/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * Modified by ScyllaDB
 * Copyright (C) 2015 ScyllaDB
 */

/*
 * This file is part of Scylla.
 *
 * Scylla is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Scylla is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Scylla.  If not, see <http://www.gnu.org/licenses/>.
 */

#include "gms/inet_address.hh"
#include "gms/endpoint_state.hh"
#include "gms/gossip_digest.hh"
#include "gms/gossip_digest_syn.hh"
#include "gms/gossip_digest_ack.hh"
#include "gms/gossip_digest_ack2.hh"
#include "gms/versioned_value.hh"
#include "gms/gossiper.hh"
#include "gms/feature_service.hh"
#include "gms/application_state.hh"
#include "gms/failure_detector.hh"
#include "gms/i_failure_detection_event_listener.hh"
#include "gms/i_endpoint_state_change_subscriber.hh"
#include "message/messaging_service.hh"
#include "database.hh"
#include "log.hh"
#include "db/system_keyspace.hh"
#include <seastar/core/sleep.hh>
#include <seastar/core/thread.hh>
#include <seastar/core/metrics.hh>
#include <seastar/util/defer.hh>
#include <chrono>
#include "db/config.hh"
#include <boost/range/algorithm/set_algorithm.hpp>
#include <boost/range/adaptors.hpp>
#include "utils/generation-number.hh"
#include "locator/token_metadata.hh"

namespace gms {

using clk = gossiper::clk;

static logging::logger logger("gossip");

constexpr std::chrono::milliseconds gossiper::INTERVAL;
constexpr std::chrono::hours gossiper::A_VERY_LONG_TIME;
constexpr int64_t gossiper::MAX_GENERATION_DIFFERENCE;

distributed<gossiper> _the_gossiper;

netw::msg_addr gossiper::get_msg_addr(inet_address to) const noexcept {
    return msg_addr{to, _default_cpuid};
}

const sstring& gossiper::get_cluster_name() const noexcept {
    return _cluster_name;
}

void gossiper::set_cluster_name(sstring name) {
    _cluster_name = name;
}

const sstring& gossiper::get_partitioner_name() const noexcept {
    return _cfg.partitioner();
}

const std::set<inet_address>& gossiper::get_seeds() const noexcept {
    return _seeds_from_config;
}

void gossiper::set_seeds(std::set<inet_address> seeds) {
    _seeds_from_config = std::move(seeds);
}

std::chrono::milliseconds gossiper::quarantine_delay() const noexcept {
    auto ring_delay = std::chrono::milliseconds(_cfg.ring_delay_ms());
    return ring_delay * 2;
}

class feature_enabler : public i_endpoint_state_change_subscriber {
    gossiper& _g;
public:
    feature_enabler(gossiper& g) : _g(g) {}
    void on_join(inet_address ep, endpoint_state state) override {
        _g.maybe_enable_features();
    }
    void on_change(inet_address ep, application_state state, const versioned_value&) override {
        if (state == application_state::SUPPORTED_FEATURES) {
            _g.maybe_enable_features();
        }
    }
    void before_change(inet_address, endpoint_state, application_state, const versioned_value&) override { }
    void on_alive(inet_address, endpoint_state) override {}
    void on_dead(inet_address, endpoint_state) override {}
    void on_remove(inet_address) override {}
    void on_restart(inet_address, endpoint_state) override {}
};

gossiper::gossiper(abort_source& as, feature_service& features, const locator::shared_token_metadata& stm, netw::messaging_service& ms, db::config& cfg, gossip_config gcfg)
        : _abort_source(as)
        , _feature_service(features)
        , _shared_token_metadata(stm)
        , _messaging(ms)
        , _cfg(cfg)
        , _gcfg(gcfg)
        , _fd(cfg.phi_convict_threshold(),
                std::chrono::milliseconds(cfg.fd_initial_value_ms()),
                std::chrono::milliseconds(cfg.fd_max_interval_ms())) {
    // Gossiper's stuff below runs only on CPU0
    if (this_shard_id() != 0) {
        return;
    }

    _scheduled_gossip_task.set_callback(_gcfg.gossip_scheduling_group, [this] { run(); });
    // half of QUARATINE_DELAY, to ensure _just_removed_endpoints has enough leeway to prevent re-gossip
    fat_client_timeout = quarantine_delay() / 2;
    /* register with the Failure Detector for receiving Failure detector events */
    fd().register_failure_detection_event_listener(this);
    register_(make_shared<feature_enabler>(*this));
    // Register this instance with JMX
    namespace sm = seastar::metrics;
    auto ep = get_broadcast_address();
    _metrics.add_group("gossip", {
        sm::make_derive("heart_beat",
            [ep, this] {
                auto es = get_endpoint_state_for_endpoint_ptr(ep);
                if (es) {
                    return es->get_heart_beat_state().get_heart_beat_version();
                } else {
                    return 0;
                }
            }, sm::description("Heartbeat of the current Node.")),
    });
}

/*
 * First construct a map whose key is the endpoint in the GossipDigest and the value is the
 * GossipDigest itself. Then build a list of version differences i.e difference between the
 * version in the GossipDigest and the version in the local state for a given InetAddress.
 * Sort this list. Now loop through the sorted list and retrieve the GossipDigest corresponding
 * to the endpoint from the map that was initially constructed.
*/
void gossiper::do_sort(utils::chunked_vector<gossip_digest>& g_digest_list) {
    /* Construct a map of endpoint to GossipDigest. */
    std::map<inet_address, gossip_digest> ep_to_digest_map;
    for (auto g_digest : g_digest_list) {
        ep_to_digest_map.emplace(g_digest.get_endpoint(), g_digest);
    }

    /*
     * These digests have their maxVersion set to the difference of the version
     * of the local EndpointState and the version found in the GossipDigest.
    */
    utils::chunked_vector<gossip_digest> diff_digests;
    for (auto g_digest : g_digest_list) {
        auto ep = g_digest.get_endpoint();
        auto* ep_state = this->get_endpoint_state_for_endpoint_ptr(ep);
        int version = ep_state ? this->get_max_endpoint_state_version(*ep_state) : 0;
        int diff_version = ::abs(version - g_digest.get_max_version());
        diff_digests.emplace_back(gossip_digest(ep, g_digest.get_generation(), diff_version));
    }

    g_digest_list.clear();
    std::sort(diff_digests.begin(), diff_digests.end());
    int size = diff_digests.size();
    /*
     * Report the digests in descending order. This takes care of the endpoints
     * that are far behind w.r.t this local endpoint
    */
    for (int i = size - 1; i >= 0; --i) {
        g_digest_list.emplace_back(ep_to_digest_map[diff_digests[i].get_endpoint()]);
    }
}

// Depends on
// - no external dependency
future<> gossiper::handle_syn_msg(msg_addr from, gossip_digest_syn syn_msg) {
    logger.trace("handle_syn_msg():from={},cluster_name:peer={},local={},partitioner_name:peer={},local={}",
        from, syn_msg.cluster_id(), get_cluster_name(), syn_msg.partioner(), get_partitioner_name());
    if (!this->is_enabled()) {
        return make_ready_future<>();
    }

    /* If the message is from a different cluster throw it away. */
    if (syn_msg.cluster_id() != get_cluster_name()) {
        logger.warn("ClusterName mismatch from {} {}!={}", from.addr, syn_msg.cluster_id(), get_cluster_name());
        return make_ready_future<>();
    }

    if (syn_msg.partioner() != "" && syn_msg.partioner() != get_partitioner_name()) {
        logger.warn("Partitioner mismatch from {} {}!={}", from.addr, syn_msg.partioner(), get_partitioner_name());
        return make_ready_future<>();
    }

    syn_msg_pending& p = _syn_handlers[from.addr];
    if (p.pending) {
        // The latest syn message from peer has the latest infomation, so
        // it is safe to drop the previous syn message and keep the latest
        // one only.
        logger.debug("Queue gossip syn msg from node {}, syn_msg={}", from, syn_msg);
        p.syn_msg = std::move(syn_msg);
        return make_ready_future<>();
    } else {
        // Process the syn message immediately
        logger.debug("Process gossip syn msg from node {}, syn_msg={}", from, syn_msg);
        p.pending = true;
        return do_with(std::move(syn_msg), [this, from, g = this->shared_from_this()] (gossip_digest_syn& syn_msg) mutable {
            return repeat([this, from, g, &syn_msg] {
                return do_send_ack_msg(from, std::move(syn_msg)).then([this, from, &syn_msg] () mutable {
                    if (!_syn_handlers.contains(from.addr)) {
                        return stop_iteration::yes;
                    }
                    syn_msg_pending& p = _syn_handlers[from.addr];
                    if (p.syn_msg) {
                        // Process pending gossip syn msg and send ack msg back
                        logger.debug("Handle queued gossip syn msg from node {}, syn_msg={}, pending={}",
                                from, p.syn_msg, p.pending);
                        syn_msg = std::move(p.syn_msg.value());
                        p.syn_msg = {};
                        return stop_iteration::no;
                    } else {
                        // No more pending syn msg to process
                        p.pending = false;
                        logger.debug("No more queued gossip syn msg from node {}, syn_msg={}, pending={}",
                                from, p.syn_msg, p.pending);
                        return stop_iteration::yes;
                    }
                }).handle_exception([this, from] (std::exception_ptr ep) {
                    if (_syn_handlers.contains(from.addr)) {
                        syn_msg_pending& p = _syn_handlers[from.addr];
                        p.pending = false;
                        p.syn_msg = {};
                    }
                    logger.warn("Failed to process gossip syn msg from node {}:  {}", from, ep);
                    return make_exception_future<stop_iteration>(ep);
                });
            });
        });
    }
}

future<> gossiper::do_send_ack_msg(msg_addr from, gossip_digest_syn syn_msg) {
    return futurize_invoke([this, from, syn_msg = std::move(syn_msg)] () mutable {
        auto g_digest_list = syn_msg.get_gossip_digests();
        do_sort(g_digest_list);
        utils::chunked_vector<gossip_digest> delta_gossip_digest_list;
        std::map<inet_address, endpoint_state> delta_ep_state_map;
        this->examine_gossiper(g_digest_list, delta_gossip_digest_list, delta_ep_state_map);
        gms::gossip_digest_ack ack_msg(std::move(delta_gossip_digest_list), std::move(delta_ep_state_map));
        logger.debug("Calling do_send_ack_msg to node {}, syn_msg={}, ack_msg={}", from, syn_msg, ack_msg);
        return _messaging.send_gossip_digest_ack(from, std::move(ack_msg));
    });
}

class gossiper::msg_proc_guard {
public:
    msg_proc_guard(gossiper& g)
                    : _ptr(&(++g._msg_processing), [](uint64_t * p) { if (p) { --(*p); } })
    {}
    msg_proc_guard(msg_proc_guard&& m) = default;
private:
    std::unique_ptr<uint64_t, void(*)(uint64_t*)> _ptr;
};

