text: //
  // detail/strand_service.hpp
  // ~~~~~~~~~~~~~~~~~~~~~~~~~
  //
  // Copyright (c) 2003-2016 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_DETAIL_STRAND_SERVICE_HPP
  #define BOOST_ASIO_DETAIL_STRAND_SERVICE_HPP
  
  #if defined(_MSC_VER) && (_MSC_VER >= 1200)
  # pragma once
  #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
  
  #include <boost/asio/detail/config.hpp>
  #include <boost/asio/io_service.hpp>
  #include <boost/asio/detail/mutex.hpp>
  #include <boost/asio/detail/op_queue.hpp>
  #include <boost/asio/detail/operation.hpp>
  #include <boost/asio/detail/scoped_ptr.hpp>
  
  #include <boost/asio/detail/push_options.hpp>
  
  namespace boost {
  namespace asio {
  namespace detail {
  
  // Default service implementation for a strand.
  class strand_service
    : public boost::asio::detail::service_base<strand_service>
  {
  private:
    // Helper class to re-post the strand on exit.
    struct on_do_complete_exit;
  
    // Helper class to re-post the strand on exit.
    struct on_dispatch_exit;
  
  public:
  
    // The underlying implementation of a strand.
    class strand_impl
      : public operation
    {
    public:
      strand_impl();
  
    private:
      // Only this service will have access to the internal values.
      friend class strand_service;
      friend struct on_do_complete_exit;
      friend struct on_dispatch_exit;
  
      // Mutex to protect access to internal data.
      boost::asio::detail::mutex mutex_;
  
      // Indicates whether the strand is currently "locked" by a handler. This
      // means that there is a handler upcall in progress, or that the strand
      // itself has been scheduled in order to invoke some pending handlers.
      bool locked_;
  
      // The handlers that are waiting on the strand but should not be run until
      // after the next time the strand is scheduled. This queue must only be
      // modified while the mutex is locked.
      op_queue<operation> waiting_queue_;
  
      // The handlers that are ready to be run. Logically speaking, these are the
      // handlers that hold the strand's lock. The ready queue is only modified
      // from within the strand and so may be accessed without locking the mutex.
      op_queue<operation> ready_queue_;
    };
  
    typedef strand_impl* implementation_type;
  
    // Construct a new strand service for the specified io_service.
    BOOST_ASIO_DECL explicit strand_service(boost::asio::io_service& io_service);
  
    // Destroy all user-defined handler objects owned by the service.
    BOOST_ASIO_DECL void shutdown_service();
  
    // Construct a new strand implementation.
    BOOST_ASIO_DECL void construct(implementation_type& impl);
  
    // Request the io_service to invoke the given handler.
    template <typename Handler>
    void dispatch(implementation_type& impl, Handler& handler);
  
    // Request the io_service to invoke the given handler and return immediately.
    template <typename Handler>
    void post(implementation_type& impl, Handler& handler);
  
    // Determine whether the strand is running in the current thread.
    BOOST_ASIO_DECL bool running_in_this_thread(
        const implementation_type& impl) const;
  
  private:
    // Helper function to dispatch a handler. Returns true if the handler should
    // be dispatched immediately.
    BOOST_ASIO_DECL bool do_dispatch(implementation_type& impl, operation* op);
  
    // Helper fiunction to post a handler.
    BOOST_ASIO_DECL void do_post(implementation_type& impl,
        operation* op, bool is_continuation);
  
    BOOST_ASIO_DECL static void do_complete(io_service_impl* owner,
        operation* base, const boost::system::error_code& ec,
        std::size_t bytes_transferred);
  
    // The io_service implementation used to post completions.
    io_service_impl& io_service_;
  
    // Mutex to protect access to the array of implementations.
    boost::asio::detail::mutex mutex_;
  
    // Number of implementations shared between all strand objects.
  #if defined(BOOST_ASIO_STRAND_IMPLEMENTATIONS)
    enum { num_implementations = BOOST_ASIO_STRAND_IMPLEMENTATIONS };
  #else // defined(BOOST_ASIO_STRAND_IMPLEMENTATIONS)
    enum { num_implementations = 193 };
  #endif // defined(BOOST_ASIO_STRAND_IMPLEMENTATIONS)
  
    // Pool of implementations.
    scoped_ptr<strand_impl> implementations_[num_implementations];
  
    // Extra value used when hashing to prevent recycled memory locations from
    // getting the same strand implementation.
    std::size_t salt_;
  };
  
  } // namespace detail
  } // namespace asio
  } // namespace boost
  
  #include <boost/asio/detail/pop_options.hpp>
  
  #include <boost/asio/detail/impl/strand_service.hpp>
  #if defined(BOOST_ASIO_HEADER_ONLY)
  # include <boost/asio/detail/impl/strand_service.ipp>
  #endif // defined(BOOST_ASIO_HEADER_ONLY)
  
  #endif // BOOST_ASIO_DETAIL_STRAND_SERVICE_HPP
  