text: // Copyright (C) 2006 Douglas Gregor <doug.gregor -at- gmail.com>.
  
  // Use, modification and distribution is subject to 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)
  
  /** @file request.hpp
   *
   *  This header defines the class @c request, which contains a request
   *  for non-blocking communication.
   */
  #ifndef BOOST_MPI_REQUEST_HPP
  #define BOOST_MPI_REQUEST_HPP
  
  #include <boost/mpi/config.hpp>
  #include <boost/optional.hpp>
  #include <boost/shared_ptr.hpp>
  #include <boost/mpi/packed_iarchive.hpp>
  
  namespace boost { namespace mpi {
  
  class status;
  class communicator;
  
  /**
   *  @brief A request for a non-blocking send or receive.
   *
   *  This structure contains information about a non-blocking send or
   *  receive and will be returned from @c isend or @c irecv,
   *  respectively.
   */
  class BOOST_MPI_DECL request 
  {
   public:
    /**
     *  Constructs a NULL request.
     */
    request();
  
    /**
     *  Wait until the communication associated with this request has
     *  completed, then return a @c status object describing the
     *  communication.
     */
    status wait();
  
    /**
     *  Determine whether the communication associated with this request
     *  has completed successfully. If so, returns the @c status object
     *  describing the communication. Otherwise, returns an empty @c
     *  optional<> to indicate that the communication has not completed
     *  yet. Note that once @c test() returns a @c status object, the
     *  request has completed and @c wait() should not be called.
     */
    optional<status> test();
  
    /**
     *  Cancel a pending communication, assuming it has not already been
     *  completed.
     */
    void cancel();
  
   private:
    enum request_action { ra_wait, ra_test, ra_cancel };
    typedef optional<status> (*handler_type)(request* self, 
                                             request_action action);
  
    /**
     * INTERNAL ONLY
     *
     * Handles the non-blocking receive of a serialized value.
     */
    template<typename T>
    static optional<status> 
    handle_serialized_irecv(request* self, request_action action);
  
    /**
     * INTERNAL ONLY
     *
     * Handles the non-blocking receive of an array of  serialized values.
     */
    template<typename T>
    static optional<status> 
    handle_serialized_array_irecv(request* self, request_action action);
  
   public: // template friends are not portable
  
    /// INTERNAL ONLY
    MPI_Request m_requests[2];
  
    /// INTERNAL ONLY
    handler_type m_handler;
  
    /// INTERNAL ONLY
    shared_ptr<void> m_data;
  
    friend class communicator;
  };
  
  } } // end namespace boost::mpi
  
  #endif // BOOST_MPI_REQUEST_HPP
  