// Depends on
// - failure_detector
// - on_change callbacks, e.g., storage_service -> access db system_table
// - on_restart callbacks
// - on_join callbacks
// - on_alive
future<> gossiper::handle_ack_msg(msg_addr id, gossip_digest_ack ack_msg) {
    logger.trace("handle_ack_msg():from={},msg={}", id, ack_msg);

    if (!this->is_enabled() && !this->is_in_shadow_round()) {
        return make_ready_future<>();
    }

    msg_proc_guard mp(*this);

    auto g_digest_list = ack_msg.get_gossip_digest_list();
    auto& ep_state_map = ack_msg.get_endpoint_state_map();

    auto f = make_ready_future<>();
    if (ep_state_map.size() > 0) {
        /* Notify the Failure Detector */
        this->notify_failure_detector(ep_state_map);
        f = this->apply_state_locally(std::move(ep_state_map));
    }

    assert(_msg_processing > 0);

    return f.then([this, from = id, ack_msg_digest = std::move(g_digest_list), mp = std::move(mp), g = this->shared_from_this()] () mutable {
        if (this->is_in_shadow_round()) {
            this->finish_shadow_round();
            // don't bother doing anything else, we have what we came for
            return make_ready_future<>();
        }
        ack_msg_pending& p = _ack_handlers[from.addr];
        if (p.pending) {
            // The latest ack message digests from peer has the latest infomation, so
            // it is safe to drop the previous ack message digests and keep the latest
            // one only.
            logger.debug("Queue gossip ack msg digests from node {}, ack_msg_digest={}", from, ack_msg_digest);
            p.ack_msg_digest = std::move(ack_msg_digest);
            return make_ready_future<>();
        } else {
            // Process the ack message immediately
            logger.debug("Process gossip ack msg digests from node {}, ack_msg_digest={}", from, ack_msg_digest);
            p.pending = true;
            return do_with(std::move(ack_msg_digest), [this, from, g] (utils::chunked_vector<gossip_digest>& ack_msg_digest) mutable {
                return repeat([this, from, g, &ack_msg_digest] {
                    return do_send_ack2_msg(from, std::move(ack_msg_digest)).then([this, from, &ack_msg_digest] () mutable {
                        if (!_ack_handlers.contains(from.addr)) {
                            return stop_iteration::yes;
                        }
                        ack_msg_pending& p = _ack_handlers[from.addr];
                        if (p.ack_msg_digest) {
                            // Process pending gossip ack msg digests and send ack2 msg back
                            logger.debug("Handle queued gossip ack msg digests from node {}, ack_msg_digest={}, pending={}",
                                    from, p.ack_msg_digest, p.pending);
                            ack_msg_digest = std::move(p.ack_msg_digest.value());
                            p.ack_msg_digest= {};
                            return stop_iteration::no;
                        } else {
                            // No more pending ack msg digests to process
                            p.pending = false;
                            logger.debug("No more queued gossip ack msg digests from node {}, ack_msg_digest={}, pending={}",
                                    from, p.ack_msg_digest, p.pending);
                            return stop_iteration::yes;
                        }
                    }).handle_exception([this, from] (std::exception_ptr ep) {
                        if (_ack_handlers.contains(from.addr)) {
                            ack_msg_pending& p = _ack_handlers[from.addr];
                            p.pending = false;
                            p.ack_msg_digest = {};
                            logger.warn("Failed to process gossip ack msg digests from node {}: {}", from, ep);
                        }
                        return make_exception_future<stop_iteration>(ep);
                    });
                });
            });
        }
    });
}

future<> gossiper::do_send_ack2_msg(msg_addr from, utils::chunked_vector<gossip_digest> ack_msg_digest) {
    return futurize_invoke([this, from, ack_msg_digest = std::move(ack_msg_digest)] () mutable {
        /* Get the state required to send to this gossipee - construct GossipDigestAck2Message */
        std::map<inet_address, endpoint_state> delta_ep_state_map;
        for (auto g_digest : ack_msg_digest) {
            inet_address addr = g_digest.get_endpoint();
            auto local_ep_state_ptr = this->get_state_for_version_bigger_than(addr, g_digest.get_max_version());
            if (local_ep_state_ptr) {
                delta_ep_state_map.emplace(addr, *local_ep_state_ptr);
            }
        }
        gms::gossip_digest_ack2 ack2_msg(std::move(delta_ep_state_map));
        logger.debug("Calling do_send_ack2_msg to node {}, ack_msg_digest={}, ack2_msg={}", from, ack_msg_digest, ack2_msg);
        return _messaging.send_gossip_digest_ack2(from, std::move(ack2_msg));
    });
}

// Depends on
// - failure_detector
// - on_change callbacks, e.g., storage_service -> access db system_table
// - on_restart callbacks
// - on_join callbacks
// - on_alive callbacks
future<> gossiper::handle_ack2_msg(gossip_digest_ack2 msg) {
    logger.trace("handle_ack2_msg():msg={}", msg);
    if (!is_enabled()) {
        return make_ready_future<>();
    }

    msg_proc_guard mp(*this);

    auto& remote_ep_state_map = msg.get_endpoint_state_map();
    /* Notify the Failure Detector */
    notify_failure_detector(remote_ep_state_map);
    return apply_state_locally(std::move(remote_ep_state_map)).finally([mp = std::move(mp)] {});
}

future<> gossiper::handle_echo_msg() {
    return make_ready_future<>();
}

future<> gossiper::handle_shutdown_msg(inet_address from) {
    if (!is_enabled()) {
        logger.debug("Ignoring shutdown message from {} because gossip is disabled", from);
        return make_ready_future<>();
    }
    return seastar::async([this, from] {
        auto permit = this->lock_endpoint(from).get0();
        this->mark_as_shutdown(from);
    });
}

future<gossip_get_endpoint_states_response>
gossiper::handle_get_endpoint_states_msg(gossip_get_endpoint_states_request request) {
    std::unordered_map<gms::inet_address, gms::endpoint_state> map;
    const auto& application_states_wanted = request.application_states;
    for (auto& item : endpoint_state_map) {
        const inet_address& node = item.first;
        const endpoint_state& state = item.second;
        const heart_beat_state& hbs = state.get_heart_beat_state();
        auto state_wanted = endpoint_state(hbs);
        const std::map<application_state, versioned_value>& apps = state.get_application_state_map();
        for (const auto& app : apps) {
            if (application_states_wanted.count(app.first) > 0) {
                state_wanted.get_application_state_map().emplace(app);
            }
        }
        map.emplace(node, std::move(state_wanted));
    }
    return make_ready_future<gossip_get_endpoint_states_response>(gossip_get_endpoint_states_response{std::move(map)});
}

future<> gossiper::init_messaging_service_handler(bind_messaging_port do_bind) {
    if (_ms_registered) {
        return make_ready_future<>();
    }
    _ms_registered = true;
    _messaging.register_gossip_digest_syn([] (const rpc::client_info& cinfo, gossip_digest_syn syn_msg) {
        auto from = netw::messaging_service::get_source(cinfo);
        // In a new fiber.
        (void)smp::submit_to(0, [from, syn_msg = std::move(syn_msg)] () mutable {
            auto& gossiper = gms::get_local_gossiper();
            return gossiper.handle_syn_msg(from, std::move(syn_msg));
        }).handle_exception([] (auto ep) {
            logger.warn("Fail to handle GOSSIP_DIGEST_SYN: {}", ep);
        });
        return messaging_service::no_wait();
    });
    _messaging.register_gossip_digest_ack([] (const rpc::client_info& cinfo, gossip_digest_ack msg) {
        auto from = netw::messaging_service::get_source(cinfo);
        // In a new fiber.
        (void)smp::submit_to(0, [from, msg = std::move(msg)] () mutable {
            auto& gossiper = gms::get_local_gossiper();
            return gossiper.handle_ack_msg(from, std::move(msg));
        }).handle_exception([] (auto ep) {
            logger.warn("Fail to handle GOSSIP_DIGEST_ACK: {}", ep);
        });
        return messaging_service::no_wait();
    });
    _messaging.register_gossip_digest_ack2([] (gossip_digest_ack2 msg) {
        // In a new fiber.
        (void)smp::submit_to(0, [msg = std::move(msg)] () mutable {
            return gms::get_local_gossiper().handle_ack2_msg(std::move(msg));
        }).handle_exception([] (auto ep) {
            logger.warn("Fail to handle GOSSIP_DIGEST_ACK2: {}", ep);
        });
        return messaging_service::no_wait();
    });
    _messaging.register_gossip_echo([] {
        return gms::get_local_gossiper().handle_echo_msg();
    });
    _messaging.register_gossip_shutdown([] (inet_address from) {
        // In a new fiber.
        (void)smp::submit_to(0, [from] {
            return gms::get_local_gossiper().handle_shutdown_msg(from);
        }).handle_exception([] (auto ep) {
            logger.warn("Fail to handle GOSSIP_SHUTDOWN: {}", ep);
        });
        return messaging_service::no_wait();
    });
    _messaging.register_gossip_get_endpoint_states([] (const rpc::client_info& cinfo, gossip_get_endpoint_states_request request) {
        return smp::submit_to(0, [request = std::move(request)] () mutable {
            return gms::get_local_gossiper().handle_get_endpoint_states_msg(std::move(request));
        });
    });

    // Start listening messaging_service after gossip message handlers are registered
    if (do_bind) {
        return _messaging.start_listen();
    }
    return make_ready_future<>();
}

future<> gossiper::uninit_messaging_service_handler() {
    auto& ms = _messaging;
    return when_all_succeed(
        ms.unregister_gossip_echo(),
        ms.unregister_gossip_shutdown(),
        ms.unregister_gossip_digest_syn(),
        ms.unregister_gossip_digest_ack(),
        ms.unregister_gossip_digest_ack2(),
        ms.unregister_gossip_get_endpoint_states()
    ).then_unpack([this] {
        _ms_registered = false;
    });
}

future<> gossiper::send_gossip(gossip_digest_syn message, std::set<inet_address> epset) {
    utils::chunked_vector<inet_address> __live_endpoints(epset.begin(), epset.end());
    size_t size = __live_endpoints.size();
    if (size < 1) {
        return make_ready_future<>();
    }
    /* Generate a random number from 0 -> size */
    std::uniform_int_distribution<int> dist(0, size - 1);
    int index = dist(_random_engine);
    inet_address to = __live_endpoints[index];
    auto id = get_msg_addr(to);
    logger.trace("Sending a GossipDigestSyn to {} ...", id);
    return _messaging.send_gossip_digest_syn(id, std::move(message)).handle_exception([id] (auto ep) {
        // It is normal to reach here because it is normal that a node
        // tries to send a SYN message to a peer node which is down before
        // failure_detector thinks that peer node is down.
        logger.trace("Fail to send GossipDigestSyn to {}: {}", id, ep);
    });
}


void gossiper::notify_failure_detector(inet_address endpoint, const endpoint_state& remote_endpoint_state) {
    /*
     * If the local endpoint state exists then report to the FD only
     * if the versions workout.
    */
    auto* local_endpoint_state = get_endpoint_state_for_endpoint_ptr(endpoint);
    if (local_endpoint_state) {
        int local_generation = local_endpoint_state->get_heart_beat_state().get_generation();
        int remote_generation = remote_endpoint_state.get_heart_beat_state().get_generation();
        if (remote_generation > local_generation) {
            local_endpoint_state->update_timestamp();
            // this node was dead and the generation changed, this indicates a reboot, or possibly a takeover
            // we will clean the fd intervals for it and relearn them
            if (!local_endpoint_state->is_alive()) {
                logger.debug("Clearing interval times for {} due to generation change", endpoint);
                fd().remove(endpoint);
            }
            fd().report(endpoint);
            return;
        }

        if (remote_generation == local_generation) {
            int local_version = get_max_endpoint_state_version(*local_endpoint_state);
            int remote_version = remote_endpoint_state.get_heart_beat_state().get_heart_beat_version();
            if (remote_version > local_version) {
                local_endpoint_state->update_timestamp();
                // just a version change, report to the fd
                fd().report(endpoint);
            }
        }
    }
}

