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//
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// strand.hpp
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// ~~~~~~~~~~
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//
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// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
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//
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// Distributed under the Boost Software License, Version 1.0. (See accompanying
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// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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//
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#ifndef BOOST_ASIO_STRAND_HPP
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#define BOOST_ASIO_STRAND_HPP
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#if defined(_MSC_VER) && (_MSC_VER >= 1200)
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# pragma once
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#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
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#include <boost/asio/detail/config.hpp>
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#include <boost/asio/async_result.hpp>
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#include <boost/asio/detail/handler_type_requirements.hpp>
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#include <boost/asio/detail/strand_service.hpp>
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#include <boost/asio/detail/wrapped_handler.hpp>
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#include <boost/asio/io_service.hpp>
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#include <boost/asio/detail/push_options.hpp>
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namespace boost {
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namespace asio {
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/// Provides serialised handler execution.
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/**
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 * The io_service::strand class provides the ability to post and dispatch
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 * handlers with the guarantee that none of those handlers will execute
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 * concurrently.
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 *
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 * @par Order of handler invocation
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 * Given:
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 *
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 * @li a strand object @c s
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 *
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 * @li an object @c a meeting completion handler requirements
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 *
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 * @li an object @c a1 which is an arbitrary copy of @c a made by the
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 * implementation
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 *
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 * @li an object @c b meeting completion handler requirements
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 *
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 * @li an object @c b1 which is an arbitrary copy of @c b made by the
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 * implementation
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 *
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 * if any of the following conditions are true:
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 *
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 * @li @c s.post(a) happens-before @c s.post(b)
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 * 
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 * @li @c s.post(a) happens-before @c s.dispatch(b), where the latter is
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 * performed outside the strand
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 * 
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 * @li @c s.dispatch(a) happens-before @c s.post(b), where the former is
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 * performed outside the strand
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 * 
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 * @li @c s.dispatch(a) happens-before @c s.dispatch(b), where both are
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 * performed outside the strand
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 *   
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 * then @c asio_handler_invoke(a1, &a1) happens-before
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 * @c asio_handler_invoke(b1, &b1).
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 * 
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 * Note that in the following case:
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 * @code async_op_1(..., s.wrap(a));
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 * async_op_2(..., s.wrap(b)); @endcode
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 * the completion of the first async operation will perform @c s.dispatch(a),
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 * and the second will perform @c s.dispatch(b), but the order in which those
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 * are performed is unspecified. That is, you cannot state whether one
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 * happens-before the other. Therefore none of the above conditions are met and
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 * no ordering guarantee is made.
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 *
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 * @note The implementation makes no guarantee that handlers posted or
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 * dispatched through different @c strand objects will be invoked concurrently.
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 *
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 * @par Thread Safety
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 * @e Distinct @e objects: Safe.@n
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 * @e Shared @e objects: Safe.
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 *
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 * @par Concepts:
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 * Dispatcher.
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 */
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class io_service::strand
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{
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public:
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  /// Constructor.
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  /**
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   * Constructs the strand.
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   *
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   * @param io_service The io_service object that the strand will use to
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   * dispatch handlers that are ready to be run.
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   */
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  explicit strand(boost::asio::io_service& io_service)
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    : service_(boost::asio::use_service<
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        boost::asio::detail::strand_service>(io_service))
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  {
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    service_.construct(impl_);
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  }
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  /// Destructor.
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  /**
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   * Destroys a strand.
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   *
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   * Handlers posted through the strand that have not yet been invoked will
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   * still be dispatched in a way that meets the guarantee of non-concurrency.
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   */
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  ~strand()
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  {
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  }
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  /// Get the io_service associated with the strand.
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  /**
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   * This function may be used to obtain the io_service object that the strand
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   * uses to dispatch handlers for asynchronous operations.
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   *
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   * @return A reference to the io_service object that the strand will use to
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   * dispatch handlers. Ownership is not transferred to the caller.
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   */
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  boost::asio::io_service& get_io_service()
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  {
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    return service_.get_io_service();
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  }
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  /// Request the strand to invoke the given handler.
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  /**
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   * This function is used to ask the strand to execute the given handler.
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   *
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   * The strand object guarantees that handlers posted or dispatched through
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   * the strand will not be executed concurrently. The handler may be executed
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   * inside this function if the guarantee can be met. If this function is
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   * called from within a handler that was posted or dispatched through the same
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   * strand, then the new handler will be executed immediately.
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   *
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   * The strand's guarantee is in addition to the guarantee provided by the
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   * underlying io_service. The io_service guarantees that the handler will only
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   * be called in a thread in which the io_service's run member function is
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   * currently being invoked.
