聊聊apache gossip的ActiveGossiper

/**
 * The ActiveGossipThread sends information. Pick a random partner and send the membership list to that partner
 */
public abstract class AbstractActiveGossiper {

  protected static final Logger LOGGER = Logger.getLogger(AbstractActiveGossiper.class);

  protected final GossipManager gossipManager;
  protected final GossipCore gossipCore;
  private final Histogram sharedDataHistogram;
  private final Histogram sendPerNodeDataHistogram;
  private final Histogram sendMembershipHistogram;
  private final Random random;
  private final GossipSettings gossipSettings;

  public AbstractActiveGossiper(GossipManager gossipManager, GossipCore gossipCore, MetricRegistry registry) {
    this.gossipManager = gossipManager;
    this.gossipCore = gossipCore;
    sharedDataHistogram = registry.histogram(name(AbstractActiveGossiper.class, "sharedDataHistogram-time"));
    sendPerNodeDataHistogram = registry.histogram(name(AbstractActiveGossiper.class, "sendPerNodeDataHistogram-time"));
    sendMembershipHistogram = registry.histogram(name(AbstractActiveGossiper.class, "sendMembershipHistogram-time"));
    random = new Random();
    gossipSettings = gossipManager.getSettings();
  }

  public void init() {

  }

  public void shutdown() {

  }

  public final void sendShutdownMessage(LocalMember me, LocalMember target){
    if (target == null){
      return;
    }
    ShutdownMessage m = new ShutdownMessage();
    m.setNodeId(me.getId());
    m.setShutdownAtNanos(gossipManager.getClock().nanoTime());
    gossipCore.sendOneWay(m, target.getUri());
  }

  //......

  /**
   * Performs the sending of the membership list, after we have incremented our own heartbeat.
   */
  protected void sendMembershipList(LocalMember me, LocalMember member) {
    if (member == null){
      return;
    }
    long startTime = System.currentTimeMillis();
    me.setHeartbeat(System.nanoTime());
    UdpActiveGossipMessage message = new UdpActiveGossipMessage();
    message.setUriFrom(gossipManager.getMyself().getUri().toASCIIString());
    message.setUuid(UUID.randomUUID().toString());
    message.getMembers().add(convert(me));
    for (LocalMember other : gossipManager.getMembers().keySet()) {
      message.getMembers().add(convert(other));
    }
    Response r = gossipCore.send(message, member.getUri());
    if (r instanceof ActiveGossipOk){
      //maybe count metrics here
    } else {
      LOGGER.debug("Message " + message + " generated response " + r);
    }
    sendMembershipHistogram.update(System.currentTimeMillis() - startTime);
  }

  protected final Member convert(LocalMember member){
    Member gm = new Member();
    gm.setCluster(member.getClusterName());
    gm.setHeartbeat(member.getHeartbeat());
    gm.setUri(member.getUri().toASCIIString());
    gm.setId(member.getId());
    gm.setProperties(member.getProperties());
    return gm;
  }

  /**
   *
   * @param memberList
   *          An immutable list
   * @return The chosen LocalGossipMember to gossip with.
   */
  protected LocalMember selectPartner(List<LocalMember> memberList) {
    LocalMember member = null;
    if (memberList.size() > 0) {
      int randomNeighborIndex = random.nextInt(memberList.size());
      member = memberList.get(randomNeighborIndex);
    }
    return member;
  }
}

