Route.ih

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//
// Copyright (c) 2020 Fraunhofer Institute for Applied Information Technology (FIT)
//                    Network Research Group (NET)
//                    Schloss Birlinghoven, 53754 Sankt Augustin, GERMANY
//                    Contact: support@wiback.org
//
// This file is part of the SENF code tree.
// It is licensed under the 3-clause BSD License (aka New BSD License).
// See LICENSE.txt in the top level directory for details or visit
// https://opensource.org/licenses/BSD-3-Clause
//


/** \file
    \brief Route internal header */

#ifndef IH_SENF_PPI_Route_
#define IH_SENF_PPI_Route_ 1

// Custom includes
#include <boost/type_traits/is_convertible.hpp>
#include <boost/type_traits/is_base_of.hpp>
#include <boost/mpl/if.hpp>
#include <boost/mpl/bool.hpp>
#include <boost/static_assert.hpp>

//-/////////////////////////////////////////////////////////////////////////////////////////////////

#ifndef DOXYGEN

namespace senf {
namespace ppi {
namespace detail {

    // This is the RoutingTraits implementation for Connectors. Events are handled in the
    // specialization below
    template <class Connector, bool isEvent>
    struct RoutingTraitsImplementation
    {
        BOOST_STATIC_ASSERT((boost::is_base_of<connector::Connector, Connector>::value));

        static bool const event = false;

        static bool const notifySource = boost::is_base_of<
            connector::ActiveConnector, Connector>::value;
        static bool const notifyTarget = boost::is_base_of<
            connector::PassiveConnector, Connector>::value;

        static bool const dataSource = boost::is_base_of<
            connector::InputConnector, Connector>::value;
        static bool const dataTarget = boost::is_base_of<
            connector::OutputConnector, Connector>::value;

        typedef Connector type;
    };

    // RoutingTraits specialization for Event types. Events may be both dataSource or dataTarget but
    // cannot be notifySource.
    template <class Event>
    struct RoutingTraitsImplementation<Event,true>
    {
        static bool const event = true;

        static bool const notifySource = false;
        static bool const notifyTarget = true;

        static bool const dataSource = true;
        static bool const dataTarget = true;

        typedef EventDescriptor type;
    };

    // The RoutingTraits give routing related information about the argument type:
    //  - Whether the type is a notifySource or notifyTarget
    //  - Whether the type is dataSource or dataTarget
    //  - Provide the generalized target type
    //
    // The real implementation is in RoutingTraitsImplementation which is appropriately specialized
    // for Events
    template <class Object>
    struct RoutingTraits
        : public RoutingTraitsImplementation<Object,
                                             boost::is_convertible<Object*,
                                                                   EventDescriptor*>::value>
    {};

    // This is the generic route implementation for all routes. It just provides access to the
    // source and target.
    template <class Source, class Target, class Base>
    class BaseRouteImplementation
        : public Base
    {
    protected:
        typedef Source source_type;
        typedef Target target_type;

        Source & source() const;
        Target & target() const;

        BaseRouteImplementation(Source & source, Target & target);

    private:
        bool v_hasConnector(connector::Connector const & conn) const;
        bool v_hasEvent(EventDescriptor const & event) const;

        bool isSame(connector::Connector const & conn, connector::Connector const & other) const;
        bool isSame(connector::Connector const & conn, EventDescriptor const & other) const;
        bool isSame(EventDescriptor const & event, connector::Connector const & other) const;
        bool isSame(EventDescriptor const & event, EventDescriptor const & other) const;

        Source * source_;
        Target * target_;
    };

    // The ForwardingRouteImplementation is based on the same BaseRouteImplementation
    // as non-forwarding routes are but injects a different base-class (the third template
    // argument to BaseRouteImplementation). ForwardingRouteImplementation has two additional
    // functions:
    //  1) Register the ForwardingRoute with the notifySource
    //  2) Implement the abstract ForwardingRoute interface
    //
    // Since we don't know explicitly, which of Source or Target is the notifySource or
    // notifyTarget, the implementation calls registerRoute and notifyThrottle/notifyUnthrottle on
    // *both*, the source and target, however qualified with an additional argument of type
    // boost::mpl::bool_ which is used to select the correct overloads, of which the 'false'
    // overload always is a no-op. This way, only the correct call will generate any code, the
    // disabled call will be optimized away.
    template <class Source, class Target>
    class ForwardingRouteImplementation
        : public BaseRouteImplementation<Source, Target, ForwardingRoute>
    {
        typedef BaseRouteImplementation<Source, Target, ForwardingRoute> Base;

    protected:
        ForwardingRouteImplementation(Source & source, Target & target);
        ~ForwardingRouteImplementation();

    private:
        // send a throttle/unthrottle notification  only if the second argument is a 'true' type
        template <class T> void notifyThrottle(T & ob, boost::mpl::bool_<true> const &);
        template <class T> void notifyThrottle(T & ob, boost::mpl::bool_<false> const &);
        template <class T> void notifyUnthrottle(T & ob, boost::mpl::bool_<true> const &);
        template <class T> void notifyUnthrottle(T & ob, boost::mpl::bool_<false> const &);

        template <class T> bool throttled(T & ob, boost::mpl::bool_<true> const &) const;
        template <class T> bool throttled(T & ob, boost::mpl::bool_<false> const &) const;

        virtual void v_notifyThrottle();
        virtual void v_notifyUnthrottle();
        virtual bool v_throttled() const;
    };

    // This helper class finds the base-class suitable for a specific route. Routes are classified
    // into two groups:
    //  1) A forwarding routes is a routed which forwards notifications from a notifySource to a
    //     notifyTarget. Forwarding routes are implemented using ForwardingRouteImplementation
    //  2) Non-forwarding routes don't forward notifications. They are implemented directly
    //     using BaseRouteImplementation
    template <class Source, class Target>
    struct RouteImplementationBase
    {
        typedef RoutingTraits<Source> srcTrait;
        typedef RoutingTraits<Target> trgTrait;

        static bool const isForwarding = (srcTrait::notifySource && trgTrait::notifyTarget)
            || (srcTrait::notifyTarget && trgTrait::notifySource);

        typedef typename boost::mpl::if_c<
            isForwarding,
            ForwardingRouteImplementation<Source,Target>,
            BaseRouteImplementation<Source,Target,RouteBase> >::type base;
    };

    // RouteImplementation2 has two purposes:
    //  1) Ensure, that routing is always from a data source to a data target
    //  2) To find the correct base-class. This is delegated to RouteImplementationBase
    template <class Source, class Target>
    class RouteImplementation2
        : public RouteImplementationBase<Source,Target>::base
    {
        typedef typename RouteImplementationBase<Source,Target>::base Base;

        BOOST_STATIC_ASSERT( RoutingTraits<Source>::dataSource &&
                             RoutingTraits<Target>::dataTarget );

    protected:
        RouteImplementation2(Source & source, Target & target);
    };

    // RouteImplementation just forwards to RouteImplementation2 replacing the template arguments
    // with the appropriately generalized type: If either Source or Target is an Event type, it is
    // replaced with the general Event base-class EventDescriptor. Connector types are left as is.
    template <class Source, class Target>
    class RouteImplementation
        : public RouteImplementation2<typename RoutingTraits<Source>::type,
                                      typename RoutingTraits<Target>::type>
    {
        typedef RouteImplementation2<typename RoutingTraits<Source>::type,
                                     typename RoutingTraits<Target>::type> Base;

    protected:
        RouteImplementation(Source & source, Target & target);
    };

}}}

#endif

//-/////////////////////////////////////////////////////////////////////////////////////////////////
#endif


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