// Runs inside seastar::async context
void gossiper::do_apply_state_locally(gms::inet_address node, const endpoint_state& remote_state, bool listener_notification) {
    // If state does not exist just add it. If it does then add it if the remote generation is greater.
    // If there is a generation tie, attempt to break it by heartbeat version.
    auto permit = this->lock_endpoint(node).get0();
    auto es = this->get_endpoint_state_for_endpoint_ptr(node);
    if (es) {
        endpoint_state& local_state = *es;
        int local_generation = local_state.get_heart_beat_state().get_generation();
        int remote_generation = remote_state.get_heart_beat_state().get_generation();
        logger.trace("{} local generation {}, remote generation {}", node, local_generation, remote_generation);
        if (remote_generation > utils::get_generation_number() + MAX_GENERATION_DIFFERENCE) {
            // assume some peer has corrupted memory and is broadcasting an unbelievable generation about another peer (or itself)
            logger.warn("received an invalid gossip generation for peer {}; local generation = {}, received generation = {}",
                node, local_generation, remote_generation);
        } else if (remote_generation > local_generation) {
            if (listener_notification) {
                logger.trace("Updating heartbeat state generation to {} from {} for {}", remote_generation, local_generation, node);
                // major state change will handle the update by inserting the remote state directly
                this->handle_major_state_change(node, remote_state);
            } else {
                logger.debug("Applying remote_state for node {} (remote generation > local generation)", node);
                endpoint_state_map[node] = remote_state;
            }
        } else if (remote_generation == local_generation) {
            if (listener_notification) {
                // find maximum state
                int local_max_version = this->get_max_endpoint_state_version(local_state);
                int remote_max_version = this->get_max_endpoint_state_version(remote_state);
                if (remote_max_version > local_max_version) {
                    // apply states, but do not notify since there is no major change
                    this->apply_new_states(node, local_state, remote_state);
                } else {
                    logger.trace("Ignoring remote version {} <= {} for {}", remote_max_version, local_max_version, node);
                }
                if (!local_state.is_alive() && !this->is_dead_state(local_state)) { // unless of course, it was dead
                    this->mark_alive(node, local_state);
                }
            } else {
                for (const auto& item : remote_state.get_application_state_map()) {
                    const auto& remote_key = item.first;
                    const auto& remote_value = item.second;
                    const versioned_value* local_value = local_state.get_application_state_ptr(remote_key);
                    if (!local_value || remote_value.version > local_value->version) {
                        logger.debug("Applying remote_state for node {} (remote generation = local generation), key={}, value={}",
                                node, remote_key, remote_value);
                        local_state.add_application_state(remote_key, remote_value);
                    } else {
                        logger.debug("Ignoring remote_state for node {} (remote generation = local generation), key={}, value={}", node, remote_key, remote_value);
                    }
                }
            }
        } else {
            logger.debug("Ignoring remote generation {} < {}", remote_generation, local_generation);
        }
    } else {
        if (listener_notification) {
            // this is a new node, report it to the FD in case it is the first time we are seeing it AND it's not alive
            fd().report(node);
            this->handle_major_state_change(node, remote_state);
        } else {
            logger.debug("Applying remote_state for node {} (new node)", node);
            endpoint_state_map[node] = remote_state;
        }
    }
}

// Runs inside seastar::async context
void gossiper::apply_state_locally_without_listener_notification(std::unordered_map<inet_address, endpoint_state> map) {
    for (auto& x : map) {
        const inet_address& node = x.first;
        const endpoint_state& remote_state = x.second;
        do_apply_state_locally(node, remote_state, false);
    }
}

future<> gossiper::apply_state_locally(std::map<inet_address, endpoint_state> map) {
    auto start = std::chrono::steady_clock::now();
    auto endpoints = boost::copy_range<utils::chunked_vector<inet_address>>(map | boost::adaptors::map_keys);
    std::shuffle(endpoints.begin(), endpoints.end(), _random_engine);
    auto node_is_seed = [this] (gms::inet_address ip) { return is_seed(ip); };
    boost::partition(endpoints, node_is_seed);
    logger.debug("apply_state_locally_endpoints={}", endpoints);

    return do_with(std::move(endpoints), std::move(map), [this] (auto&& endpoints, auto&& map) {
        return parallel_for_each(endpoints, [this, &map] (auto&& ep) -> future<> {
            if (ep == this->get_broadcast_address() && !this->is_in_shadow_round()) {
                return make_ready_future<>();
            }
            if (_just_removed_endpoints.contains(ep)) {
                logger.trace("Ignoring gossip for {} because it is quarantined", ep);
                return make_ready_future<>();
            }
          return seastar::with_semaphore(_apply_state_locally_semaphore, 1, [this, &ep, &map] () mutable {
            return seastar::async([this, &ep, &map] () mutable {
                do_apply_state_locally(ep, map[ep], true);
            });
          });
        });
    }).then([start] {
            logger.debug("apply_state_locally() took {} ms", std::chrono::duration_cast<std::chrono::milliseconds>(
                std::chrono::steady_clock::now() - start).count());
    });
}

future<> gossiper::force_remove_endpoint(inet_address endpoint) {
    if (endpoint == get_broadcast_address()) {
        return make_exception_future<>(std::runtime_error(format("Can not force remove node {} itself", endpoint)));
    }
    return get_gossiper().invoke_on(0, [endpoint] (auto& gossiper) mutable {
        return seastar::async([&gossiper, g = gossiper.shared_from_this(), endpoint] () mutable {
            gossiper.remove_endpoint(endpoint);
            gossiper.evict_from_membership(endpoint);
            logger.info("Finished to force remove node {}", endpoint);
        }).handle_exception([endpoint] (auto ep) {
            logger.warn("Failed to force remove node {}: {}", endpoint, ep);
        });
    });
}

// Runs inside seastar::async context
void gossiper::remove_endpoint(inet_address endpoint) {
    // do subscribers first so anything in the subscriber that depends on gossiper state won't get confused
    // We can not run on_remove callbacks here becasue on_remove in
    // storage_service might take the gossiper::timer_callback_lock
    (void)seastar::async([this, endpoint] {
        _subscribers.for_each([endpoint] (shared_ptr<i_endpoint_state_change_subscriber> subscriber) {
            subscriber->on_remove(endpoint);
        });
    }).handle_exception([] (auto ep) {
        logger.warn("Fail to call on_remove callback: {}", ep);
    });

    if(_seeds.contains(endpoint)) {
        build_seeds_list();
        _seeds.erase(endpoint);
        logger.info("removed {} from _seeds, updated _seeds list = {}", endpoint, _seeds);
    }

    _live_endpoints.resize(std::distance(_live_endpoints.begin(), std::remove(_live_endpoints.begin(), _live_endpoints.end(), endpoint)));
    _unreachable_endpoints.erase(endpoint);
    _syn_handlers.erase(endpoint);
    _ack_handlers.erase(endpoint);
    quarantine_endpoint(endpoint);
    logger.debug("removing endpoint {}", endpoint);
}

// Runs inside seastar::async context
void gossiper::do_status_check() {
    logger.trace("Performing status check ...");

    auto now = this->now();

    for (auto it = endpoint_state_map.begin(); it != endpoint_state_map.end();) {
        auto endpoint = it->first;
        auto& ep_state = it->second;
        it++;

        bool is_alive = ep_state.is_alive();
        if (endpoint == get_broadcast_address()) {
            continue;
        }

        fd().interpret(endpoint);

        // check if this is a fat client. fat clients are removed automatically from
        // gossip after FatClientTimeout.  Do not remove dead states here.
        if (is_gossip_only_member(endpoint)
            && !_just_removed_endpoints.contains(endpoint)
            && ((now - ep_state.get_update_timestamp()) > fat_client_timeout)) {
            logger.info("FatClient {} has been silent for {}ms, removing from gossip", endpoint, fat_client_timeout.count());
            remove_endpoint(endpoint); // will put it in _just_removed_endpoints to respect quarantine delay
            evict_from_membership(endpoint); // can get rid of the state immediately
        }

        // check for dead state removal
        auto expire_time = get_expire_time_for_endpoint(endpoint);
        if (!is_alive && (now > expire_time)
             && (!get_token_metadata_ptr()->is_member(endpoint))) {
            logger.debug("time is expiring for endpoint : {} ({})", endpoint, expire_time.time_since_epoch().count());
            evict_from_membership(endpoint);
        }
    }

    for (auto it = _just_removed_endpoints.begin(); it != _just_removed_endpoints.end();) {
        auto& t= it->second;
        if ((now - t) > quarantine_delay()) {
            logger.debug("{} ms elapsed, {} gossip quarantine over", quarantine_delay().count(), it->first);
            it = _just_removed_endpoints.erase(it);
        } else {
            it++;
        }
    }
}

future<gossiper::endpoint_permit> gossiper::lock_endpoint(inet_address ep) {
    return endpoint_locks.get_or_load(ep, [] (const inet_address& ep) { return semaphore(1); }).then([] (auto eptr) {
        return get_units(*eptr, 1).then([eptr] (auto units) mutable {
            return endpoint_permit{std::move(eptr), std::move(units)};
        });
    });
}

// Depends on:
// - failure_detector
// - on_remove callbacks, e.g, storage_service -> access token_metadata
void gossiper::run() {
   // Run it in the background.
  (void)seastar::with_semaphore(_callback_running, 1, [this] {
    return seastar::async([this, g = this->shared_from_this()] {
            logger.trace("=== Gossip round START");

            //wait on messaging service to start listening
            // MessagingService.instance().waitUntilListening();

            /* Update the local heartbeat counter. */
            auto br_addr = get_broadcast_address();
            heart_beat_state& hbs = endpoint_state_map[br_addr].get_heart_beat_state();
            hbs.update_heart_beat();

            logger.trace("My heartbeat is now {}", endpoint_state_map[br_addr].get_heart_beat_state().get_heart_beat_version());
            utils::chunked_vector<gossip_digest> g_digests;
            this->make_random_gossip_digest(g_digests);

            if (g_digests.size() > 0) {
                gossip_digest_syn message(get_cluster_name(), get_partitioner_name(), g_digests);

                if (_endpoints_to_talk_with.empty()) {
                    std::shuffle(_live_endpoints.begin(), _live_endpoints.end(), _random_engine);
                    // This guarantees the local node will talk with all nodes
                    // in live_endpoints at least once within nr_rounds gossip rounds.
                    // Other gossip implementation like SWIM uses similar approach.
                    // https://www.cs.cornell.edu/projects/Quicksilver/public_pdfs/SWIM.pdf
                    size_t nr_rounds = 10;
                    size_t nodes_per_round = (_live_endpoints.size() + nr_rounds - 1) / nr_rounds;
                    std::vector<inet_address> live_nodes;
                    for (const auto& node : _live_endpoints) {
                        if (live_nodes.size() < nodes_per_round) {
                            live_nodes.push_back(node);
                        } else {
                            _endpoints_to_talk_with.push_back(std::move(live_nodes));
                            live_nodes = {node};
                        }
                    }
                    if (!live_nodes.empty()) {
                        _endpoints_to_talk_with.push_back(live_nodes);
                    }
                    logger.debug("Set live nodes to talk: endpoint_state_map={}, all_live_nodes={}, endpoints_to_talk_with={}",
                            endpoint_state_map.size(), _live_endpoints, _endpoints_to_talk_with);
                }
                if (_endpoints_to_talk_with.empty()) {
                    auto nodes = std::vector<inet_address>(_seeds.begin(), _seeds.end());
                    logger.debug("No live nodes yet: try initial contact point nodes={}", nodes);
                    if (!nodes.empty()) {
                        _endpoints_to_talk_with.push_back(std::move(nodes));
                    }
                }
                if (!_endpoints_to_talk_with.empty()) {
                    auto live_nodes = _endpoints_to_talk_with.front();
                    _endpoints_to_talk_with.pop_front();
                    logger.debug("Talk to live nodes: {}", live_nodes);
                    for (auto& ep: live_nodes) {
                        // Do it in the background.
                        (void)do_gossip_to_live_member(message, ep).handle_exception([] (auto ep) {
                            logger.trace("Failed to do_gossip_to_live_member: {}", ep);
                        });
                    }
                } else {
                    logger.debug("No one to talk with");
                }

                /* Gossip to some unreachable member with some probability to check if he is back up */
                // Do it in the background.
                (void)do_gossip_to_unreachable_member(message).handle_exception([] (auto ep) {
                    logger.trace("Faill to do_gossip_to_unreachable_member: {}", ep);
                });

                do_status_check();
            }

            //
            // Gossiper task runs only on CPU0:
            //
            //    - If endpoint_state_map or _live_endpoints have changed - duplicate
            //      them across all other shards.
            //    - Reschedule the gossiper only after execution on all nodes is done.
            //
            bool live_endpoint_changed = (_live_endpoints != _shadow_live_endpoints);
            bool unreachable_endpoint_changed = (_unreachable_endpoints != _shadow_unreachable_endpoints);

            if (live_endpoint_changed || unreachable_endpoint_changed) {
                if (live_endpoint_changed) {
                    _shadow_live_endpoints = _live_endpoints;
                }

                if (unreachable_endpoint_changed) {
                    _shadow_unreachable_endpoints = _unreachable_endpoints;
                }