public class ActiveGossipMessageHandler implements MessageHandler {
  
  /**
   * @param gossipCore context.
   * @param gossipManager context.
   * @param base message reference.
   * @return boolean indicating success.
   */
  @Override
  public boolean invoke(GossipCore gossipCore, GossipManager gossipManager, Base base) {
    List<Member> remoteGossipMembers = new ArrayList<>();
    RemoteMember senderMember = null;
    UdpActiveGossipMessage activeGossipMessage = (UdpActiveGossipMessage) base;
    for (int i = 0; i < activeGossipMessage.getMembers().size(); i++) {
      URI u;
      try {
        u = new URI(activeGossipMessage.getMembers().get(i).getUri());
      } catch (URISyntaxException e) {
        GossipCore.LOGGER.debug("Gossip message with faulty URI", e);
        continue;
      }
      RemoteMember member = new RemoteMember(
              activeGossipMessage.getMembers().get(i).getCluster(),
              u,
              activeGossipMessage.getMembers().get(i).getId(),
              activeGossipMessage.getMembers().get(i).getHeartbeat(),
              activeGossipMessage.getMembers().get(i).getProperties());
      if (i == 0) {
        senderMember = member;
      }
      if (!(member.getClusterName().equals(gossipManager.getMyself().getClusterName()))) {
        UdpNotAMemberFault f = new UdpNotAMemberFault();
        f.setException("Not a member of this cluster " + i);
        f.setUriFrom(activeGossipMessage.getUriFrom());
        f.setUuid(activeGossipMessage.getUuid());
        GossipCore.LOGGER.warn(f);
        gossipCore.sendOneWay(f, member.getUri());
        continue;
      }
      remoteGossipMembers.add(member);
    }
    UdpActiveGossipOk o = new UdpActiveGossipOk();
    o.setUriFrom(activeGossipMessage.getUriFrom());
    o.setUuid(activeGossipMessage.getUuid());
    gossipCore.sendOneWay(o, senderMember.getUri());
    gossipCore.mergeLists(senderMember, remoteGossipMembers);
    return true;
  }
}

public class GossipCore implements GossipCoreConstants {

  class LatchAndBase {
    private final CountDownLatch latch;
    private volatile Base base;
    
    LatchAndBase(){
      latch = new CountDownLatch(1);
    }
    
  }
  public static final Logger LOGGER = Logger.getLogger(GossipCore.class);
  private final GossipManager gossipManager;
  private ConcurrentHashMap<String, LatchAndBase> requests;
  private final ConcurrentHashMap<String, ConcurrentHashMap<String, PerNodeDataMessage>> perNodeData;
  private final ConcurrentHashMap<String, SharedDataMessage> sharedData;
  private final Meter messageSerdeException;
  private final Meter transmissionException;
  private final Meter transmissionSuccess;
  private final DataEventManager eventManager;
  
  public GossipCore(GossipManager manager, MetricRegistry metrics){
    this.gossipManager = manager;
    requests = new ConcurrentHashMap<>();
    perNodeData = new ConcurrentHashMap<>();
    sharedData = new ConcurrentHashMap<>();
    eventManager = new DataEventManager(metrics);
    metrics.register(PER_NODE_DATA_SIZE, (Gauge<Integer>)() -> perNodeData.size());
    metrics.register(SHARED_DATA_SIZE, (Gauge<Integer>)() ->  sharedData.size());
    metrics.register(REQUEST_SIZE, (Gauge<Integer>)() ->  requests.size());
    messageSerdeException = metrics.meter(MESSAGE_SERDE_EXCEPTION);
    transmissionException = metrics.meter(MESSAGE_TRANSMISSION_EXCEPTION);
    transmissionSuccess = metrics.meter(MESSAGE_TRANSMISSION_SUCCESS);
  }

  public void receive(Base base) {
    if (!gossipManager.getMessageHandler().invoke(this, gossipManager, base)) {
      LOGGER.warn("received message can not be handled");
    }
  }

  /**
   * Sends a blocking message.
   * todo: move functionality to TransportManager layer.
   * @param message
   * @param uri
   * @throws RuntimeException if data can not be serialized or in transmission error
   */
  private void sendInternal(Base message, URI uri) {
    byte[] json_bytes;
    try {
      json_bytes = gossipManager.getProtocolManager().write(message);
    } catch (IOException e) {
      messageSerdeException.mark();
      throw new RuntimeException(e);
    }
    try {
      gossipManager.getTransportManager().send(uri, json_bytes);
      transmissionSuccess.mark();
    } catch (IOException e) {
      transmissionException.mark();
      throw new RuntimeException(e);
    }
  }

  public Response send(Base message, URI uri){
    if (LOGGER.isDebugEnabled()){
      LOGGER.debug("Sending " + message);
      LOGGER.debug("Current request queue " + requests);
    }

    final Trackable t;
    LatchAndBase latchAndBase = null;
    if (message instanceof Trackable){
      t = (Trackable) message;
      latchAndBase = new LatchAndBase();
      requests.put(t.getUuid() + "/" + t.getUriFrom(), latchAndBase);
    } else {
      t = null;
    }
    sendInternal(message, uri);
    if (latchAndBase == null){
      return null;
    }
    
    try {
      boolean complete = latchAndBase.latch.await(1, TimeUnit.SECONDS);
      if (complete){
        return (Response) latchAndBase.base;
      } else{
        return null;
      }
    } catch (InterruptedException e) {
      throw new RuntimeException(e);
    } finally {
      if (latchAndBase != null){
        requests.remove(t.getUuid() + "/" + t.getUriFrom());
      }
    }
  }

