source: source/ariba/overlay/modules/chord/Chord.cpp

// [License]
// The Ariba-Underlay Copyright
//
// Copyright (c) 2008-2009, Institute of Telematics, UniversitÀt Karlsruhe (TH)
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// UniversitÀt Karlsruhe (TH)
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// Germany
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// [License]

#include "ariba/overlay/BaseOverlay.h"
#include "ariba/overlay/messages/OverlayMsg.h"

#include "Chord.h"
#include "detail/chord_routing_table.hpp"

//#include "messages/Discovery.h"  // XXX DEPRECATED

namespace ariba {
namespace overlay {

enum signalMessageTypes {
        typeDiscovery = OverlayMsg::typeSignalingStart + 0x01,
        typeLeave = OverlayMsg::typeSignalingStart + 0x02,
};

typedef chord_routing_table::item route_item;

using ariba::transport::system_priority;

use_logging_cpp( Chord );


////// Messages
struct DiscoveryMessage
{
    /**
     * DiscoveryMessage
     * - type
     * - data
     * - Endpoint
     */

    // type enum
    enum type_ {
        invalid = 0,
        normal = 1,
        successor = 2,
        predecessor = 3
    };

    
    // data
    uint8_t type;
    uint8_t ttl;
    EndpointDescriptor endpoint;

    // serialize
    reboost::message_t serialize()
    {
        // serialize endpoint
        reboost::message_t msg = endpoint.serialize();
        
        // serialize type and ttl
        uint8_t* buff1 = msg.push_front(2*sizeof(uint8_t)).mutable_data();
        buff1[0] = type;
        buff1[1] = ttl;
        
        return msg;
    }
    
    //deserialize
    reboost::shared_buffer_t deserialize(reboost::shared_buffer_t buff)
    {
        // deserialize type and ttl
        const uint8_t* bytes = buff.data();
        type = bytes[0];
        ttl = bytes[1];
        
        // deserialize endpoint
        return endpoint.deserialize(buff(2*sizeof(uint8_t)));
    }
};


Chord::Chord(BaseOverlay& _baseoverlay, const NodeID& _nodeid,
                OverlayStructureEvents* _eventsReceiver, const OverlayParameterSet& param) :
        OverlayInterface(_baseoverlay, _nodeid, _eventsReceiver, param) {

        // create routing table
        this->table = new chord_routing_table(_nodeid, 4);
        orphan_removal_counter = 0;
        discovery_count = 0;
        stabilize_counter = 0;
        stabilize_finger = 0;
}

Chord::~Chord() {

        // delete routing table
        delete table;
}

/// helper: sets up a link using the base overlay
LinkID Chord::setup(const EndpointDescriptor& endpoint, const NodeID& remote ) {

        // check if we already have a connection
        for (size_t i=0; i<table->size(); i++)
                if ((*table)[i]->ref_count > 0 && (*table)[i]->id == remote && !((*table)[i]->info.isUnspecified()))
                        return LinkID::UNSPECIFIED;

        // check if we are already trying to establish a link
        for (size_t i=0; i<pending.size(); i++)
                if ( pending[i] == remote ) {
                        logging_debug("Already trying to establish a link to node "
                                << remote.toString() );
                        return LinkID::UNSPECIFIED;
                }

        // adding node to list of pending connections
        pending.push_back( remote );

        logging_info("Request to setup link to " << endpoint.toString() );

        // establish link via base overlay
        return baseoverlay.establishLink( endpoint, remote,
                        OverlayInterface::OVERLAY_SERVICE_ID );
}

/// helper: sends a message using the "base overlay"
void Chord::send( OverlayMsg* msg, const LinkID& link ) {
        if (link.isUnspecified())
        return;
    
    try
    {
        baseoverlay.send_link( msg, link, system_priority::OVERLAY );
    }
    catch ( message_not_sent& e )
    {
        logging_warn("Chord: Could not send message over link " << link
                << ": " << e.what());
    }
}

void Chord::send_node( OverlayMsg* message, const NodeID& remote )
{
    try
    {
        baseoverlay.send( message, remote, system_priority::OVERLAY );
    }
    catch ( message_not_sent& e )
    {
        logging_warn("Chord: Could not send message to " << remote
                << ": " << e.what());
    }
}

