| // |
| // strand.hpp |
| // ~~~~~~~~~~ |
| // |
| // Copyright (c) 2003-2014 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_STRAND_HPP |
| #define ASIO_STRAND_HPP |
| |
| #if defined(_MSC_VER) && (_MSC_VER >= 1200) |
| # pragma once |
| #endif // defined(_MSC_VER) && (_MSC_VER >= 1200) |
| |
| #include "asio/detail/config.hpp" |
| #include "asio/async_result.hpp" |
| #include "asio/detail/handler_type_requirements.hpp" |
| #include "asio/detail/strand_service.hpp" |
| #include "asio/detail/wrapped_handler.hpp" |
| #include "asio/io_service.hpp" |
| |
| #include "asio/detail/push_options.hpp" |
| |
| namespace asio { |
| |
| /// Provides serialised handler execution. |
| /** |
| * The io_service::strand class provides the ability to post and dispatch |
| * handlers with the guarantee that none of those handlers will execute |
| * concurrently. |
| * |
| * @par Order of handler invocation |
| * Given: |
| * |
| * @li a strand object @c s |
| * |
| * @li an object @c a meeting completion handler requirements |
| * |
| * @li an object @c a1 which is an arbitrary copy of @c a made by the |
| * implementation |
| * |
| * @li an object @c b meeting completion handler requirements |
| * |
| * @li an object @c b1 which is an arbitrary copy of @c b made by the |
| * implementation |
| * |
| * if any of the following conditions are true: |
| * |
| * @li @c s.post(a) happens-before @c s.post(b) |
| * |
| * @li @c s.post(a) happens-before @c s.dispatch(b), where the latter is |
| * performed outside the strand |
| * |
| * @li @c s.dispatch(a) happens-before @c s.post(b), where the former is |
| * performed outside the strand |
| * |
| * @li @c s.dispatch(a) happens-before @c s.dispatch(b), where both are |
| * performed outside the strand |
| * |
| * then @c asio_handler_invoke(a1, &a1) happens-before |
| * @c asio_handler_invoke(b1, &b1). |
| * |
| * Note that in the following case: |
| * @code async_op_1(..., s.wrap(a)); |
| * async_op_2(..., s.wrap(b)); @endcode |
| * the completion of the first async operation will perform @c s.dispatch(a), |
| * and the second will perform @c s.dispatch(b), but the order in which those |
| * are performed is unspecified. That is, you cannot state whether one |
| * happens-before the other. Therefore none of the above conditions are met and |
| * no ordering guarantee is made. |
| * |
| * @note The implementation makes no guarantee that handlers posted or |
| * dispatched through different @c strand objects will be invoked concurrently. |
| * |
| * @par Thread Safety |
| * @e Distinct @e objects: Safe.@n |
| * @e Shared @e objects: Safe. |
| * |
| * @par Concepts: |
| * Dispatcher. |
| */ |
| class io_service::strand |
| { |
| public: |
| /// Constructor. |
| /** |
| * Constructs the strand. |
| * |
| * @param io_service The io_service object that the strand will use to |
| * dispatch handlers that are ready to be run. |
| */ |
| explicit strand(asio::io_service& io_service) |
| : service_(asio::use_service< |
| asio::detail::strand_service>(io_service)) |
| { |
| service_.construct(impl_); |
| } |
| |
| /// Destructor. |
| /** |
| * Destroys a strand. |
| * |
| * Handlers posted through the strand that have not yet been invoked will |
| * still be dispatched in a way that meets the guarantee of non-concurrency. |
| */ |
| ~strand() |
| { |
| } |
| |
| /// Get the io_service associated with the strand. |
| /** |
| * This function may be used to obtain the io_service object that the strand |
| * uses to dispatch handlers for asynchronous operations. |
| * |
| * @return A reference to the io_service object that the strand will use to |
| * dispatch handlers. Ownership is not transferred to the caller. |
| */ |
| asio::io_service& get_io_service() |
| { |
| return service_.get_io_service(); |
| } |
| |
| /// Request the strand to invoke the given handler. |
| /** |
| * This function is used to ask the strand to execute the given handler. |
| * |
| * The strand object guarantees that handlers posted or dispatched through |
| * the strand will not be executed concurrently. The handler may be executed |
| * inside this function if the guarantee can be met. If this function is |
| * called from within a handler that was posted or dispatched through the same |