  /**
   * Sends a message across the network while blocking. Catches and ignores IOException in transmission. Used
   * when the protocol for the message is not to wait for a response
   * @param message the message to send
   * @param u the uri to send it to
   */
  public void sendOneWay(Base message, URI u) {
    try {
      sendInternal(message, u);
    } catch (RuntimeException ex) {
      LOGGER.debug("Send one way failed", ex);
    }
  }

  public void handleResponse(String k, Base v) {
    LatchAndBase latch = requests.get(k);
    latch.base = v;
    latch.latch.countDown();
  }

  /**
   * Merge lists from remote members and update heartbeats
   *
   * @param senderMember
   * @param remoteList
   *
   */
  public void mergeLists(RemoteMember senderMember, List<Member> remoteList) {
    if (LOGGER.isDebugEnabled()){
      debugState(senderMember, remoteList);
    }
    for (LocalMember i : gossipManager.getDeadMembers()) {
      if (i.getId().equals(senderMember.getId())) {
        LOGGER.debug(gossipManager.getMyself() + " contacted by dead member " + senderMember.getUri());
        i.recordHeartbeat(senderMember.getHeartbeat());
        i.setHeartbeat(senderMember.getHeartbeat());
        //TODO consider forcing an UP here
      }
    }
    for (Member remoteMember : remoteList) {
      if (remoteMember.getId().equals(gossipManager.getMyself().getId())) {
        continue;
      }
      LocalMember aNewMember = new LocalMember(remoteMember.getClusterName(),
      remoteMember.getUri(),
      remoteMember.getId(),
      remoteMember.getHeartbeat(),
      remoteMember.getProperties(),
      gossipManager.getSettings().getWindowSize(),
      gossipManager.getSettings().getMinimumSamples(),
      gossipManager.getSettings().getDistribution());
      aNewMember.recordHeartbeat(remoteMember.getHeartbeat());
      Object result = gossipManager.getMembers().putIfAbsent(aNewMember, GossipState.UP);
      if (result != null){
        for (Entry<LocalMember, GossipState> localMember : gossipManager.getMembers().entrySet()){
          if (localMember.getKey().getId().equals(remoteMember.getId())){
            localMember.getKey().recordHeartbeat(remoteMember.getHeartbeat());
            localMember.getKey().setHeartbeat(remoteMember.getHeartbeat());
            localMember.getKey().setProperties(remoteMember.getProperties());
          }
        }
      }
    }
    if (LOGGER.isDebugEnabled()){
      debugState(senderMember, remoteList);
    }
  }

  //......

}

public abstract class GossipManager {

  public static final Logger LOGGER = Logger.getLogger(GossipManager.class);
  
  // this mapper is used for ring and user-data persistence only. NOT messages.
  public static final ObjectMapper metdataObjectMapper = new ObjectMapper() {
    private static final long serialVersionUID = 1L;
  {
    enableDefaultTyping();
    configure(JsonGenerator.Feature.WRITE_NUMBERS_AS_STRINGS, false);
  }};

  private final ConcurrentSkipListMap<LocalMember, GossipState> members;
  private final LocalMember me;
  private final GossipSettings settings;
  private final AtomicBoolean gossipServiceRunning;
  
  private TransportManager transportManager;
  private ProtocolManager protocolManager;
  
  private final GossipCore gossipCore;
  private final DataReaper dataReaper;
  private final Clock clock;
  private final ScheduledExecutorService scheduledServiced;
  private final MetricRegistry registry;
  private final RingStatePersister ringState;
  private final UserDataPersister userDataState;
  private final GossipMemberStateRefresher memberStateRefresher;
  
  private final MessageHandler messageHandler;
  private final LockManager lockManager;

  public GossipManager(String cluster,
                       URI uri, String id, Map<String, String> properties, GossipSettings settings,
                       List<Member> gossipMembers, GossipListener listener, MetricRegistry registry,
                       MessageHandler messageHandler) {
    this.settings = settings;
    this.messageHandler = messageHandler;