/// sends a discovery message
void Chord::send_discovery_to(const NodeID& remote, int ttl) {
        LinkID link = getNextLinkId(remote);
        if ( remote == nodeid || link.isUnspecified()) return;
        if ( table->size() == 0 ) return;
        ttl = 2;

        OverlayMsg msg( typeDiscovery );
        msg.setRegisterRelay(true);
        
        // create DiscoveryMessage
        DiscoveryMessage dmsg;
        dmsg.type = DiscoveryMessage::normal;
        dmsg.ttl = ttl;
        dmsg.endpoint = baseoverlay.getEndpointDescriptor();

        msg.set_payload_message(dmsg.serialize());

        // send to node
    try
    {
        baseoverlay.send_node( &msg, remote, system_priority::OVERLAY );
    }
    catch ( message_not_sent& e )
    {
        logging_warn("Chord: Could not send message to " << remote
                << ": " << e.what());
    }
}

void Chord::discover_neighbors( const LinkID& link ) {
        uint8_t ttl = 1;
        
    // FIXME try-catch for the send operations
    
    // create DiscoveryMessage
    DiscoveryMessage dmsg;
    dmsg.ttl = ttl;
    dmsg.endpoint = baseoverlay.getEndpointDescriptor();
        {
                // send predecessor discovery
                OverlayMsg msg( typeDiscovery );
                msg.setRegisterRelay(true);

                // set type
            dmsg.type = DiscoveryMessage::predecessor;

            // send
            msg.set_payload_message(dmsg.serialize());
                send(&msg, link);
        }
        {
                // send successor discovery
                OverlayMsg msg( typeDiscovery );
//              msg.setSourceEndpoint( baseoverlay.getEndpointDescriptor() );  // XXX this was redundand, wasn't it?
                msg.setRegisterRelay(true);

                // set type
        dmsg.type = DiscoveryMessage::successor;

        // send
        msg.set_payload_message(dmsg.serialize());
                send(&msg, link);
        }
}


void Chord::createOverlay() {
}

void Chord::deleteOverlay() {

}

void Chord::joinOverlay(const EndpointDescriptor& boot) {
        logging_info( "joining Chord overlay structure through end-point " <<
                        (boot.isUnspecified() ? "local" : boot.toString()) );

        // initiator? no->setup first link
        if (!boot.isUnspecified())
                bootstrapLinks.push_back( setup(boot) );

        // timer for stabilization management
//      Timer::setInterval(1000);  // TODO find an appropriate interval!
        Timer::setInterval(10000);  // XXX testing...
        Timer::start();
}

void Chord::leaveOverlay() {
        Timer::stop();
        for (size_t i = 0; i < table->size(); i++) {
                route_item* it = (*table)[i];
                OverlayMsg msg( typeLeave );
                send( &msg, it->info );
        }
}

/// @see OverlayInterface.h
const EndpointDescriptor& Chord::resolveNode(const NodeID& node) {
        const route_item* item = table->get(node);
        if (item == NULL || item->info.isUnspecified()) return EndpointDescriptor::UNSPECIFIED();
        return baseoverlay.getEndpointDescriptor(item->info);
}

/// @see OverlayInterface.h
bool Chord::isClosestNodeTo( const NodeID& node ) {
        return table->is_closest_to(node);
}

/// @see OverlayInterface.h
const LinkID& Chord::getNextLinkId( const NodeID& id ) const {
        // get next hop
        const route_item* item = table->get_next_hop(id);

        // returns a unspecified id when this is itself
        if (item == NULL || item->id == nodeid)
                return LinkID::UNSPECIFIED;