| * strand, then the new handler will be executed immediately. |
| * |
| * The strand's guarantee is in addition to the guarantee provided by the |
| * underlying io_service. The io_service guarantees that the handler will only |
| * be called in a thread in which the io_service's run member function is |
| * currently being invoked. |
| * |
| * @param handler The handler to be called. The strand will make a copy of the |
| * handler object as required. The function signature of the handler must be: |
| * @code void handler(); @endcode |
| */ |
| template <typename CompletionHandler> |
| ASIO_INITFN_RESULT_TYPE(CompletionHandler, void ()) |
| dispatch(ASIO_MOVE_ARG(CompletionHandler) handler) |
| { |
| // If you get an error on the following line it means that your handler does |
| // not meet the documented type requirements for a CompletionHandler. |
| ASIO_COMPLETION_HANDLER_CHECK(CompletionHandler, handler) type_check; |
| |
| detail::async_result_init< |
| CompletionHandler, void ()> init( |
| ASIO_MOVE_CAST(CompletionHandler)(handler)); |
| |
| service_.dispatch(impl_, init.handler); |
| |
| return init.result.get(); |
| } |
| |
| /// Request the strand to invoke the given handler and return |
| /// immediately. |
| /** |
| * This function is used to ask the strand to execute the given handler, but |
| * without allowing the strand to call the handler from inside this function. |
| * |
| * The strand object guarantees that handlers posted or dispatched through |
| * the strand will not be executed concurrently. The strand's guarantee is in |
| * addition to the guarantee provided by the underlying io_service. The |
| * io_service guarantees that the handler will only be called in a thread in |
| * which the io_service's run member function is currently being invoked. |
| * |
| * @param handler The handler to be called. The strand will make a copy of the |
| * handler object as required. The function signature of the handler must be: |
| * @code void handler(); @endcode |
| */ |
| template <typename CompletionHandler> |
| ASIO_INITFN_RESULT_TYPE(CompletionHandler, void ()) |
| post(ASIO_MOVE_ARG(CompletionHandler) handler) |
| { |
| // If you get an error on the following line it means that your handler does |
| // not meet the documented type requirements for a CompletionHandler. |
| ASIO_COMPLETION_HANDLER_CHECK(CompletionHandler, handler) type_check; |
| |
| detail::async_result_init< |
| CompletionHandler, void ()> init( |
| ASIO_MOVE_CAST(CompletionHandler)(handler)); |
| |
| service_.post(impl_, init.handler); |
| |
| return init.result.get(); |
| } |
| |
| /// Create a new handler that automatically dispatches the wrapped handler |
| /// on the strand. |
| /** |
| * This function is used to create a new handler function object that, when |
| * invoked, will automatically pass the wrapped handler to the strand's |
| * dispatch function. |
| * |
| * @param handler The handler to be wrapped. The strand 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 strand'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 strand.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 strand.dispatch(boost::bind(f, a1, ... an)); @endcode |
| */ |
| template <typename Handler> |
| #if defined(GENERATING_DOCUMENTATION) |
| unspecified |
| #else |
| detail::wrapped_handler<strand, Handler, detail::is_continuation_if_running> |
| #endif |
| wrap(Handler handler) |
| { |
| return detail::wrapped_handler<io_service::strand, Handler, |
| detail::is_continuation_if_running>(*this, handler); |
| } |
| |
| /// Determine whether the strand is running in the current thread. |
| /** |
| * @return @c true if the current thread is executing a handler that was |
| * submitted to the strand using post(), dispatch() or wrap(). Otherwise |
| * returns @c false. |
| */ |
| bool running_in_this_thread() const |
| { |
| return service_.running_in_this_thread(impl_); |
| } |
| |
| private: |
| asio::detail::strand_service& service_; |
| asio::detail::strand_service::implementation_type impl_; |
| }; |
| |
| /// Typedef for backwards compatibility. |
| typedef asio::io_service::strand strand; |
| |
| } // namespace asio |
| |
| #include "asio/detail/pop_options.hpp" |
| |
| #endif // ASIO_STRAND_HPP |