprecated: Use notify_fork().) Handle notification of a fork-related
+  /// event to perform any necessary housekeeping.
+  /**
+   * This function is not a pure virtual so that services only have to
+   * implement it if necessary. The default implementation does nothing.
+   */
+  ASIO_DECL virtual void fork_service(
+      execution_context::fork_event event);
+#endif // !defined(ASIO_NO_DEPRECATED)
+
+protected:
+  /// Constructor.
+  /**
+   * @param owner The io_context object that owns the service.
+   */
+  ASIO_DECL service(asio::io_context& owner);
+
+  /// Destructor.
+  ASIO_DECL virtual ~service();
+};
+
+namespace detail {
+
+// Special service base class to keep classes header-file only.
+template <typename Type>
+class service_base
+  : public asio::io_context::service
+{
+public:
+  static asio::detail::service_id<Type> id;
+
+  // Constructor.
+  service_base(asio::io_context& io_context)
+    : asio::io_context::service(io_context)
+  {
+  }
+};
+
+template <typename Type>
+asio::detail::service_id<Type> service_base<Type>::id;
+
+} // namespace detail
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#include "asio/impl/io_context.hpp"
+#if defined(ASIO_HEADER_ONLY)
+# include "asio/impl/io_context.ipp"
+#endif // defined(ASIO_HEADER_ONLY)
+
+// If both io_context.hpp and strand.hpp have been included, automatically
+// include the header file needed for the io_context::strand class.
+#if !defined(ASIO_NO_EXTENSIONS)
+# if defined(ASIO_STRAND_HPP)
+#  include "asio/io_context_strand.hpp"
+# endif // defined(ASIO_STRAND_HPP)
+#endif // !defined(ASIO_NO_EXTENSIONS)
+
+#endif // ASIO_IO_CONTEXT_HPP