                _the_gossiper.invoke_on_all([this, live_endpoint_changed, unreachable_endpoint_changed, es = endpoint_state_map] (gossiper& local_gossiper) {
                    // Don't copy gossiper(CPU0) maps into themselves!
                    if (this_shard_id() != 0) {
                        if (live_endpoint_changed) {
                            local_gossiper._live_endpoints = _shadow_live_endpoints;
                        }

                        if (unreachable_endpoint_changed) {
                            local_gossiper._unreachable_endpoints = _shadow_unreachable_endpoints;
                        }

                        for (auto&& e : es) {
                            local_gossiper.endpoint_state_map[e.first].set_alive(e.second.is_alive());
                        }
                    }
                }).get();
            }
    }).then_wrapped([this] (auto&& f) {
        try {
            f.get();
            _nr_run++;
            logger.trace("=== Gossip round OK");
        } catch (...) {
            logger.warn("=== Gossip round FAIL: {}", std::current_exception());
        }

        if (logger.is_enabled(logging::log_level::trace)) {
            for (auto& x : endpoint_state_map) {
                logger.trace("ep={}, eps={}", x.first, x.second);
            }
        }
        if (_enabled) {
            _scheduled_gossip_task.arm(INTERVAL);
        } else {
            logger.info("Gossip loop is not scheduled because it is disabled");
        }
    });
  });
}

void gossiper::check_seen_seeds() {
    auto seen = std::any_of(endpoint_state_map.begin(), endpoint_state_map.end(), [this] (auto& entry) {
        if (_seeds.contains(entry.first)) {
            return true;
        }
        auto* internal_ip = entry.second.get_application_state_ptr(application_state::INTERNAL_IP);
        return internal_ip && _seeds.contains(inet_address(internal_ip->value));
    });
    logger.info("Known endpoints={}, current_seeds={}, seeds_from_config={}, seen_any_seed={}",
        boost::copy_range<std::list<inet_address>>(endpoint_state_map | boost::adaptors::map_keys),
        _seeds, _seeds_from_config, seen);
    if (!seen) {
        dump_endpoint_state_map();
        throw std::runtime_error("Unable to contact any seeds!");
    }
}

bool gossiper::is_seed(const gms::inet_address& endpoint) const {
    return _seeds.contains(endpoint);
}

void gossiper::register_(shared_ptr<i_endpoint_state_change_subscriber> subscriber) {
    _subscribers.add(subscriber);
}

future<> gossiper::unregister_(shared_ptr<i_endpoint_state_change_subscriber> subscriber) {
    return _subscribers.remove(subscriber);
}

std::set<inet_address> gossiper::get_live_members() {
    std::set<inet_address> live_members(_live_endpoints.begin(), _live_endpoints.end());
    auto myip = get_broadcast_address();
    logger.debug("live_members before={}", live_members);
    live_members.insert(myip);
    if (is_shutdown(myip)) {
        live_members.erase(myip);
    }
    logger.debug("live_members after={}", live_members);
    return live_members;
}

std::set<inet_address> gossiper::get_live_token_owners() {
    std::set<inet_address> token_owners;
    for (auto& member : get_live_members()) {
        auto es = get_endpoint_state_for_endpoint_ptr(member);
        if (es && !is_dead_state(*es) && get_token_metadata_ptr()->is_member(member)) {
            token_owners.insert(member);
        }
    }
    return token_owners;
}

std::set<inet_address> gossiper::get_unreachable_token_owners() {
    std::set<inet_address> token_owners;
    for (auto&& x : _unreachable_endpoints) {
        auto& endpoint = x.first;
        if (get_token_metadata_ptr()->is_member(endpoint)) {
            token_owners.insert(endpoint);
        }
    }
    return token_owners;
}

// Return downtime in microseconds
int64_t gossiper::get_endpoint_downtime(inet_address ep) const noexcept {
    auto it = _unreachable_endpoints.find(ep);
    if (it != _unreachable_endpoints.end()) {
        auto& downtime = it->second;
        return std::chrono::duration_cast<std::chrono::microseconds>(now() - downtime).count();
    } else {
        return 0L;
    }
}

// Depends on
// - on_dead callbacks
// It is called from failure_detector
//
// Runs inside seastar::async context
void gossiper::convict(inet_address endpoint, double phi) {
    auto* state = get_endpoint_state_for_endpoint_ptr(endpoint);
    if (!state || !state->is_alive()) {
        return;
    }

    if (logger.is_enabled(log_level::debug)) {
        logger.debug("Convicting ep={} with status={}", endpoint, get_gossip_status(*state));
        logger.trace("    phi={}, is_dead_state={}", phi, is_dead_state(*state));
    }
    if (is_shutdown(endpoint)) {
        mark_as_shutdown(endpoint);
    } else {
        mark_dead(endpoint, *state);
    }
}

std::set<inet_address> gossiper::get_unreachable_members() {
    std::set<inet_address> ret;
    for (auto&& x : _unreachable_endpoints) {
        ret.insert(x.first);
    }
    return ret;
}

int gossiper::get_max_endpoint_state_version(endpoint_state state) const noexcept {
    int max_version = state.get_heart_beat_state().get_heart_beat_version();
    for (auto& entry : state.get_application_state_map()) {
        auto& value = entry.second;
        max_version = std::max(max_version, value.version);
    }
    return max_version;
}

// Runs inside seastar::async context
void gossiper::evict_from_membership(inet_address endpoint) {
    auto permit = lock_endpoint(endpoint).get0();
    _unreachable_endpoints.erase(endpoint);
    container().invoke_on_all([endpoint] (auto& g) {
        g.endpoint_state_map.erase(endpoint);
    }).get();
    _expire_time_endpoint_map.erase(endpoint);
    fd().remove(endpoint);
    quarantine_endpoint(endpoint);
    logger.debug("evicting {} from gossip", endpoint);
}

void gossiper::quarantine_endpoint(inet_address endpoint) {
    quarantine_endpoint(endpoint, now());
}

void gossiper::quarantine_endpoint(inet_address endpoint, clk::time_point quarantine_start) {
    _just_removed_endpoints[endpoint] = quarantine_start;
}

void gossiper::make_random_gossip_digest(utils::chunked_vector<gossip_digest>& g_digests) {
    int generation = 0;
    int max_version = 0;

    // local epstate will be part of endpoint_state_map
    utils::chunked_vector<inet_address> endpoints;
    for (auto&& x : endpoint_state_map) {
        endpoints.push_back(x.first);
    }
    std::shuffle(endpoints.begin(), endpoints.end(), _random_engine);
    for (auto& endpoint : endpoints) {
        auto es = get_endpoint_state_for_endpoint_ptr(endpoint);
        if (es) {
            auto& eps = *es;
            generation = eps.get_heart_beat_state().get_generation();
            max_version = get_max_endpoint_state_version(eps);
        }
        g_digests.push_back(gossip_digest(endpoint, generation, max_version));
    }
#if 0
    if (logger.isTraceEnabled()) {
        StringBuilder sb = new StringBuilder();
        for (GossipDigest g_digest : g_digests)
        {
            sb.append(g_digest);
            sb.append(" ");
        }
        logger.trace("Gossip Digests are : {}", sb);
    }
#endif
}

future<> gossiper::replicate(inet_address ep, const endpoint_state& es) {
    return container().invoke_on_all([ep, es, orig = this_shard_id(), self = shared_from_this()] (gossiper& g) {
        if (this_shard_id() != orig) {
            g.endpoint_state_map[ep].add_application_state(es);
        }
    });
}

future<> gossiper::replicate(inet_address ep, const std::map<application_state, versioned_value>& src, const utils::chunked_vector<application_state>& changed) {
    return container().invoke_on_all([ep, &src, &changed, orig = this_shard_id(), self = shared_from_this()] (gossiper& g) {
        if (this_shard_id() != orig) {
            for (auto&& key : changed) {
                g.endpoint_state_map[ep].add_application_state(key, src.at(key));
            }
        }
    });
}

future<> gossiper::replicate(inet_address ep, application_state key, const versioned_value& value) {
    return container().invoke_on_all([ep, key, &value, orig = this_shard_id(), self = shared_from_this()] (gossiper& g) {
        if (this_shard_id() != orig) {
            g.endpoint_state_map[ep].add_application_state(key, value);
        }
    });
}

future<> gossiper::advertise_removing(inet_address endpoint, utils::UUID host_id, utils::UUID local_host_id) {
    return seastar::async([this, g = this->shared_from_this(), endpoint, host_id, local_host_id] {
        auto& state = get_endpoint_state(endpoint);
        // remember this node's generation
        int generation = state.get_heart_beat_state().get_generation();
        logger.info("Removing host: {}", host_id);
        auto ring_delay = std::chrono::milliseconds(_cfg.ring_delay_ms());
        logger.info("Sleeping for {}ms to ensure {} does not change", ring_delay.count(), endpoint);
        sleep_abortable(ring_delay, _abort_source).get();
        // make sure it did not change
        auto& eps = get_endpoint_state(endpoint);
        if (eps.get_heart_beat_state().get_generation() != generation) {
            throw std::runtime_error(format("Endpoint {} generation changed while trying to remove it", endpoint));
        }

        // update the other node's generation to mimic it as if it had changed it itself
        logger.info("Advertising removal for {}", endpoint);
        eps.update_timestamp(); // make sure we don't evict it too soon
        eps.get_heart_beat_state().force_newer_generation_unsafe();
        eps.add_application_state(application_state::STATUS, versioned_value::removing_nonlocal(host_id));
        eps.add_application_state(application_state::REMOVAL_COORDINATOR, versioned_value::removal_coordinator(local_host_id));
        endpoint_state_map[endpoint] = eps;
        replicate(endpoint, eps).get();
    });
}

future<> gossiper::advertise_token_removed(inet_address endpoint, utils::UUID host_id) {
    return seastar::async([this, g = this->shared_from_this(), endpoint, host_id] {
        auto& eps = get_endpoint_state(endpoint);
        eps.update_timestamp(); // make sure we don't evict it too soon
        eps.get_heart_beat_state().force_newer_generation_unsafe();
        auto expire_time = compute_expire_time();
        eps.add_application_state(application_state::STATUS, versioned_value::removed_nonlocal(host_id, expire_time.time_since_epoch().count()));
        logger.info("Completing removal of {}", endpoint);
        add_expire_time_for_endpoint(endpoint, expire_time);
        endpoint_state_map[endpoint] = eps;
        replicate(endpoint, eps).get();
        // ensure at least one gossip round occurs before returning
        sleep_abortable(INTERVAL * 2, _abort_source).get();
    });
}

future<> gossiper::unsafe_assassinate_endpoint(sstring address) {
    logger.warn("Gossiper.unsafeAssassinateEndpoint is deprecated and will be removed in the next release; use assassinate_endpoint instead");
    return assassinate_endpoint(address);
}

future<> gossiper::assassinate_endpoint(sstring address) {
    return get_gossiper().invoke_on(0, [address] (auto&& gossiper) {
        return seastar::async([&gossiper, g = gossiper.shared_from_this(), address] {
            inet_address endpoint(address);
            auto permit = gossiper.lock_endpoint(endpoint).get0();
            auto es = gossiper.get_endpoint_state_for_endpoint_ptr(endpoint);
            auto now = gossiper.now();
            int gen = std::chrono::duration_cast<std::chrono::seconds>((now + std::chrono::seconds(60)).time_since_epoch()).count();
            int ver = 9999;
            endpoint_state ep_state = es ? *es : endpoint_state(heart_beat_state(gen, ver));
            std::vector<dht::token> tokens;
            logger.warn("Assassinating {} via gossip", endpoint);
            if (es) {
                tokens = gossiper.get_token_metadata_ptr()->get_tokens(endpoint);
                if (tokens.empty()) {
                    logger.warn("Unable to calculate tokens for {}.  Will use a random one", address);
                    throw std::runtime_error(format("Unable to calculate tokens for {}", endpoint));
                }

                int generation = ep_state.get_heart_beat_state().get_generation();
                int heartbeat = ep_state.get_heart_beat_state().get_heart_beat_version();
                auto ring_delay = std::chrono::milliseconds(gossiper._cfg.ring_delay_ms());
                logger.info("Sleeping for {} ms to ensure {} does not change", ring_delay.count(), endpoint);
                // make sure it did not change
                sleep_abortable(ring_delay, gossiper._abort_source).get();

                es = gossiper.get_endpoint_state_for_endpoint_ptr(endpoint);
                if (!es) {
                    logger.warn("Endpoint {} disappeared while trying to assassinate, continuing anyway", endpoint);
                } else {
                    auto& new_state = *es;
                    if (new_state.get_heart_beat_state().get_generation() != generation) {
                        throw std::runtime_error(format("Endpoint still alive: {} generation changed while trying to assassinate it", endpoint));
                    } else if (new_state.get_heart_beat_state().get_heart_beat_version() != heartbeat) {
                        throw std::runtime_error(format("Endpoint still alive: {} heartbeat changed while trying to assassinate it", endpoint));
                    }
                }
                ep_state.update_timestamp(); // make sure we don't evict it too soon
                ep_state.get_heart_beat_state().force_newer_generation_unsafe();
            }

