dlib C++ Library - bsp.cpp

    // Copyright (C) 2012  Davis E. King (davis@dlib.net)
    // License: Boost Software License   See LICENSE.txt for the full license.
    #ifndef DLIB_BSP_CPph_
    #define DLIB_BSP_CPph_

    #include "bsp.h"
    #include <memory>
    #include <stack>

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

    namespace dlib
    {

        namespace impl1
        {

            void connect_all (
                map_id_to_con& cons,
                const std::vector<network_address>& hosts,
                unsigned long node_id
            )
            {
                cons.clear();
                for (unsigned long i = 0; i < hosts.size(); ++i)
                {
                    std::unique_ptr<bsp_con> con(new bsp_con(hosts[i]));
                    dlib::serialize(node_id, con->stream); // tell the other end our node_id
                    unsigned long id = i+1;
                    cons.add(id, con);
                }
            }

            void connect_all_hostinfo (
                map_id_to_con& cons,
                const std::vector<hostinfo>& hosts,
                unsigned long node_id,
                std::string& error_string
            )
            {
                cons.clear();
                for (unsigned long i = 0; i < hosts.size(); ++i)
                {
                    try
                    {
                        std::unique_ptr<bsp_con> con(new bsp_con(hosts[i].addr));
                        dlib::serialize(node_id, con->stream); // tell the other end our node_id
                        con->stream.flush();
                        unsigned long id = hosts[i].node_id;
                        cons.add(id, con);
                    }
                    catch (std::exception&)
                    {
                        std::ostringstream sout;
                        sout << "Could not connect to " << hosts[i].addr;
                        error_string = sout.str();
                        break;
                    }
                }
            }

            void send_out_connection_orders (
                map_id_to_con& cons,
                const std::vector<network_address>& hosts
            )
            {
                // tell everyone their node ids
                cons.reset();
                while (cons.move_next())
                {
                    dlib::serialize(cons.element().key(), cons.element().value()->stream);
                }

                // now tell them who to connect to
                std::vector<hostinfo> targets;
                for (unsigned long i = 0; i < hosts.size(); ++i)
                {
                    hostinfo info(hosts[i], i+1);

                    dlib::serialize(targets, cons[info.node_id]->stream);
                    targets.push_back(info);

                    // let the other host know how many incoming connections to expect
                    const unsigned long num = hosts.size()-targets.size();
                    dlib::serialize(num, cons[info.node_id]->stream);
                    cons[info.node_id]->stream.flush();
                }
            }

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

        }

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

        namespace impl2
        {
            // These control bytes are sent before each message between nodes.  Note that many
            // of these are only sent between the control node (node 0) and the other nodes.
            // This is because the controller node is responsible for handling the
            // synchronization that needs to happen when all nodes block on calls to
            // receive_data()
            // at the same time.

            // denotes a normal content message.
            const static char MESSAGE_HEADER            = 0;

            // sent to the controller node when someone receives a message via receive_data().
            const static char GOT_MESSAGE               = 1;

            // sent to the controller node when someone sends a message via send().
            const static char SENT_MESSAGE              = 2;

            // sent to the controller node when someone enters a call to receive_data()
            const static char IN_WAITING_STATE          = 3;

            // broadcast when a node terminates itself.
            const static char NODE_TERMINATE            = 5;

            // broadcast by the controller node when it determines that all nodes are blocked
            // on calls to receive_data() and there aren't any messages in flight.  This is also
            // what makes us go to the next epoch.
            const static char SEE_ALL_IN_WAITING_STATE  = 6;

            // This isn't ever transmitted between nodes.  It is used internally to indicate
            // that an error occurred.
            const static char READ_ERROR                = 7;

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

            void read_thread (
                impl1::bsp_con* con,
                unsigned long node_id,
                unsigned long sender_id,
                impl1::thread_safe_message_queue& msg_buffer
            )
            {
                try
                {
                    while(true)
                    {
                        impl1::msg_data msg;
                        deserialize(msg.msg_type, con->stream);
                        msg.sender_id = sender_id;

                        if (msg.msg_type == MESSAGE_HEADER)
                        {
                            msg.data.reset(new std::vector<char>);
                            deserialize(msg.epoch, con->stream);
                            deserialize(*msg.data, con->stream);
                        }

                        msg_buffer.push_and_consume(msg);

