round_robin.hpp

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/*!
 * \file
 * \brief Implementation of round-robin mbox.
 */

#pragma once

#include <so_5_extra/error_ranges.hpp>

#include <so_5/impl/msg_tracing_helpers.hpp>

namespace so_5 {

namespace extra {

namespace mboxes {

namespace round_robin {

namespace errors {

/*!
 * \brief An attempt to set delivery filter to round_robin mbox.
 *
 * \since
 * v.1.0.1
 */
const int rc_delivery_filter_cannot_be_used_on_round_robin_mbox =
        so_5::extra::errors::mboxes_round_robin_errors;

} /* namespace errors */

namespace details {

//
// subscriber_info_t
//

/*!
 * \brief An information block about one subscriber.
 */
struct subscriber_info_t
{
    //! Subscriber.
    std::reference_wrapper< so_5::abstract_message_sink_t > m_sink;

    //! Constructor for the case when subscriber info is being
    //! created during event subscription.
    explicit subscriber_info_t(
        so_5::abstract_message_sink_t & sink )
        :   m_sink( sink )
    {}
};

//
// subscriber_container_t
//

/*!
 * \brief Type of container for holding subscribers for one message type.
 */
class subscriber_container_t
    {
    public :
        using storage_t = std::vector< subscriber_info_t >;

        bool
        empty() const noexcept
            {
                return m_subscribers.empty();
            }

        void
        emplace_back(
            so_5::abstract_message_sink_t & sink )
            {
                m_subscribers.emplace_back( sink );
            }

        storage_t::iterator
        end() noexcept
            {
                return m_subscribers.end();
            }

        storage_t::iterator
        find( so_5::abstract_message_sink_t & sink ) noexcept
            {
                return std::find_if( std::begin(m_subscribers), std::end(m_subscribers),
                        [&]( const auto & info ) {
                            return std::addressof( info.m_sink.get() ) ==
                                    std::addressof( sink );
                        } );
            }

        void
        erase( storage_t::iterator it ) noexcept
            {
                m_subscribers.erase(it);
                ensure_valid_current_subscriber_index();
            }

        const subscriber_info_t &
        current_subscriber() const noexcept
            {
                return m_subscribers[ m_current_subscriber ];
            }

        void
        switch_current_subscriber() noexcept
            {
                ++m_current_subscriber;
                ensure_valid_current_subscriber_index();
            }

    private :
        storage_t m_subscribers;
        storage_t::size_type m_current_subscriber{ 0 };

        void
        ensure_valid_current_subscriber_index() noexcept
            {
                if( m_current_subscriber >= m_subscribers.size() )
                    m_current_subscriber = 0;
            }
    };

//
// data_t
//

/*!
 * \brief Common part of round-robin mbox implementation.
 *
 * This part depends only on Lock type but not on tracing facilities.
 *
 * \tparam Lock type of lock object to be used.
 */
template< typename Lock >
struct data_t
    {
        //! Initializing constructor.
        data_t(
            environment_t & env,
            mbox_id_t id )
            :   m_env{ env }
            ,   m_id{ id }
            {}

        //! SObjectizer Environment to work in.
        environment_t & m_env;

        //! ID of this mbox.
        const mbox_id_t m_id;

        //! Object lock.
        Lock m_lock;

        /*!
         * \brief Map from message type to subscribers.
         */
        using messages_table_t = std::map<
                        std::type_index,
                        subscriber_container_t >;

        //! Map of subscribers to messages.
        messages_table_t m_subscribers;
    };

//
// mbox_template_t
//

//! A template with implementation of round-robin mbox.
/*!
 * \tparam Lock_Type type of lock to be used for thread safety.
 * \tparam Tracing_Base base class with implementation of message
 * delivery tracing methods. Expected to be tracing_enabled_base or
 * tracing_disabled_base from so_5::impl::msg_tracing_helpers namespace.
 */
template<
    typename Lock_Type,
    typename Tracing_Base >
class mbox_template_t
    :   public abstract_message_box_t
    ,   private data_t< Lock_Type >
    ,   private Tracing_Base
    {
        using data_type = data_t< Lock_Type >;

    public:
        //! Initializing constructor.
        template< typename... Tracing_Args >
        mbox_template_t(
            //! SObjectizer Environment to work in.
            environment_t & env,
            //! ID of this mbox.
            mbox_id_t id,
            //! Optional parameters for Tracing_Base's constructor.
            Tracing_Args &&... args )
            :   data_type{ env, id }
            ,   Tracing_Base{ std::forward< Tracing_Args >(args)... }
            {}

        mbox_id_t
        id() const override
            {
                return this->m_id;
            }

        void
        subscribe_event_handler(
            const std::type_index & msg_type,
            so_5::abstract_message_sink_t & subscriber ) override
            {
                std::lock_guard< Lock_Type > lock( this->m_lock );

                auto it = this->m_subscribers.find( msg_type );
                if( it == this->m_subscribers.end() )
                {
                    // There isn't such message type yet.
                    subscriber_container_t container;
                    container.emplace_back( subscriber );

                    this->m_subscribers.emplace( msg_type, std::move( container ) );
                }
                else
                {
                    auto & sinks = it->second;

                    auto pos = sinks.find( subscriber );
                    if( pos == sinks.end() )
                        // There is no subscriber in the container.
                        // It must be added.
                        sinks.emplace_back( subscriber );
                }
            }