            // do not pass go, do not collect 200 dollars, just gtfo
            std::unordered_set<dht::token> tokens_set(tokens.begin(), tokens.end());
            auto expire_time = gossiper.compute_expire_time();
            ep_state.add_application_state(application_state::STATUS, versioned_value::left(tokens_set, expire_time.time_since_epoch().count()));
            gossiper.handle_major_state_change(endpoint, ep_state);
            sleep_abortable(INTERVAL * 4, gossiper._abort_source).get();
            logger.warn("Finished assassinating {}", endpoint);
        });
    });
}

bool gossiper::is_known_endpoint(inet_address endpoint) const noexcept {
    return endpoint_state_map.contains(endpoint);
}

future<int> gossiper::get_current_generation_number(inet_address endpoint) {
    return get_gossiper().invoke_on(0, [endpoint] (auto&& gossiper) {
        return gossiper.get_endpoint_state(endpoint).get_heart_beat_state().get_generation();
    });
}

future<int> gossiper::get_current_heart_beat_version(inet_address endpoint) {
    return get_gossiper().invoke_on(0, [endpoint] (auto&& gossiper) {
        return gossiper.get_endpoint_state(endpoint).get_heart_beat_state().get_heart_beat_version();
    });
}

future<> gossiper::do_gossip_to_live_member(gossip_digest_syn message, gms::inet_address ep) {
    return send_gossip(message, {ep});
}

future<> gossiper::do_gossip_to_unreachable_member(gossip_digest_syn message) {
    double live_endpoint_count = _live_endpoints.size();
    double unreachable_endpoint_count = _unreachable_endpoints.size();
    if (unreachable_endpoint_count > 0) {
        /* based on some probability */
        double prob = unreachable_endpoint_count / (live_endpoint_count + 1);
        std::uniform_real_distribution<double> dist(0, 1);
        double rand_dbl = dist(_random_engine);
        if (rand_dbl < prob) {
            std::set<inet_address> addrs;
            for (auto&& x : _unreachable_endpoints) {
                // Ignore the node which is decommissioned
                if (get_gossip_status(x.first) != sstring(versioned_value::STATUS_LEFT)) {
                    addrs.insert(x.first);
                }
            }
            logger.trace("do_gossip_to_unreachable_member: live_endpoint nr={} unreachable_endpoints nr={}",
                live_endpoint_count, unreachable_endpoint_count);
            return send_gossip(message, addrs);
        }
    }
    return make_ready_future<>();
}

bool gossiper::is_gossip_only_member(inet_address endpoint) {
    auto es = get_endpoint_state_for_endpoint_ptr(endpoint);
    if (!es) {
        return false;
    }
    return !is_dead_state(*es) && !get_token_metadata_ptr()->is_member(endpoint);
}

clk::time_point gossiper::get_expire_time_for_endpoint(inet_address endpoint) const noexcept {
    /* default expire_time is A_VERY_LONG_TIME */
    auto it = _expire_time_endpoint_map.find(endpoint);
    if (it == _expire_time_endpoint_map.end()) {
        return compute_expire_time();
    } else {
        auto stored_time = it->second;
        return stored_time;
    }
}

const endpoint_state* gossiper::get_endpoint_state_for_endpoint_ptr(inet_address ep) const noexcept {
    auto it = endpoint_state_map.find(ep);
    if (it == endpoint_state_map.end()) {
        return nullptr;
    } else {
        return &it->second;
    }
}

endpoint_state* gossiper::get_endpoint_state_for_endpoint_ptr(inet_address ep) noexcept {
    auto it = endpoint_state_map.find(ep);
    if (it == endpoint_state_map.end()) {
        return nullptr;
    } else {
        return &it->second;
    }
}

endpoint_state& gossiper::get_endpoint_state(inet_address ep) {
    auto ptr = get_endpoint_state_for_endpoint_ptr(ep);
    if (!ptr) {
        throw std::out_of_range(format("ep={}", ep));
    }
    return *ptr;
}

std::optional<endpoint_state> gossiper::get_endpoint_state_for_endpoint(inet_address ep) const noexcept {
    auto it = endpoint_state_map.find(ep);
    if (it == endpoint_state_map.end()) {
        return {};
    } else {
        return it->second;
    }
}

future<> gossiper::reset_endpoint_state_map() {
    _unreachable_endpoints.clear();
    _live_endpoints.clear();
    return container().invoke_on_all([] (gossiper& g) {
        g.endpoint_state_map.clear();
    });
}

const std::unordered_map<inet_address, endpoint_state>& gms::gossiper::get_endpoint_states() const noexcept {
    return endpoint_state_map;
}

bool gossiper::uses_host_id(inet_address endpoint) const {
    return _messaging.knows_version(endpoint) ||
            get_application_state_ptr(endpoint, application_state::NET_VERSION);
}

bool gossiper::is_cql_ready(const inet_address& endpoint) const {
    // Note:
    // - New scylla node always send application_state::RPC_READY = false when
    // the node boots and send application_state::RPC_READY = true when cql
    // server is up
    // - Old scylla node that does not support the application_state::RPC_READY
    // never has application_state::RPC_READY in the endpoint_state, we can
    // only think their cql server is up, so we return true here if
    // application_state::RPC_READY is not present
    auto* eps = get_endpoint_state_for_endpoint_ptr(endpoint);
    if (!eps) {
        logger.debug("Node {} does not have RPC_READY application_state, return is_cql_ready=true", endpoint);
        return true;
    }
    auto ready = eps->is_cql_ready();
    logger.debug("Node {}: is_cql_ready={}",  endpoint, ready);
    return ready;
}

utils::UUID gossiper::get_host_id(inet_address endpoint) const {
    if (!uses_host_id(endpoint)) {
        throw std::runtime_error(format("Host {} does not use new-style tokens!", endpoint));
    }
    auto app_state = get_application_state_ptr(endpoint, application_state::HOST_ID);
    if (!app_state) {
        throw std::runtime_error(format("Host {} does not have HOST_ID application_state", endpoint));
    }
    return utils::UUID(app_state->value);
}

std::optional<endpoint_state> gossiper::get_state_for_version_bigger_than(inet_address for_endpoint, int version) {
    std::optional<endpoint_state> reqd_endpoint_state;
    auto es = get_endpoint_state_for_endpoint_ptr(for_endpoint);
    if (es) {
        auto& eps = *es;
        /*
             * Here we try to include the Heart Beat state only if it is
             * greater than the version passed in. It might happen that
             * the heart beat version maybe lesser than the version passed
             * in and some application state has a version that is greater
             * than the version passed in. In this case we also send the old
             * heart beat and throw it away on the receiver if it is redundant.
            */
        int local_hb_version = eps.get_heart_beat_state().get_heart_beat_version();
        if (local_hb_version > version) {
            reqd_endpoint_state.emplace(eps.get_heart_beat_state());
            logger.trace("local heartbeat version {} greater than {} for {}", local_hb_version, version, for_endpoint);
        }
        /* Accumulate all application states whose versions are greater than "version" variable */
        for (auto& entry : eps.get_application_state_map()) {
            auto& value = entry.second;
            if (value.version > version) {
                if (!reqd_endpoint_state) {
                    reqd_endpoint_state.emplace(eps.get_heart_beat_state());
                }
                auto& key = entry.first;
                logger.trace("Adding state of {}, {}: {}" , for_endpoint, key, value.value);
                reqd_endpoint_state->add_application_state(key, value);
            }
        }
    }
    return reqd_endpoint_state;
}

int gossiper::compare_endpoint_startup(inet_address addr1, inet_address addr2) {
    auto* ep1 = get_endpoint_state_for_endpoint_ptr(addr1);
    auto* ep2 = get_endpoint_state_for_endpoint_ptr(addr2);
    if (!ep1 || !ep2) {
        auto err = format("Can not get endpoint_state for {} or {}", addr1, addr2);
        logger.warn("{}", err);
        throw std::runtime_error(err);
    }
    return ep1->get_heart_beat_state().get_generation() - ep2->get_heart_beat_state().get_generation();
}

void gossiper::notify_failure_detector(const std::map<inet_address, endpoint_state>& remoteEpStateMap) {
    for (auto& entry : remoteEpStateMap) {
        notify_failure_detector(entry.first, entry.second);
    }
}

// Runs inside seastar::async context
void gossiper::mark_alive(inet_address addr, endpoint_state& local_state) {
    // if (MessagingService.instance().getVersion(addr) < MessagingService.VERSION_20) {
    //     real_mark_alive(addr, local_state);
    //     return;
    // }
    auto inserted = _pending_mark_alive_endpoints.insert(addr).second;
    if (inserted) {
        // The node is not in the _pending_mark_alive_endpoints
        logger.debug("Mark Node {} alive with EchoMessage", addr);
    } else {
        // We are in the progress of marking this node alive
        logger.debug("Node {} is being marked as up, ignoring duplicated mark alive operation", addr);
        return;
    }

    local_state.mark_dead();
    msg_addr id = get_msg_addr(addr);
    logger.trace("Sending a EchoMessage to {}", id);
    // Do it in the background.
    (void)_messaging.send_gossip_echo(id).then([this, addr] {
        logger.trace("Got EchoMessage Reply");
        return seastar::async([this, addr] {
            // After sending echo message, the Node might not be in the
            // endpoint_state_map anymore, use the reference of local_state
            // might cause user-after-free
            auto es = get_endpoint_state_for_endpoint_ptr(addr);
            if (!es) {
                logger.info("Node {} is not in endpoint_state_map anymore", addr);
            } else {
                endpoint_state& state = *es;
                logger.debug("Mark Node {} alive after EchoMessage", addr);
                real_mark_alive(addr, state);
            }
        });
    }).finally([this, addr] {
        _pending_mark_alive_endpoints.erase(addr);
    }).handle_exception([addr] (auto ep) {
        logger.warn("Fail to send EchoMessage to {}: {}", addr, ep);
    });
}

// Runs inside seastar::async context
void gossiper::real_mark_alive(inet_address addr, endpoint_state& local_state) {
    logger.trace("marking as alive {}", addr);

    // Do not mark a node with status shutdown as UP.
    auto status = get_gossip_status(local_state);
    if (status == sstring(versioned_value::SHUTDOWN)) {
        logger.warn("Skip marking node {} with status = {} as UP", addr, status);
        return;
    }

    local_state.mark_alive();
    local_state.update_timestamp(); // prevents do_status_check from racing us and evicting if it was down > A_VERY_LONG_TIME

    logger.debug("removing expire time for endpoint : {}", addr);
    _unreachable_endpoints.erase(addr);
    _expire_time_endpoint_map.erase(addr);

    auto it_ = std::find(_live_endpoints.begin(), _live_endpoints.end(), addr);
    bool was_live = it_ != _live_endpoints.end();
    if (was_live) {
        return;
    }