        /// return routing info
        return item->info;
}

std::vector<const LinkID*> Chord::getSortedLinkIdsTowardsNode(
    const NodeID& id, int num ) const
{
    std::vector<const LinkID*> ret;
    
    switch ( num )
    {
        // special case: just call »getNextLinkId«
        case 1:
        {
            ret.push_back(&getNextLinkId(id));
            
            break;
        }
        
        // * calculate top 2 *
        case 0:
        case 2:
        {
            std::vector<const route_item*> items = table->get_next_2_hops(id);
            
            ret.reserve(items.size());
            
            BOOST_FOREACH( const route_item* item, items )
            {
                ret.push_back(&item->info);
            }
            
            break;
        }
        
        // NOTE: implement real sorting, if needed (and handle "case 0" properly, then)
        default:
        {
            throw std::runtime_error("Not implemented. (Chord::getSortedLinkIdsTowardsNode with num != 2)");
            
            break;
        }
    }
    
    return ret;
}


/// @see OverlayInterface.h
const NodeID& Chord::getNextNodeId( const NodeID& id ) const {
        // get next hop
        const route_item* item = table->get_next_hop(id);
        
        // return unspecified if no next hop could be found
        if (item == NULL) {
                return NodeID::UNSPECIFIED;
        }
        
        return item->id;
}

OverlayInterface::NodeList Chord::getKnownNodes(bool deep) const {
        OverlayInterface::NodeList nodelist;

        if( deep ){
                // all nodes that I know, fingers, succ/pred
                for (size_t i = 0; i < table->size(); i++){
                        if ((*table)[i]->ref_count != 0
                                        && !(*table)[i]->info.isUnspecified())
                                nodelist.push_back((*table)[i]->id);
                }
        } else {
                // only succ and pred
                if( table->get_predesessor() != NULL ){
                        nodelist.push_back( *(table->get_predesessor()) );
                }
                if( table->get_successor() != NULL ){
                        OverlayInterface::NodeList::iterator i =
                                std::find( nodelist.begin(), nodelist.end(), *(table->get_successor()) );
                        if( i == nodelist.end() )
                                nodelist.push_back( *(table->get_successor()) );
                }
        }

        return nodelist;
}

/// @see CommunicationListener.h
/// @see OverlayInterface.h
void Chord::onLinkUp(const LinkID& lnk, const NodeID& remote) {
        logging_info("link_up: link=" << lnk.toString() << " remote=" <<
                        remote.toString() );
        for (vector<NodeID>::iterator i=pending.begin(); i!=pending.end(); i++)
                if (*i == remote) {
                        pending.erase(i);
                        break;
                }

        if (remote==nodeid) {
                logging_warn("dropping link that has been established to myself (nodes have same nodeid?)");
                logging_warn("NodeID: " << remote);
                baseoverlay.dropLink(lnk);
                return;
        }

        route_item* item = table->insert(remote);

        // item added to routing table?
        if (item != NULL) { // yes-> add to routing table
                logging_info("new routing neighbor: " << remote.toString()
                                << " with link " << lnk.toString());

                // replace with new link if link is "better"
                if (item->info!=lnk && item->info.isUnspecified()==false) {
                        if (baseoverlay.compare( item->info, lnk ) == 1) {
                                logging_info("Replacing link due to concurrent link establishment.");
                                baseoverlay.dropLink(item->info);
                                item->info = lnk;
                        }
                } else {
                        item->info = lnk;
                }

                // discover neighbors of new overlay neighbor
                showLinks();
        } else { // no-> add orphan entry to routing table
                logging_info("new orphan: " << remote.toString()
                                << " with link " << lnk.toString());
                table->insert_orphan(remote)->info = lnk;
        }

        // erase bootstrap link
        vector<LinkID>::iterator it = std::find(bootstrapLinks.begin(), bootstrapLinks.end(), lnk);
        if( it != bootstrapLinks.end() ) bootstrapLinks.erase( it );
}

/// @see CommunicationListener.h or @see OverlayInterface.h
void Chord::onLinkDown(const LinkID& lnk, const NodeID& remote) {
    // XXX logging_debug
        logging_info("link_down (Chord): link=" << lnk.toString() << " remote=" <<
                        remote.toString() );