    clock = new SystemClock();
    me = new LocalMember(cluster, uri, id, clock.nanoTime(), properties,
            settings.getWindowSize(), settings.getMinimumSamples(), settings.getDistribution());
    gossipCore = new GossipCore(this, registry);
    this.lockManager = new LockManager(this, settings.getLockManagerSettings(), registry);
    dataReaper = new DataReaper(gossipCore, clock);
    members = new ConcurrentSkipListMap<>();
    for (Member startupMember : gossipMembers) {
      if (!startupMember.equals(me)) {
        LocalMember member = new LocalMember(startupMember.getClusterName(),
                startupMember.getUri(), startupMember.getId(),
                clock.nanoTime(), startupMember.getProperties(), settings.getWindowSize(),
                settings.getMinimumSamples(), settings.getDistribution());
        //TODO should members start in down state?
        members.put(member, GossipState.DOWN);
      }
    }
    gossipServiceRunning = new AtomicBoolean(true);
    this.scheduledServiced = Executors.newScheduledThreadPool(1);
    this.registry = registry;
    this.ringState = new RingStatePersister(GossipManager.buildRingStatePath(this), this);
    this.userDataState = new UserDataPersister(
        gossipCore,
        GossipManager.buildPerNodeDataPath(this),
        GossipManager.buildSharedDataPath(this));
    this.memberStateRefresher = new GossipMemberStateRefresher(members, settings, listener, this::findPerNodeGossipData);
    readSavedRingState();
    readSavedDataState();
  }

  /**
   * Starts the client. Specifically, start the various cycles for this protocol. Start the gossip
   * thread and start the receiver thread.
   */
  public void init() {
    
    // protocol manager and transport managers are specified in settings.
    // construct them here via reflection.
    
    protocolManager = ReflectionUtils.constructWithReflection(
        settings.getProtocolManagerClass(),
        new Class<?>[] { GossipSettings.class, String.class, MetricRegistry.class },
        new Object[] { settings, me.getId(), this.getRegistry() }
    );
    
    transportManager = ReflectionUtils.constructWithReflection(
        settings.getTransportManagerClass(),
        new Class<?>[] { GossipManager.class, GossipCore.class},
        new Object[] { this, gossipCore }
    );
    
    // start processing gossip messages.
    transportManager.startEndpoint();
    transportManager.startActiveGossiper();
    
    dataReaper.init();
    if (settings.isPersistRingState()) {
      scheduledServiced.scheduleAtFixedRate(ringState, 60, 60, TimeUnit.SECONDS);
    }
    if (settings.isPersistDataState()) {
      scheduledServiced.scheduleAtFixedRate(userDataState, 60, 60, TimeUnit.SECONDS);
    }
    memberStateRefresher.init();
    LOGGER.debug("The GossipManager is started.");
  }

  /**
   * Shutdown the gossip service.
   */
  public void shutdown() {
    gossipServiceRunning.set(false);
    lockManager.shutdown();
    gossipCore.shutdown();
    transportManager.shutdown();
    dataReaper.close();
    memberStateRefresher.shutdown();
    scheduledServiced.shutdown();
    try {
      scheduledServiced.awaitTermination(1, TimeUnit.SECONDS);
    } catch (InterruptedException e) {
      LOGGER.error(e);
    }
    scheduledServiced.shutdownNow();
  }

  //......

}

public class GossipMemberStateRefresher {
  public static final Logger LOGGER = Logger.getLogger(GossipMemberStateRefresher.class);

  private final Map<LocalMember, GossipState> members;
  private final GossipSettings settings;
  private final List<GossipListener> listeners = new CopyOnWriteArrayList<>();
  private final Clock clock;
  private final BiFunction<String, String, PerNodeDataMessage> findPerNodeGossipData;
  private final ExecutorService listenerExecutor;
  private final ScheduledExecutorService scheduledExecutor;
  private final BlockingQueue<Runnable> workQueue;