    _live_endpoints.push_back(addr);
    if (_endpoints_to_talk_with.empty()) {
        _endpoints_to_talk_with.push_back({addr});
    } else {
        _endpoints_to_talk_with.front().push_back(addr);
    }

    if (!_in_shadow_round) {
        logger.info("InetAddress {} is now UP, status = {}", addr, status);
    }

    _subscribers.for_each([addr, local_state] (shared_ptr<i_endpoint_state_change_subscriber> subscriber) {
        subscriber->on_alive(addr, local_state);
        logger.trace("Notified {}", fmt::ptr(subscriber.get()));
    });
}

// Runs inside seastar::async context
void gossiper::mark_dead(inet_address addr, endpoint_state& local_state) {
    logger.trace("marking as down {}", addr);
    local_state.mark_dead();
    _live_endpoints.resize(std::distance(_live_endpoints.begin(), std::remove(_live_endpoints.begin(), _live_endpoints.end(), addr)));
    _unreachable_endpoints[addr] = now();
    logger.info("InetAddress {} is now DOWN, status = {}", addr, get_gossip_status(local_state));
    _subscribers.for_each([addr, local_state] (shared_ptr<i_endpoint_state_change_subscriber> subscriber) {
        subscriber->on_dead(addr, local_state);
        logger.trace("Notified {}", fmt::ptr(subscriber.get()));
    });
}

// Runs inside seastar::async context
void gossiper::handle_major_state_change(inet_address ep, const endpoint_state& eps) {
    auto eps_old = get_endpoint_state_for_endpoint(ep);
    if (!is_dead_state(eps) && !_in_shadow_round) {
        if (endpoint_state_map.contains(ep))  {
            logger.debug("Node {} has restarted, now UP, status = {}", ep, get_gossip_status(eps));
        } else {
            logger.debug("Node {} is now part of the cluster, status = {}", ep, get_gossip_status(eps));
        }
    }
    logger.trace("Adding endpoint state for {}, status = {}", ep, get_gossip_status(eps));
    endpoint_state_map[ep] = eps;
    replicate(ep, eps).get();

    if (_in_shadow_round) {
        // In shadow round, we only interested in the peer's endpoint_state,
        // e.g., gossip features, host_id, tokens. No need to call the
        // on_restart or on_join callbacks or to go through the mark alive
        // procedure with EchoMessage gossip message. We will do them during
        // normal gossip runs anyway.
        logger.debug("In shadow round addr={}, eps={}", ep, eps);
        return;
    }

    if (eps_old) {
        // the node restarted: it is up to the subscriber to take whatever action is necessary
        _subscribers.for_each([ep, eps_old] (shared_ptr<i_endpoint_state_change_subscriber> subscriber) {
            subscriber->on_restart(ep, *eps_old);
        });
    }

    auto& ep_state = endpoint_state_map.at(ep);
    if (!is_dead_state(ep_state)) {
        mark_alive(ep, ep_state);
    } else {
        logger.debug("Not marking {} alive due to dead state {}", ep, get_gossip_status(eps));
        mark_dead(ep, ep_state);
    }

    auto* eps_new = get_endpoint_state_for_endpoint_ptr(ep);
    if (eps_new) {
        _subscribers.for_each([ep, eps_new] (shared_ptr<i_endpoint_state_change_subscriber> subscriber) {
            subscriber->on_join(ep, *eps_new);
        });
    }
    // check this at the end so nodes will learn about the endpoint
    if (is_shutdown(ep)) {
        mark_as_shutdown(ep);
    }
}

bool gossiper::is_dead_state(const endpoint_state& eps) const {
    auto state = get_gossip_status(eps);
    for (auto& deadstate : DEAD_STATES) {
        if (state == deadstate) {
            return true;
        }
    }
    return false;
}

bool gossiper::is_shutdown(const inet_address& endpoint) const {
    return get_gossip_status(endpoint) == sstring(versioned_value::SHUTDOWN);
}

bool gossiper::is_normal(const inet_address& endpoint) const {
    return get_gossip_status(endpoint) == sstring(versioned_value::STATUS_NORMAL);
}

bool gossiper::is_silent_shutdown_state(const endpoint_state& ep_state) const{
    auto state = get_gossip_status(ep_state);
    for (auto& deadstate : SILENT_SHUTDOWN_STATES) {
        if (state == deadstate) {
            return true;
        }
    }
    return false;
}

// Runs inside seastar::async context
void gossiper::apply_new_states(inet_address addr, endpoint_state& local_state, const endpoint_state& remote_state) {
    // don't assert here, since if the node restarts the version will go back to zero
    //int oldVersion = local_state.get_heart_beat_state().get_heart_beat_version();

    local_state.set_heart_beat_state_and_update_timestamp(remote_state.get_heart_beat_state());
    // if (logger.isTraceEnabled()) {
    //     logger.trace("Updating heartbeat state version to {} from {} for {} ...",
    //     local_state.get_heart_beat_state().get_heart_beat_version(), oldVersion, addr);
    // }

    utils::chunked_vector<application_state> changed;
    auto&& remote_map = remote_state.get_application_state_map();

    // Exceptions thrown from listeners will result in abort because that could leave the node in a bad
    // state indefinitely. Unless the value changes again, we wouldn't retry notifications.
    // Some values are set only once, so listeners would never be re-run.
    // Listeners should decide which failures are non-fatal and swallow them.
    auto run_listeners = seastar::defer([&] () noexcept {
        for (auto&& key : changed) {
            do_on_change_notifications(addr, key, remote_map.at(key));
        }
    });

    // We must replicate endpoint states before listeners run.
    // Exceptions during replication will cause abort because node's state
    // would be inconsistent across shards. Changes listeners depend on state
    // being replicated to all shards.
    auto replicate_changes = seastar::defer([&] () noexcept {
        replicate(addr, remote_map, changed).get();
    });

    // we need to make two loops here, one to apply, then another to notify,
    // this way all states in an update are present and current when the notifications are received
    for (const auto& remote_entry : remote_map) {
        const auto& remote_key = remote_entry.first;
        const auto& remote_value = remote_entry.second;
        auto remote_gen = remote_state.get_heart_beat_state().get_generation();
        auto local_gen = local_state.get_heart_beat_state().get_generation();
        if(remote_gen != local_gen) {
            auto err = format("Remote generation {:d} != local generation {:d}", remote_gen, local_gen);
            logger.warn("{}", err);
            throw std::runtime_error(err);
        }

        const versioned_value* local_val = local_state.get_application_state_ptr(remote_key);
        if (!local_val || remote_value.version > local_val->version) {
            changed.push_back(remote_key);
            local_state.add_application_state(remote_key, remote_value);
        }
    }
}

// Runs inside seastar::async context
void gossiper::do_before_change_notifications(inet_address addr, const endpoint_state& ep_state, const application_state& ap_state, const versioned_value& new_value) {
    _subscribers.for_each([addr, ep_state, ap_state, new_value] (shared_ptr<i_endpoint_state_change_subscriber> subscriber) {
        subscriber->before_change(addr, ep_state, ap_state, new_value);
    });
}

// Runs inside seastar::async context
void gossiper::do_on_change_notifications(inet_address addr, const application_state& state, const versioned_value& value) {
    _subscribers.for_each([addr, state, value] (shared_ptr<i_endpoint_state_change_subscriber> subscriber) {
        subscriber->on_change(addr, state, value);
    });
}

void gossiper::request_all(gossip_digest& g_digest,
    utils::chunked_vector<gossip_digest>& delta_gossip_digest_list, int remote_generation) {
    /* We are here since we have no data for this endpoint locally so request everthing. */
    delta_gossip_digest_list.emplace_back(g_digest.get_endpoint(), remote_generation, 0);
    logger.trace("request_all for {}", g_digest.get_endpoint());
}

void gossiper::send_all(gossip_digest& g_digest,
    std::map<inet_address, endpoint_state>& delta_ep_state_map,
    int max_remote_version) {
    auto ep = g_digest.get_endpoint();
    logger.trace("send_all(): ep={}, version > {}", ep, max_remote_version);
    auto local_ep_state_ptr = get_state_for_version_bigger_than(ep, max_remote_version);
    if (local_ep_state_ptr) {
        delta_ep_state_map[ep] = *local_ep_state_ptr;
    }
}

void gossiper::examine_gossiper(utils::chunked_vector<gossip_digest>& g_digest_list,
    utils::chunked_vector<gossip_digest>& delta_gossip_digest_list,
    std::map<inet_address, endpoint_state>& delta_ep_state_map) {
    if (g_digest_list.size() == 0) {
        /* we've been sent a *completely* empty syn, which should normally
             * never happen since an endpoint will at least send a syn with
             * itself.  If this is happening then the node is attempting shadow
             * gossip, and we should reply with everything we know.
             */
        logger.debug("Shadow request received, adding all states");
        for (auto& entry : endpoint_state_map) {
            g_digest_list.emplace_back(entry.first, 0, 0);
        }
    }
    for (gossip_digest& g_digest : g_digest_list) {
        int remote_generation = g_digest.get_generation();
        int max_remote_version = g_digest.get_max_version();
        /* Get state associated with the end point in digest */
        auto&& ep = g_digest.get_endpoint();
        auto es = get_endpoint_state_for_endpoint_ptr(ep);
        /* Here we need to fire a GossipDigestAckMessage. If we have some
             * data associated with this endpoint locally then we follow the
             * "if" path of the logic. If we have absolutely nothing for this
             * endpoint we need to request all the data for this endpoint.
             */
        if (es) {
            endpoint_state& ep_state_ptr = *es;
            int local_generation = ep_state_ptr.get_heart_beat_state().get_generation();
            /* get the max version of all keys in the state associated with this endpoint */
            int max_local_version = get_max_endpoint_state_version(ep_state_ptr);
            logger.trace("examine_gossiper(): ep={}, remote={}.{}, local={}.{}", ep,
                remote_generation, max_remote_version, local_generation, max_local_version);
            if (remote_generation == local_generation && max_remote_version == max_local_version) {
                continue;
            }

            if (remote_generation > local_generation) {
                /* we request everything from the gossiper */
                request_all(g_digest, delta_gossip_digest_list, remote_generation);
            } else if (remote_generation < local_generation) {
                /* send all data with generation = localgeneration and version > 0 */
                send_all(g_digest, delta_ep_state_map, 0);
            } else if (remote_generation == local_generation) {
                /*
                 * If the max remote version is greater then we request the
                 * remote endpoint send us all the data for this endpoint
                 * with version greater than the max version number we have
                 * locally for this endpoint.
                 *
                 * If the max remote version is lesser, then we send all
                 * the data we have locally for this endpoint with version
                 * greater than the max remote version.
                 */
                if (max_remote_version > max_local_version) {
                    logger.trace("examine_gossiper(): requesting version > {} from {}", max_local_version, g_digest.get_endpoint());
                    delta_gossip_digest_list.emplace_back(g_digest.get_endpoint(), remote_generation, max_local_version);
                } else if (max_remote_version < max_local_version) {
                    /* send all data with generation = localgeneration and version > max_remote_version */
                    send_all(g_digest, delta_ep_state_map, max_remote_version);
                }
            }
        } else {
            /* We are here since we have no data for this endpoint locally so request everything. */
            request_all(g_digest, delta_gossip_digest_list, remote_generation);
        }
    }
}

future<> gossiper::start_gossiping(int generation_number, bind_messaging_port do_bind) {
    return start_gossiping(generation_number, std::map<application_state, versioned_value>(), do_bind);
}