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   *
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   * @param handler The handler to be called. The strand will make a copy of the
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   * handler object as required. The function signature of the handler must be:
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   * @code void handler(); @endcode
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   */
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  template <typename CompletionHandler>
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  BOOST_ASIO_INITFN_RESULT_TYPE(CompletionHandler, void ())
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  dispatch(BOOST_ASIO_MOVE_ARG(CompletionHandler) handler)
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  {
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    // If you get an error on the following line it means that your handler does
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    // not meet the documented type requirements for a CompletionHandler.
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    BOOST_ASIO_COMPLETION_HANDLER_CHECK(CompletionHandler, handler) type_check;
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    detail::async_result_init<
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      CompletionHandler, void ()> init(
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        BOOST_ASIO_MOVE_CAST(CompletionHandler)(handler));
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    service_.dispatch(impl_, init.handler);
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    return init.result.get();
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  }
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  /// Request the strand to invoke the given handler and return
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  /// immediately.
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  /**
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   * This function is used to ask the strand to execute the given handler, but
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   * without allowing the strand to call the handler from inside this function.
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   *
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   * The strand object guarantees that handlers posted or dispatched through
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   * the strand will not be executed concurrently. The strand's guarantee is in
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   * addition to the guarantee provided by the underlying io_service. The
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   * io_service guarantees that the handler will only be called in a thread in
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   * which the io_service's run member function is currently being invoked.
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   *
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   * @param handler The handler to be called. The strand will make a copy of the
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   * handler object as required. The function signature of the handler must be:
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   * @code void handler(); @endcode
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   */
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  template <typename CompletionHandler>
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  BOOST_ASIO_INITFN_RESULT_TYPE(CompletionHandler, void ())
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  post(BOOST_ASIO_MOVE_ARG(CompletionHandler) handler)
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  {
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    // If you get an error on the following line it means that your handler does
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    // not meet the documented type requirements for a CompletionHandler.
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    BOOST_ASIO_COMPLETION_HANDLER_CHECK(CompletionHandler, handler) type_check;
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    detail::async_result_init<
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      CompletionHandler, void ()> init(
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        BOOST_ASIO_MOVE_CAST(CompletionHandler)(handler));
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    service_.post(impl_, init.handler);
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    return init.result.get();
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  }
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  /// Create a new handler that automatically dispatches the wrapped handler
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  /// on the strand.
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  /**
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   * This function is used to create a new handler function object that, when
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   * invoked, will automatically pass the wrapped handler to the strand's
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   * dispatch function.
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   *
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   * @param handler The handler to be wrapped. The strand will make a copy of
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   * the handler object as required. The function signature of the handler must
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   * be: @code void handler(A1 a1, ... An an); @endcode
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   *
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   * @return A function object that, when invoked, passes the wrapped handler to
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   * the strand's dispatch function. Given a function object with the signature:
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   * @code R f(A1 a1, ... An an); @endcode
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   * If this function object is passed to the wrap function like so:
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   * @code strand.wrap(f); @endcode
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   * then the return value is a function object with the signature
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   * @code void g(A1 a1, ... An an); @endcode
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   * that, when invoked, executes code equivalent to:
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   * @code strand.dispatch(boost::bind(f, a1, ... an)); @endcode
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   */
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  template <typename Handler>
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#if defined(GENERATING_DOCUMENTATION)
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  unspecified
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#else
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  detail::wrapped_handler<strand, Handler, detail::is_continuation_if_running>
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#endif
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  wrap(Handler handler)
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  {
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    return detail::wrapped_handler<io_service::strand, Handler,
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        detail::is_continuation_if_running>(*this, handler);
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  }
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  /// Determine whether the strand is running in the current thread.
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  /**
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   * @return @c true if the current thread is executing a handler that was
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   * submitted to the strand using post(), dispatch() or wrap(). Otherwise
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   * returns @c false.
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   */
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  bool running_in_this_thread() const
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  {
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    return service_.running_in_this_thread(impl_);
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  }
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private:
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  boost::asio::detail::strand_service& service_;
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  boost::asio::detail::strand_service::implementation_type impl_;
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};
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/// (Deprecated: Use boost::asio::io_service::strand.) Typedef for backwards
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/// compatibility.
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typedef boost::asio::io_service::strand strand;
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} // namespace asio
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} // namespace boost
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#include <boost/asio/detail/pop_options.hpp>
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#endif // BOOST_ASIO_STRAND_HPP