                        if (msg.msg_type == NODE_TERMINATE)
                            break;
                    }
                }
                catch (std::exception& e)
                {
                    impl1::msg_data msg;
                    msg.data.reset(new std::vector<char>);
                    vectorstream sout(*msg.data);
                    sout << "An exception was thrown while attempting to receive a message from processing node " << sender_id << ".\n";
                    sout << "  Sending processing node address:   " << con->con->get_foreign_ip() << ":" << con->con->get_foreign_port() << std::endl;
                    sout << "  Receiving processing node address: " << con->con->get_local_ip() << ":" << con->con->get_local_port() << std::endl;
                    sout << "  Receiving processing node id:      " << node_id << std::endl;
                    sout << "  Error message in the exception:    " << e.what() << std::endl;

                    msg.sender_id = sender_id;
                    msg.msg_type = READ_ERROR;

                    msg_buffer.push_and_consume(msg);
                }
                catch (...)
                {
                    impl1::msg_data msg;
                    msg.data.reset(new std::vector<char>);
                    vectorstream sout(*msg.data);
                    sout << "An exception was thrown while attempting to receive a message from processing node " << sender_id << ".\n";
                    sout << "  Sending processing node address:   " << con->con->get_foreign_ip() << ":" << con->con->get_foreign_port() << std::endl;
                    sout << "  Receiving processing node address: " << con->con->get_local_ip() << ":" << con->con->get_local_port() << std::endl;
                    sout << "  Receiving processing node id:      " << node_id << std::endl;

                    msg.sender_id = sender_id;
                    msg.msg_type = READ_ERROR;

                    msg_buffer.push_and_consume(msg);
                }
            }

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

        }

    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------
    //                          IMPLEMENTATION OF bsp_context OBJECT MEMBERS
    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------

        void bsp_context::
        close_all_connections_gracefully(
        )
        {
            if (node_id() != 0)
            {
                _cons.reset();
                while (_cons.move_next())
                {
                    // tell the other end that we are intentionally dropping the connection
                    serialize(impl2::NODE_TERMINATE,_cons.element().value()->stream);
                    _cons.element().value()->stream.flush();
                }
            }

            impl1::msg_data msg;
            // now wait for all the other nodes to terminate
            while (num_terminated_nodes < _cons.size() )
            {
                if (node_id() == 0 && num_waiting_nodes + num_terminated_nodes == _cons.size() && outstanding_messages == 0)
                {
                    num_waiting_nodes = 0;
                    broadcast_byte(impl2::SEE_ALL_IN_WAITING_STATE);
                    ++current_epoch;
                }

                if (!msg_buffer.pop(msg))
                    throw dlib::socket_error("Error reading from msg_buffer in dlib::bsp_context.");

                if (msg.msg_type == impl2::NODE_TERMINATE)
                {
                    ++num_terminated_nodes;
                    _cons[msg.sender_id]->terminated = true;
                }
                else if (msg.msg_type == impl2::READ_ERROR)
                {
                    throw dlib::socket_error(msg.data_to_string());
                }
                else if (msg.msg_type == impl2::MESSAGE_HEADER)
                {
                    throw dlib::socket_error("A BSP node received a message after it has terminated.");
                }
                else if (msg.msg_type == impl2::GOT_MESSAGE)
                {
                    --num_waiting_nodes;
                    --outstanding_messages;
                }
                else if (msg.msg_type == impl2::SENT_MESSAGE)
                {
                    ++outstanding_messages;
                }
                else if (msg.msg_type == impl2::IN_WAITING_STATE)
                {
                    ++num_waiting_nodes;
                }
            }

            if (node_id() == 0)
            {
                _cons.reset();
                while (_cons.move_next())
                {
                    // tell the other end that we are intentionally dropping the connection
                    serialize(impl2::NODE_TERMINATE,_cons.element().value()->stream);
                    _cons.element().value()->stream.flush();
                }

                if (outstanding_messages != 0)
                {
                    std::ostringstream sout;
                    sout << "A BSP job was allowed to terminate before all sent messages have been received.\n";
                    sout << "There are at least " << outstanding_messages << " messages still in flight.   Make sure all sent messages\n";
                    sout << "have a corresponding call to receive().";
                    throw dlib::socket_error(sout.str());
                }
            }
        }

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

        bsp_context::
        ~bsp_context()
        {
            _cons.reset();
            while (_cons.move_next())
            {
                _cons.element().value()->con->shutdown();
            }

            msg_buffer.disable();

            // this will wait for all the threads to terminate
            threads.clear();
        }

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

        bsp_context::
        bsp_context(
            unsigned long node_id_,
            impl1::map_id_to_con& cons_
        ) :
            outstanding_messages(0),
            num_waiting_nodes(0),
            num_terminated_nodes(0),
            current_epoch(1),
            _cons(cons_),
            _node_id(node_id_)
        {
            // spawn a bunch of read threads, one for each connection
            _cons.reset();
            while (_cons.move_next())
            {
                std::unique_ptr<thread_function> ptr(new thread_function(&impl2::read_thread,
                                                                    _cons.element().value().get(),
                                                                    _node_id,
                                                                    _cons.element().key(),
                                                                    ref(msg_buffer)));
                threads.push_back(ptr);
            }