future<> gossiper::start_gossiping(int generation_nbr, std::map<application_state, versioned_value> preload_local_states, bind_messaging_port do_bind) {
    // Although gossiper runs on cpu0 only, we need to listen incoming gossip
    // message on all cpus and forard them to cpu0 to process.
    return get_gossiper().invoke_on_all([do_bind] (gossiper& g) {
        return g.init_messaging_service_handler(do_bind);
    }).then([this, generation_nbr, preload_local_states] () mutable {
        build_seeds_list();
        if (_cfg.force_gossip_generation() > 0) {
            generation_nbr = _cfg.force_gossip_generation();
            logger.warn("Use the generation number provided by user: generation = {}", generation_nbr);
        }
        endpoint_state& local_state = endpoint_state_map[get_broadcast_address()];
        local_state.set_heart_beat_state_and_update_timestamp(heart_beat_state(generation_nbr));
        local_state.mark_alive();
        for (auto& entry : preload_local_states) {
            local_state.add_application_state(entry.first, entry.second);
        }

        auto generation = local_state.get_heart_beat_state().get_generation();

        return replicate(get_broadcast_address(), local_state).then([] {
            //notify snitches that Gossiper is about to start
            return locator::i_endpoint_snitch::get_local_snitch_ptr()->gossiper_starting();
        }).then([this, generation] {
            logger.trace("gossip started with generation {}", generation);
            _enabled = true;
            _nr_run = 0;
            _scheduled_gossip_task.arm(INTERVAL);
            return make_ready_future<>();
        });
    });
}

future<> gossiper::do_shadow_round(std::unordered_set<gms::inet_address> nodes, bind_messaging_port do_bind) {
    return seastar::async([this, g = this->shared_from_this(), nodes = std::move(nodes), do_bind] () mutable {
        get_gossiper().invoke_on_all([do_bind] (gossiper& g) {
            return g.init_messaging_service_handler(do_bind);
        }).get();
        nodes.erase(get_broadcast_address());
        gossip_get_endpoint_states_request request{{
            gms::application_state::STATUS,
            gms::application_state::HOST_ID,
            gms::application_state::TOKENS,
            gms::application_state::SUPPORTED_FEATURES,
            gms::application_state::SNITCH_NAME}};
        logger.info("Gossip shadow round started with nodes={}", nodes);
        std::unordered_set<gms::inet_address> nodes_talked;
        size_t nodes_down = 0;
        auto start_time = clk::now();
        bool fall_back_to_syn_msg = false;
        std::list<gms::gossip_get_endpoint_states_response> responses;
        for (;;) {
            parallel_for_each(nodes.begin(), nodes.end(), [this, &request, &responses, &nodes_talked, &nodes_down, &fall_back_to_syn_msg] (gms::inet_address node) {
                logger.debug("Sent get_endpoint_states request to {}, request={}", node, request.application_states);
                return _messaging.send_gossip_get_endpoint_states(msg_addr(node), std::chrono::milliseconds(5000), request).then(
                        [node, &nodes_talked, &responses] (gms::gossip_get_endpoint_states_response response) {
                    logger.debug("Got get_endpoint_states response from {}, response={}", node, response.endpoint_state_map);
                    responses.push_back(std::move(response));
                    nodes_talked.insert(node);
                }).handle_exception_type([node, &fall_back_to_syn_msg] (seastar::rpc::unknown_verb_error&) {
                    logger.warn("Node {} does not support get_endpoint_states verb", node);
                    fall_back_to_syn_msg = true;
                }).handle_exception_type([node, &nodes_down] (seastar::rpc::timeout_error&) {
                    logger.warn("The get_endpoint_states verb to node {} was timeout", node);
                }).handle_exception_type([node, &nodes_down] (seastar::rpc::closed_error&) {
                    nodes_down++;
                    logger.warn("Node {} is down for get_endpoint_states verb", node);
                });
            }).get();
            for (auto& response : responses) {
                apply_state_locally_without_listener_notification(response.endpoint_state_map);
            }
            if (!nodes_talked.empty()) {
                break;
            }
            if (nodes_down == nodes.size()) {
                logger.warn("All nodes={} are down for get_endpoint_states verb. Skip ShadowRound.", nodes);
                break;
            }
            if (fall_back_to_syn_msg) {
                break;
            }
            if (clk::now() > start_time + std::chrono::milliseconds(_cfg.shadow_round_ms())) {
                throw std::runtime_error(format("Unable to gossip with any nodes={} (ShadowRound).", nodes));
            }
            sleep_abortable(std::chrono::seconds(1), _abort_source).get();
            logger.info("Connect nodes={} again ... ({} seconds passed)",
                    nodes, std::chrono::duration_cast<std::chrono::seconds>(clk::now() - start_time).count());
        }
        if (fall_back_to_syn_msg) {
            logger.info("Fallback to old method for ShadowRound");
            auto t = clk::now();
            _in_shadow_round = true;
            while (this->_in_shadow_round) {
                // send a completely empty syn
                for (const auto& node : nodes) {
                    utils::chunked_vector<gossip_digest> digests;
                    gossip_digest_syn message(get_cluster_name(), get_partitioner_name(), digests);
                    auto id = get_msg_addr(node);
                    logger.trace("Sending a GossipDigestSyn (ShadowRound) to {} ...", id);
                    // Do it in the background.
                    (void)_messaging.send_gossip_digest_syn(id, std::move(message)).handle_exception([id] (auto ep) {
                        logger.trace("Fail to send GossipDigestSyn (ShadowRound) to {}: {}", id, ep);
                    });
                }
                sleep_abortable(std::chrono::seconds(1), _abort_source).get();
                if (this->_in_shadow_round) {
                    if (clk::now() > t + std::chrono::milliseconds(_cfg.shadow_round_ms())) {
                        throw std::runtime_error(format("Unable to gossip with any nodes={} (ShadowRound),", nodes));
                    }
                    logger.info("Connect nodes={} again ... ({} seconds passed)",
                            nodes, std::chrono::duration_cast<std::chrono::seconds>(clk::now() - t).count());
                }
            }
        }
        logger.info("Gossip shadow round finisehd with nodes_talked={}", nodes_talked);
    });
}

void gossiper::build_seeds_list() {
    for (inet_address seed : get_seeds() ) {
        if (seed == get_broadcast_address()) {
            continue;
        }
        _seeds.emplace(seed);
    }
}

void gossiper::maybe_initialize_local_state(int generation_nbr) {
    heart_beat_state hb_state(generation_nbr);
    endpoint_state local_state(hb_state);
    local_state.mark_alive();
    inet_address ep = get_broadcast_address();
    if (!endpoint_state_map.contains(ep)) {
        endpoint_state_map.emplace(ep, local_state);
    }
}

// Runs inside seastar::async context
void gossiper::add_saved_endpoint(inet_address ep) {
    if (ep == get_broadcast_address()) {
        logger.debug("Attempt to add self as saved endpoint");
        return;
    }

    //preserve any previously known, in-memory data about the endpoint (such as DC, RACK, and so on)
    auto ep_state = endpoint_state(heart_beat_state(0));
    auto es = get_endpoint_state_for_endpoint_ptr(ep);
    if (es) {
        ep_state = *es;
        logger.debug("not replacing a previous ep_state for {}, but reusing it: {}", ep, ep_state);
        ep_state.set_heart_beat_state_and_update_timestamp(heart_beat_state(0));
    }
    const auto tmptr = get_token_metadata_ptr();
    auto tokens = tmptr->get_tokens(ep);
    if (!tokens.empty()) {
        std::unordered_set<dht::token> tokens_set(tokens.begin(), tokens.end());
        ep_state.add_application_state(gms::application_state::TOKENS, versioned_value::tokens(tokens_set));
    }
    auto host_id = tmptr->get_host_id_if_known(ep);
    if (host_id) {
        ep_state.add_application_state(gms::application_state::HOST_ID, versioned_value::host_id(host_id.value()));
    }
    ep_state.mark_dead();
    endpoint_state_map[ep] = ep_state;
    replicate(ep, ep_state).get();
    _unreachable_endpoints[ep] = now();
    logger.trace("Adding saved endpoint {} {}", ep, ep_state.get_heart_beat_state().get_generation());
}

future<> gossiper::add_local_application_state(application_state state, versioned_value value) {
    return add_local_application_state({ {std::move(state), std::move(value)} });
}

future<> gossiper::add_local_application_state(std::initializer_list<std::pair<application_state, utils::in<versioned_value>>> args) {
    using in_pair_type = std::pair<application_state, utils::in<versioned_value>>;
    using out_pair_type = std::pair<application_state, versioned_value>;
    using vector_type = std::list<out_pair_type>;

    return add_local_application_state(boost::copy_range<vector_type>(args | boost::adaptors::transformed([](const in_pair_type& p) {
        return out_pair_type(p.first, p.second.move());
    })));
}


// Depends on:
// - before_change callbacks
// - on_change callbacks
// #2894. Similar to origin fix, but relies on non-interruptability to ensure we apply
// values "in order".
//
// NOTE: having the values being actual versioned values here is sort of pointless, because
// we overwrite the version to ensure the set is monotonic. However, it does not break anything,
// and changing this tends to spread widely (see versioned_value::factory), so that can be its own
// change later, if needed.
// Retaining the slightly broken signature is also cosistent with origin. Hooray.
//
future<> gossiper::add_local_application_state(std::list<std::pair<application_state, versioned_value>> states) {
    if (states.empty()) {
        return make_ready_future<>();
    }
    return container().invoke_on(0, [states = std::move(states)] (gossiper& gossiper) mutable {
        return seastar::async([g = gossiper.shared_from_this(), states = std::move(states)]() mutable {
            auto& gossiper = *g;
            inet_address ep_addr = gossiper.get_broadcast_address();
            // for symmetry with other apply, use endpoint lock for our own address.
            auto permit = gossiper.lock_endpoint(ep_addr).get0();
            auto es = gossiper.get_endpoint_state_for_endpoint_ptr(ep_addr);
            if (!es) {
                auto err = format("endpoint_state_map does not contain endpoint = {}, application_states = {}",
                                  ep_addr, states);
                logger.error("{}", err);
                throw std::runtime_error(err);
            }

            endpoint_state ep_state_before = *es;

            for (auto& p : states) {
                auto& state = p.first;
                auto& value = p.second;
                // Fire "before change" notifications:
                // Not explicit, but apparently we allow this to defer (inside out implicit seastar::async)
                gossiper.do_before_change_notifications(ep_addr, ep_state_before, state, value);
            }

            es = gossiper.get_endpoint_state_for_endpoint_ptr(ep_addr);
            if (!es) {
                return;
            }

            for (auto& p : states) {
                auto& state = p.first;
                auto& value = p.second;
                // Notifications may have taken some time, so preventively raise the version
                // of the new value, otherwise it could be ignored by the remote node
                // if another value with a newer version was received in the meantime:
                value = versioned_value::clone_with_higher_version(value);
                // Add to local application state
                es->add_application_state(state, value);
            }
            for (auto& p : states) {
                auto& state = p.first;
                auto& value = p.second;
                // fire "on change" notifications:
                // now we might defer again, so this could be reordered. But we've
                // ensured the whole set of values are monotonically versioned and
                // applied to endpoint state.
                gossiper.replicate(ep_addr, state, value).get();
                gossiper.do_on_change_notifications(ep_addr, state, value);
            }
        }).handle_exception([] (auto ep) {
            logger.warn("Fail to apply application_state: {}", ep);
        });
    });
}