  public GossipMemberStateRefresher(Map<LocalMember, GossipState> members, GossipSettings settings,
                                    GossipListener listener,
                                    BiFunction<String, String, PerNodeDataMessage> findPerNodeGossipData) {
    this.members = members;
    this.settings = settings;
    listeners.add(listener);
    this.findPerNodeGossipData = findPerNodeGossipData;
    clock = new SystemClock();
    workQueue = new ArrayBlockingQueue<>(1024);
    listenerExecutor = new ThreadPoolExecutor(1, 20, 1, TimeUnit.SECONDS, workQueue,
            new ThreadPoolExecutor.DiscardOldestPolicy());
    scheduledExecutor = Executors.newScheduledThreadPool(1);
  }

  public void init() {
    scheduledExecutor.scheduleAtFixedRate(() -> run(), 0, 100, TimeUnit.MILLISECONDS);
  }

  public void run() {
    try {
      runOnce();
    } catch (RuntimeException ex) {
      LOGGER.warn("scheduled state had exception", ex);
    }
  }

  public void runOnce() {
    for (Entry<LocalMember, GossipState> entry : members.entrySet()) {
      boolean userDown = processOptimisticShutdown(entry);
      if (userDown)
        continue;

      Double phiMeasure = entry.getKey().detect(clock.nanoTime());
      GossipState requiredState;

      if (phiMeasure != null) {
        requiredState = calcRequiredState(phiMeasure);
      } else {
        requiredState = calcRequiredStateCleanupInterval(entry.getKey(), entry.getValue());
      }

      if (entry.getValue() != requiredState) {
        members.put(entry.getKey(), requiredState);
        /* Call listeners asynchronously */
        for (GossipListener listener: listeners)
          listenerExecutor.execute(() -> listener.gossipEvent(entry.getKey(), requiredState));
      }
    }
  }

  public GossipState calcRequiredState(Double phiMeasure) {
    if (phiMeasure > settings.getConvictThreshold())
      return GossipState.DOWN;
    else
      return GossipState.UP;
  }

  public GossipState calcRequiredStateCleanupInterval(LocalMember member, GossipState state) {
    long now = clock.nanoTime();
    long nowInMillis = TimeUnit.MILLISECONDS.convert(now, TimeUnit.NANOSECONDS);
    if (nowInMillis - settings.getCleanupInterval() > member.getHeartbeat()) {
      return GossipState.DOWN;
    } else {
      return state;
    }
  }

  /**
   * If we have a special key the per-node data that means that the node has sent us
   * a pre-emptive shutdown message. We process this so node is seen down sooner
   *
   * @param l member to consider
   * @return true if node forced down
   */
  public boolean processOptimisticShutdown(Entry<LocalMember, GossipState> l) {
    PerNodeDataMessage m = findPerNodeGossipData.apply(l.getKey().getId(), ShutdownMessage.PER_NODE_KEY);
    if (m == null) {
      return false;
    }
    ShutdownMessage s = (ShutdownMessage) m.getPayload();
    if (s.getShutdownAtNanos() > l.getKey().getHeartbeat()) {
      members.put(l.getKey(), GossipState.DOWN);
      if (l.getValue() == GossipState.UP) {
        for (GossipListener listener: listeners)
          listenerExecutor.execute(() -> listener.gossipEvent(l.getKey(), GossipState.DOWN));
      }
      return true;
    }
    return false;
  }

  public void register(GossipListener listener) {
    listeners.add(listener);
  }

  public void shutdown() {
    scheduledExecutor.shutdown();
    try {
      scheduledExecutor.awaitTermination(5, TimeUnit.SECONDS);
    } catch (InterruptedException e) {
      LOGGER.debug("Issue during shutdown", e);
    }
    listenerExecutor.shutdown();
    try {
      listenerExecutor.awaitTermination(5, TimeUnit.SECONDS);
    } catch (InterruptedException e) {
      LOGGER.debug("Issue during shutdown", e);
    }
    listenerExecutor.shutdownNow();
  }
}

/**
 * Manage the protcol threads (active and passive gossipers).
 */
public abstract class AbstractTransportManager implements TransportManager {
  
  public static final Logger LOGGER = Logger.getLogger(AbstractTransportManager.class);
  
  private final ExecutorService gossipThreadExecutor;
  private final AbstractActiveGossiper activeGossipThread;
  protected final GossipManager gossipManager;
  protected final GossipCore gossipCore;
  
  public AbstractTransportManager(GossipManager gossipManager, GossipCore gossipCore) {
    this.gossipManager = gossipManager;
    this.gossipCore = gossipCore;
    gossipThreadExecutor = Executors.newCachedThreadPool();
    activeGossipThread = ReflectionUtils.constructWithReflection(
      gossipManager.getSettings().getActiveGossipClass(),
        new Class<?>[]{
            GossipManager.class, GossipCore.class, MetricRegistry.class
        },
        new Object[]{
            gossipManager, gossipCore, gossipManager.getRegistry()
        });
  }