        // remove link from routing table
        route_item* item = table->get(remote);
        if (item!=NULL && item->info==lnk) {
                item->info = LinkID::UNSPECIFIED;
                table->remove(remote);
        }
}

/// @see CommunicationListener.h
/// @see OverlayInterface.h
void Chord::onMessage(OverlayMsg* msg,
        reboost::shared_buffer_t sub_msg,
        const NodeID& remote,
                const LinkID& link) {

        // handle messages
        switch ((signalMessageTypes) msg->getType()) {

        // discovery request
        case typeDiscovery:
        {
                // deserialize discovery message
                DiscoveryMessage dmsg;
                dmsg.deserialize(sub_msg);
                
                logging_debug("Received discovery message with"
                            << " src=" << msg->getSourceNode().toString()
                                << " dst=" << msg->getDestinationNode().toString()
                                << " ttl=" << (int)dmsg.ttl
                                << " type=" << (int)dmsg.type
                );

                // add discovery node id
                bool found = false;
                BOOST_FOREACH( NodeID& value, discovery )
                        if (value == msg->getSourceNode()) {
                                found = true;
                                break;
                        }
                if (!found) discovery.push_back(msg->getSourceNode());

                // check if source node can be added to routing table and setup link
                if (msg->getSourceNode() != nodeid)
                        setup( dmsg.endpoint, msg->getSourceNode() );

                // process discovery message -------------------------- switch start --
                switch ( dmsg.type )
                {
            // normal: route discovery message like every other message
            case DiscoveryMessage::normal:
            {
                // closest node? yes-> split to follow successor and predecessor
                if ( table->is_closest_to(msg->getDestinationNode()) )
                {
                    logging_debug("Discovery split:");
                    if (!table->get_successor()->isUnspecified())
                    {
                        OverlayMsg omsg(*msg);
                        
                        dmsg.type = DiscoveryMessage::successor;
                        omsg.set_payload_message(dmsg.serialize());

                        logging_debug("* Routing to successor "
                                << table->get_successor()->toString() );
                        send_node( &omsg, *table->get_successor() );
                    }
    
                    // send predecessor message
                    if (!table->get_predesessor()->isUnspecified())
                    {
                        OverlayMsg omsg(*msg);
                        
                        dmsg.type = DiscoveryMessage::predecessor;
                        omsg.set_payload_message(dmsg.serialize());

                        logging_debug("* Routing to predecessor "
                                << table->get_predesessor()->toString() );
                        send_node( &omsg, *table->get_predesessor() );
                    }
                }
                // no-> route message
                else
                {
                    baseoverlay.route( msg );
                }
                break;
            }
    
            // successor mode: follow the successor until TTL is zero
            case DiscoveryMessage::successor:
            case DiscoveryMessage::predecessor:
            {
                // reached destination? no->forward!
                if (msg->getDestinationNode() != nodeid)
                {
                    OverlayMsg omsg(*msg);
                    omsg.setService(OverlayInterface::OVERLAY_SERVICE_ID);
                    
                    omsg.set_payload_message(dmsg.serialize());
                    
                    baseoverlay.route( &omsg );
                    break;
                }
    
                // time to live ended? yes-> stop routing
                if (dmsg.ttl == 0 || dmsg.ttl > 10) break;
    
                // decrease time-to-live
                dmsg.ttl--;
    
                const route_item* item = NULL;
                if (dmsg.type == DiscoveryMessage::successor &&
                        table->get_successor() != NULL)
                {
                    item = table->get(*table->get_successor());
                }
                else if (table->get_predesessor() != NULL)
                {
                        item = table->get(*table->get_predesessor());
                }
                if (item == NULL)
                    break;
    
                logging_debug("Routing discovery message to succ/pred "
                    << item->id.toString() );
                OverlayMsg omsg(*msg);
                omsg.setService(OverlayInterface::OVERLAY_SERVICE_ID);
                omsg.setDestinationNode(item->id);
                