        void
        unsubscribe_event_handler(
            const std::type_index & msg_type,
            so_5::abstract_message_sink_t & subscriber ) noexcept override
            {
                std::lock_guard< Lock_Type > lock( this->m_lock );

                auto it = this->m_subscribers.find( msg_type );
                if( it != this->m_subscribers.end() )
                {
                    auto & sinks = it->second;

                    auto pos = sinks.find( subscriber );
                    if( pos != sinks.end() )
                    {
                        sinks.erase( pos );
                    }

                    if( sinks.empty() )
                        this->m_subscribers.erase( it );
                }
            }

        std::string
        query_name() const override
            {
                std::ostringstream s;
                s << "<mbox:type=RRMPSC:id=" << this->m_id << ">";

                return s.str();
            }

        mbox_type_t
        type() const override
            {
                return mbox_type_t::multi_producer_single_consumer;
            }

        void
        do_deliver_message(
            so_5::message_delivery_mode_t delivery_mode,
            const std::type_index & msg_type,
            const so_5::message_ref_t & message,
            unsigned int redirection_deep ) override
            {
                typename Tracing_Base::deliver_op_tracer tracer{
                        *this, // as Tracing_Base
                        *this, // as abstract_message_box_t
                        "deliver_message",
                        delivery_mode,
                        msg_type, message, redirection_deep };

                do_deliver_message_impl(
                        tracer,
                        delivery_mode,
                        msg_type,
                        message,
                        redirection_deep );
            }

        void
        set_delivery_filter(
            const std::type_index & /*msg_type*/,
            const so_5::delivery_filter_t & /*filter*/,
            so_5::abstract_message_sink_t & /*subscriber*/ ) override
            {
                using namespace so_5::extra::mboxes::round_robin::errors;

                SO_5_THROW_EXCEPTION(
                        rc_delivery_filter_cannot_be_used_on_round_robin_mbox,
                        "set_delivery_filter is called for round_robin-mbox" );
            }

        void
        drop_delivery_filter(
            const std::type_index & /*msg_type*/,
            so_5::abstract_message_sink_t & /*subscriber*/ ) noexcept override
            {
                // Nothing to do.
            }

        so_5::environment_t &
        environment() const noexcept override
            {
                return this->m_env;
            }

    private :
        void
        do_deliver_message_impl(
            typename Tracing_Base::deliver_op_tracer const & tracer,
            so_5::message_delivery_mode_t delivery_mode,
            const std::type_index & msg_type,
            const so_5::message_ref_t & message,
            unsigned int redirection_deep )
            {
                std::lock_guard< Lock_Type > lock( this->m_lock );

                auto it = this->m_subscribers.find( msg_type );
                if( it != this->m_subscribers.end() )
                    {
                        const auto & subscriber_info = it->second.current_subscriber();
                        it->second.switch_current_subscriber();

                        do_deliver_message_to_subscriber(
                                subscriber_info,
                                tracer,
                                delivery_mode,
                                msg_type,
                                message,
                                redirection_deep );
                    }
                else
                    tracer.no_subscribers();
            }

        void
        do_deliver_message_to_subscriber(
            const subscriber_info_t & subscriber_info,
            typename Tracing_Base::deliver_op_tracer const & tracer,
            so_5::message_delivery_mode_t delivery_mode,
            const std::type_index & msg_type,
            const so_5::message_ref_t & message,
            unsigned int redirection_deep )
            {
                using namespace so_5::message_limit::impl;

                subscriber_info.m_sink.get().push_event(
                        this->m_id,
                        delivery_mode,
                        msg_type,
                        message,
                        redirection_deep,
                        tracer.overlimit_tracer() );
            }
    };

} /* namespace details */

//
// make_mbox
//
/*!
 * \brief Create an implementation of round-robin mbox.
 *
 * Usage example:
 * \code
    so_5::environment_t & env = ...;
    const so_5::mbox_t rrmbox = so_5::extra::mboxes::round_robin::make_mbox<>( env );
    ...
    so_5::send< some_message >( rrmbox, ... );
 * \endcode
 *
 * \tparam Lock_Type type of lock to be used for thread safety.
 */
template< typename Lock_Type = std::mutex >
mbox_t
make_mbox( environment_t & env )
    {
        return env.make_custom_mbox(
                []( const mbox_creation_data_t & data ) {
                    mbox_t result;

                    if( data.m_tracer.get().is_msg_tracing_enabled() )
                        {
                            using T = details::mbox_template_t<
                                    Lock_Type,
                                    ::so_5::impl::msg_tracing_helpers::tracing_enabled_base >;

                            result = mbox_t{ std::make_unique<T>(
                                    data.m_env.get(),
                                    data.m_id,
                                    data.m_tracer )
                            };
                        }
                    else
                        {
                            using T = details::mbox_template_t<
                                    Lock_Type,
                                    ::so_5::impl::msg_tracing_helpers::tracing_disabled_base >;

                            result = mbox_t{ std::make_unique<T>(
                                    data.m_env.get(),
                                    data.m_id )
                            };
                        }

                    return result;
                } );
    }

} /* namespace round_robin */

} /* namespace mboxes */

} /* namespace extra */

} /* namespace so_5 */