  // shut down threads etc.
  @Override
  public void shutdown() {
    gossipThreadExecutor.shutdown();
    if (activeGossipThread != null) {
      activeGossipThread.shutdown();
    }
    try {
      boolean result = gossipThreadExecutor.awaitTermination(10, TimeUnit.MILLISECONDS);
      if (!result) {
        // common when blocking patterns are used to read data from a socket.
        LOGGER.warn("executor shutdown timed out");
      }
    } catch (InterruptedException e) {
      LOGGER.error(e);
    }
    gossipThreadExecutor.shutdownNow();
  }

  @Override
  public void startActiveGossiper() {
    activeGossipThread.init();
  }

  @Override
  public abstract void startEndpoint();
}

/**
 * Base implementation gossips randomly to live nodes periodically gossips to dead ones
 *
 */
public class SimpleActiveGossiper extends AbstractActiveGossiper {

  private ScheduledExecutorService scheduledExecutorService;
  private final BlockingQueue<Runnable> workQueue;
  private ThreadPoolExecutor threadService;
  
  public SimpleActiveGossiper(GossipManager gossipManager, GossipCore gossipCore,
                              MetricRegistry registry) {
    super(gossipManager, gossipCore, registry);
    scheduledExecutorService = Executors.newScheduledThreadPool(2);
    workQueue = new ArrayBlockingQueue<Runnable>(1024);
    threadService = new ThreadPoolExecutor(1, 30, 1, TimeUnit.SECONDS, workQueue,
            new ThreadPoolExecutor.DiscardOldestPolicy());
  }

  @Override
  public void init() {
    super.init();
    scheduledExecutorService.scheduleAtFixedRate(() -> {
      threadService.execute(() -> {
        sendToALiveMember();
      });
    }, 0, gossipManager.getSettings().getGossipInterval(), TimeUnit.MILLISECONDS);
    scheduledExecutorService.scheduleAtFixedRate(() -> {
      sendToDeadMember();
    }, 0, gossipManager.getSettings().getGossipInterval(), TimeUnit.MILLISECONDS);
    scheduledExecutorService.scheduleAtFixedRate(
            () -> sendPerNodeData(gossipManager.getMyself(),
                    selectPartner(gossipManager.getLiveMembers())),
            0, gossipManager.getSettings().getGossipInterval(), TimeUnit.MILLISECONDS);
    scheduledExecutorService.scheduleAtFixedRate(
            () -> sendSharedData(gossipManager.getMyself(),
                    selectPartner(gossipManager.getLiveMembers())),
            0, gossipManager.getSettings().getGossipInterval(), TimeUnit.MILLISECONDS);
  }
  
  @Override
  public void shutdown() {
    super.shutdown();
    scheduledExecutorService.shutdown();
    try {
      scheduledExecutorService.awaitTermination(5, TimeUnit.SECONDS);
    } catch (InterruptedException e) {
      LOGGER.debug("Issue during shutdown", e);
    }
    sendShutdownMessage();
    threadService.shutdown();
    try {
      threadService.awaitTermination(5, TimeUnit.SECONDS);
    } catch (InterruptedException e) {
      LOGGER.debug("Issue during shutdown", e);
    }
  }

  protected void sendToALiveMember(){
    LocalMember member = selectPartner(gossipManager.getLiveMembers());
    sendMembershipList(gossipManager.getMyself(), member);
  }
  
  protected void sendToDeadMember(){
    LocalMember member = selectPartner(gossipManager.getDeadMembers());
    sendMembershipList(gossipManager.getMyself(), member);
  }
  
  /**
   * sends an optimistic shutdown message to several clusters nodes
   */
  protected void sendShutdownMessage(){
    List<LocalMember> l = gossipManager.getLiveMembers();
    int sendTo = l.size() < 3 ? 1 : l.size() / 2;
    for (int i = 0; i < sendTo; i++) {
      threadService.execute(() -> sendShutdownMessage(gossipManager.getMyself(), selectPartner(l)));
    }
  }
}