        }

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

        bool bsp_context::
        receive_data (
            std::shared_ptr<std::vector<char> >& item,
            unsigned long& sending_node_id
        )
        {
            notify_control_node(impl2::IN_WAITING_STATE);

            while (true)
            {
                // If there aren't any nodes left to give us messages then return right now.
                // We need to check the msg_buffer size to make sure there aren't any
                // unprocessed message there.  Recall that this can happen because status
                // messages always jump to the front of the message buffer.  So we might have
                // learned about the node terminations before processing their messages for us.
                if (num_terminated_nodes == _cons.size() && msg_buffer.size() == 0)
                {
                    return false;
                }

                // if all running nodes are currently blocking forever on receive_data()
                if (node_id() == 0 && outstanding_messages == 0 && num_terminated_nodes + num_waiting_nodes == _cons.size())
                {
                    num_waiting_nodes = 0;
                    broadcast_byte(impl2::SEE_ALL_IN_WAITING_STATE);

                    // Note that the reason we have this epoch counter is so we can tell if a
                    // sent message is from before or after one of these "all nodes waiting"
                    // synchronization events.  If we didn't have the epoch count we would have
                    // a race condition where one node gets the SEE_ALL_IN_WAITING_STATE
                    // message before others and then sends out a message to another node
                    // before that node got the SEE_ALL_IN_WAITING_STATE message.  Then that
                    // node would think the normal message came before SEE_ALL_IN_WAITING_STATE
                    // which would be bad.
                    ++current_epoch;
                    return false;
                }

                impl1::msg_data data;
                if (!msg_buffer.pop(data, current_epoch))
                    throw dlib::socket_error("Error reading from msg_buffer in dlib::bsp_context.");

                switch(data.msg_type)
                {
                    case impl2::MESSAGE_HEADER: {
                        item = data.data;
                        sending_node_id = data.sender_id;
                        notify_control_node(impl2::GOT_MESSAGE);
                        return true;
                    } break;

                    case impl2::IN_WAITING_STATE: {
                        ++num_waiting_nodes;
                    } break;

                    case impl2::GOT_MESSAGE: {
                        --outstanding_messages;
                        --num_waiting_nodes;
                    } break;

                    case impl2::SENT_MESSAGE: {
                        ++outstanding_messages;
                    } break;

                    case impl2::NODE_TERMINATE: {
                        ++num_terminated_nodes;
                        _cons[data.sender_id]->terminated = true;
                    } break;

                    case impl2::SEE_ALL_IN_WAITING_STATE: {
                        ++current_epoch;
                        return false;
                    } break;

                    case impl2::READ_ERROR: {
                        throw dlib::socket_error(data.data_to_string());
                    } break;

                    default: {
                        throw dlib::socket_error("Unknown message received by dlib::bsp_context");
                    } break;
                } // end switch()
            } // end while (true)
        }

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

        void bsp_context::
        notify_control_node (
            char val
        )
        {
            if (node_id() == 0)
            {
                using namespace impl2;
                switch(val)
                {
                    case SENT_MESSAGE: {
                        ++outstanding_messages;
                    } break;

                    case GOT_MESSAGE: {
                        --outstanding_messages;
                    } break;

                    case IN_WAITING_STATE: {
                        // nothing to do in this case
                    } break;

                    default:
                        DLIB_CASSERT(false,"This should never happen");
                }
            }
            else
            {
                serialize(val, _cons[0]->stream);
                _cons[0]->stream.flush();
            }
        }

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

        void bsp_context::
        broadcast_byte (
            char val
        )
        {
            for (unsigned long i = 0; i < number_of_nodes(); ++i)
            {
                // don't send to yourself or to terminated nodes
                if (i == node_id() || _cons[i]->terminated)
                    continue;

                serialize(val, _cons[i]->stream);
                _cons[i]->stream.flush();
            }
        }

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

        void bsp_context::
        send_data(
            const std::vector<char>& item,
            unsigned long target_node_id
        )
        {
            using namespace impl2;
            if (_cons[target_node_id]->terminated)
                throw socket_error("Attempt to send a message to a node that has terminated.");

            serialize(MESSAGE_HEADER, _cons[target_node_id]->stream);
            serialize(current_epoch, _cons[target_node_id]->stream);
            serialize(item, _cons[target_node_id]->stream);
            _cons[target_node_id]->stream.flush();

            notify_control_node(SENT_MESSAGE);
        }

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

    }

    #endif // DLIB_BSP_CPph_