                omsg.set_payload_message(dmsg.serialize());
                
                send_node( &omsg, omsg.getDestinationNode() );
                break;
            }
            case DiscoveryMessage::invalid:
                break;
    
            default:
                break;
            }
            // process discovery message ---------------------------- switch end --
    
            break;
        }
    
        // leave
        case typeLeave: {
            if (link!=LinkID::UNSPECIFIED) {
                route_item* item = table->get(remote);
                if (item!=NULL) item->info = LinkID::UNSPECIFIED;
                table->remove(remote);
                baseoverlay.dropLink(link);
            }
            break;
        }
        }
}

void Chord::eventFunction() {
        stabilize_counter++;
        if (stabilize_counter < 0 || stabilize_counter == 2) {

                // reset counter
                stabilize_counter = 0;

                // clear pending connections
                pending.clear();

                // get number of real neighbors
                size_t numNeighbors = 0;
                for (size_t i = 0; i < table->size(); i++) {
                        route_item* it = (*table)[i];
                        if (it->ref_count != 0 && !it->info.isUnspecified()) numNeighbors++;
                }
                logging_info("Running stabilization: #links="
                                << table->size() << " #neighbors=" << numNeighbors );

                // updating neighbors
                logging_debug("Discover new ring neighbors");
                for (size_t i=0; i<table->size(); i++) {
                        LinkID id = (*table)[i]->info;
                        if (!id.isUnspecified()) discover_neighbors(id);
                }

                // sending discovery
                logging_debug("Sending discovery message to my neighbors and fingers");
                stabilize_finger = ((stabilize_finger+1) % table->get_finger_table_size() );
                const NodeID disc = table->get_finger_table(stabilize_finger).get_compare().get_center();
                if (disc != nodeid)
                        send_discovery_to(disc);

                // remove orphan links
                orphan_removal_counter++;
                if (orphan_removal_counter <0 || orphan_removal_counter >= 2) {
                        logging_info("Discovered nodes: ");
                        BOOST_FOREACH( NodeID& id, discovery )
                                logging_info("* " << id.toString());
                        discovery.clear();
                        logging_info("Running orphan removal");
                        orphan_removal_counter = 0;
                        for (size_t i = 0; i < table->size(); i++) {
                                route_item* it = (*table)[i];
                                if (it->ref_count == 0 && !it->info.isUnspecified()) {
                                        logging_info("Dropping orphaned link " << it->info.toString() << " to " << it->id.toString());
                                        table->insert(it->id);
                                        if (it->ref_count==0) {
                                                LinkID id = it->info;
                                                it->info = LinkID::UNSPECIFIED;
                                                baseoverlay.dropLink(id);
                                        }
                                }
                        }
                }
        }
}

void Chord::showLinks() {
        logging_info("--- chord routing information ----------------------------------");
        logging_info("predecessor: " << (table->get_predesessor()==NULL? "<none>" :
                table->get_predesessor()->toString()) );
        logging_info("node_id    : " << nodeid.toString() );
        logging_info("successor  : " << (table->get_successor()==NULL? "<none>" :
                table->get_successor()->toString()));
        logging_info("----------------------------------------------------------------");
}

/// @see OverlayInterface.h
std::string Chord::debugInformation() const {
        std::ostringstream s;
        s << "protocol   : Chord" << endl;
        s << "node_id    : " << nodeid.toString() << endl;
        s << "predecessor: " << (table->get_predesessor()==NULL? "<none>" :
                table->get_predesessor()->toString()) << endl;
        s << "successor  : " << (table->get_successor()==NULL? "<none>" :
                table->get_successor()->toString()) << endl;
        s << "nodes: " << endl;
        for (size_t i = 0; i < table->size(); i++) {
                route_item* it = (*table)[i];
                if (it->ref_count != 0 && !it->info.isUnspecified()) {
                        s << it->id.toString().substr(0,6)
                          << " using " << it->info.toString().substr(0,6) << endl;
                }
        }
        return s.str();
}



}} // namespace ariba, overlay