future<> gossiper::do_stop_gossiping() {
    if (!is_enabled()) {
        logger.info("gossip is already stopped");
        // Verbs might have been registered by do_shadow_round(), but
        // gossiper itself was not enabled after it...
        if (_ms_registered) {
            return get_gossiper().invoke_on_all(&gossiper::uninit_messaging_service_handler);
        }
        return make_ready_future<>();
    }
    return seastar::async([this, g = this->shared_from_this()] {
        auto* my_ep_state = get_endpoint_state_for_endpoint_ptr(get_broadcast_address());
        if (my_ep_state) {
            logger.info("My status = {}", get_gossip_status(*my_ep_state));
        }
        if (my_ep_state && !is_silent_shutdown_state(*my_ep_state)) {
            logger.info("Announcing shutdown");
            add_local_application_state(application_state::STATUS, versioned_value::shutdown(true)).get();
            auto live_endpoints = _live_endpoints;
            for (inet_address addr : live_endpoints) {
                msg_addr id = get_msg_addr(addr);
                logger.trace("Sending a GossipShutdown to {}", id);
                _messaging.send_gossip_shutdown(id, get_broadcast_address()).then_wrapped([id] (auto&&f) {
                    try {
                        f.get();
                        logger.trace("Got GossipShutdown Reply");
                    } catch (...) {
                        logger.warn("Fail to send GossipShutdown to {}: {}", id, std::current_exception());
                    }
                    return make_ready_future<>();
                }).get();
            }
            sleep(std::chrono::milliseconds(_cfg.shutdown_announce_in_ms())).get();
        } else {
            logger.warn("No local state or state is in silent shutdown, not announcing shutdown");
        }
        logger.info("Disable and wait for gossip loop started");
        // Set disable flag and cancel the timer makes sure gossip loop will not be scheduled
        _enabled = false;
        _scheduled_gossip_task.cancel();
        // Take the semaphore makes sure existing gossip loop is finished
        seastar::with_semaphore(_callback_running, 1, [] {
            logger.info("Disable and wait for gossip loop finished");
            return get_gossiper().invoke_on_all([] (gossiper& g) {
                if (this_shard_id() == 0) {
                    g.fd().unregister_failure_detection_event_listener(&g);
                }
                g._features_condvar.broken();
                return g.uninit_messaging_service_handler();
            });
        }).get();
        logger.info("Gossip is now stopped");
    });
}

future<> stop_gossiping() {
    return smp::submit_to(0, [] {
        if (get_gossiper().local_is_initialized()) {
            return get_local_gossiper().do_stop_gossiping();
        }
        return make_ready_future<>();
    });
}

future<> gossiper::stop() {
    return make_ready_future();
}

bool gossiper::is_enabled() const {
    return _enabled;
}

void gossiper::goto_shadow_round() {
    _in_shadow_round = true;
}

void gossiper::finish_shadow_round() {
    _in_shadow_round = false;
}

bool gossiper::is_in_shadow_round() const {
    return _in_shadow_round;
}

void gossiper::add_expire_time_for_endpoint(inet_address endpoint, clk::time_point expire_time) {
    char expire_time_buf[100];
    auto expire_time_tm = clk::to_time_t(expire_time);
    auto now_ = now();
    ::tm t_buf;
    strftime(expire_time_buf, sizeof(expire_time_buf), "%Y-%m-%d %T", ::localtime_r(&expire_time_tm, &t_buf));
    auto diff = std::chrono::duration_cast<std::chrono::seconds>(expire_time - now_).count();
    logger.info("Node {} will be removed from gossip at [{}]: (expire = {}, now = {}, diff = {} seconds)",
            endpoint, expire_time_buf, expire_time.time_since_epoch().count(),
            now_.time_since_epoch().count(), diff);
    _expire_time_endpoint_map[endpoint] = expire_time;
}

clk::time_point gossiper::compute_expire_time() {
    return now() + A_VERY_LONG_TIME;
}

void gossiper::dump_endpoint_state_map() {
    logger.info("=== endpoint_state_map dump starts == ");
    for (auto& x : endpoint_state_map) {
        logger.info("endpoint={}, endpoint_state={}", x.first, x.second);
    }
    logger.info("=== endpoint_state_map dump ends ===");
}

void gossiper::debug_show() {
    auto reporter = std::make_shared<timer<std::chrono::steady_clock>>();
    reporter->set_callback ([reporter] {
        auto& gossiper = gms::get_local_gossiper();
        gossiper.dump_endpoint_state_map();
    });
    reporter->arm_periodic(std::chrono::milliseconds(1000));
}

bool gossiper::is_alive(inet_address ep) const {
    if (ep == get_broadcast_address()) {
        return true;
    }
    auto* eps = get_endpoint_state_for_endpoint_ptr(std::move(ep));
    // we could assert not-null, but having isAlive fail screws a node over so badly that
    // it's worth being defensive here so minor bugs don't cause disproportionate
    // badness.  (See CASSANDRA-1463 for an example).
    if (eps) {
        return eps->is_alive();
    }
    logger.warn("unknown endpoint {}", ep);
    return false;
}

const versioned_value* gossiper::get_application_state_ptr(inet_address endpoint, application_state appstate) const noexcept {
    auto* eps = get_endpoint_state_for_endpoint_ptr(std::move(endpoint));
    if (!eps) {
        return nullptr;
    }
    return eps->get_application_state_ptr(appstate);
}

sstring gossiper::get_application_state_value(inet_address endpoint, application_state appstate) const {
    auto v = get_application_state_ptr(endpoint, appstate);
    if (!v) {
        return {};
    }
    return v->value;
}

/**
 * This method is used to mark a node as shutdown; that is it gracefully exited on its own and told us about it
 * @param endpoint endpoint that has shut itself down
 */
// Runs inside seastar::async context
void gossiper::mark_as_shutdown(const inet_address& endpoint) {
    auto es = get_endpoint_state_for_endpoint_ptr(endpoint);
    if (es) {
        auto& ep_state = *es;
        ep_state.add_application_state(application_state::STATUS, versioned_value::shutdown(true));
        ep_state.get_heart_beat_state().force_highest_possible_version_unsafe();
        replicate(endpoint, ep_state).get();
        mark_dead(endpoint, ep_state);
        fd().force_conviction(endpoint);
    }
}

void gossiper::force_newer_generation() {
    auto es = get_endpoint_state_for_endpoint_ptr(get_broadcast_address());
    if (es) {
        es->get_heart_beat_state().force_newer_generation_unsafe();
    }
}

static std::string_view do_get_gossip_status(const gms::versioned_value* app_state) noexcept {
    if (!app_state) {
        return gms::versioned_value::STATUS_UNKNOWN;
    }
    const auto& value = app_state->value;
    auto pos = value.find(',');
    if (!value.size() || !pos) {
        return gms::versioned_value::STATUS_UNKNOWN;
    }
    if (pos == sstring::npos) {
        return std::string_view(value);
    }
    return std::string_view(value.data(), pos);
}

std::string_view gossiper::get_gossip_status(const endpoint_state& ep_state) const noexcept {
    return do_get_gossip_status(ep_state.get_application_state_ptr(application_state::STATUS));
}

std::string_view gossiper::get_gossip_status(const inet_address& endpoint) const noexcept {
    return do_get_gossip_status(get_application_state_ptr(endpoint, application_state::STATUS));
}

future<> gossiper::wait_for_gossip(std::chrono::milliseconds initial_delay, std::optional<int32_t> force_after) {
    static constexpr std::chrono::milliseconds GOSSIP_SETTLE_MIN_WAIT_MS{5000};
    static constexpr std::chrono::milliseconds GOSSIP_SETTLE_POLL_INTERVAL_MS{1000};
    static constexpr int32_t GOSSIP_SETTLE_POLL_SUCCESSES_REQUIRED = 3;

    return seastar::async([this, initial_delay, force_after] {
        int32_t total_polls = 0;
        int32_t num_okay = 0;
        int32_t ep_size = endpoint_state_map.size();

        auto delay = initial_delay;

        sleep_abortable(GOSSIP_SETTLE_MIN_WAIT_MS, _abort_source).get();
        while (num_okay < GOSSIP_SETTLE_POLL_SUCCESSES_REQUIRED) {
            sleep_abortable(delay, _abort_source).get();
            delay = GOSSIP_SETTLE_POLL_INTERVAL_MS;

            int32_t current_size = endpoint_state_map.size();
            total_polls++;
            if (current_size == ep_size && _msg_processing == 0) {
                logger.debug("Gossip looks settled");
                num_okay++;
            } else {
                logger.info("Gossip not settled after {} polls.", total_polls);
                num_okay = 0;
            }
            ep_size = current_size;
            if (force_after && *force_after > 0 && total_polls > *force_after) {
                logger.warn("Gossip not settled but startup forced by skip_wait_for_gossip_to_settle. Gossp total polls: {}", total_polls);
                break;
            }
        }
        if (total_polls > GOSSIP_SETTLE_POLL_SUCCESSES_REQUIRED) {
            logger.info("Gossip settled after {} extra polls; proceeding", total_polls - GOSSIP_SETTLE_POLL_SUCCESSES_REQUIRED);
        } else {
            logger.info("No gossip backlog; proceeding");
        }
    });
}

future<> gossiper::wait_for_gossip_to_settle() {
    static constexpr std::chrono::milliseconds GOSSIP_SETTLE_MIN_WAIT_MS{5000};
    auto force_after = _cfg.skip_wait_for_gossip_to_settle();
    auto do_enable_features = [this] {
        return async([this] {
            if (!std::exchange(_gossip_settled, true)) {
               maybe_enable_features();
            }
        });
    };
    if (force_after == 0) {
        return do_enable_features();
    }
    return wait_for_gossip(GOSSIP_SETTLE_MIN_WAIT_MS, force_after).then([this, do_enable_features] {
        return do_enable_features();
    });
}

future<> gossiper::wait_for_range_setup() {
    logger.info("Waiting for pending range setup...");
    auto ring_delay = std::chrono::milliseconds(_cfg.ring_delay_ms());
    return wait_for_gossip(ring_delay);
}

bool gossiper::is_safe_for_bootstrap(inet_address endpoint) {
    // We allow to bootstrap a new node in only two cases:
    // 1) The node is a completely new node and no state in gossip at all
    // 2) The node has state in gossip and it is already removed from the
    // cluster either by nodetool decommission or nodetool removenode
    auto* eps = get_endpoint_state_for_endpoint_ptr(endpoint);
    bool allowed = true;
    if (!eps) {
        logger.debug("is_safe_for_bootstrap: node={}, status=no state in gossip, allowed_to_bootstrap={}", endpoint, allowed);
        return allowed;
    }
    auto status = get_gossip_status(*eps);
    std::unordered_set<std::string_view> allowed_statuses{
        versioned_value::STATUS_LEFT,
        versioned_value::REMOVED_TOKEN,
    };
    allowed = allowed_statuses.contains(status);
    logger.debug("is_safe_for_bootstrap: node={}, status={}, allowed_to_bootstrap={}", endpoint, status, allowed);
    return allowed;
}

std::set<sstring> to_feature_set(sstring features_string) {
    std::set<sstring> features;
    boost::split(features, features_string, boost::is_any_of(","));
    features.erase("");
    return features;
}

std::set<sstring> gossiper::get_supported_features(inet_address endpoint) const {
    auto app_state = get_application_state_ptr(endpoint, application_state::SUPPORTED_FEATURES);
    if (!app_state) {
        return {};
    }
    return to_feature_set(app_state->value);
}

std::set<sstring> gossiper::get_supported_features(const std::unordered_map<gms::inet_address, sstring>& loaded_peer_features, ignore_features_of_local_node ignore_local_node) const {
    std::unordered_map<gms::inet_address, std::set<sstring>> features_map;
    std::set<sstring> common_features;

    for (auto& x : loaded_peer_features) {
        auto features = to_feature_set(x.second);
        if (features.empty()) {
            logger.warn("Loaded empty features for peer node {}", x.first);
        } else {
            features_map.emplace(x.first, std::move(features));
        }
    }

    for (auto& x : endpoint_state_map) {
        auto endpoint = x.first;
        auto features = get_supported_features(endpoint);
        if (ignore_local_node && endpoint == get_broadcast_address()) {
            logger.debug("Ignore SUPPORTED_FEATURES of local node: features={}", features);
            continue;
        }
        if (features.empty()) {
            auto it = loaded_peer_features.find(endpoint);
            if (it != loaded_peer_features.end()) {
                logger.info("Node {} does not contain SUPPORTED_FEATURES in gossip, using features saved in system table, features={}", endpoint, to_feature_set(it->second));
            } else {
                logger.warn("Node {} does not contain SUPPORTED_FEATURES in gossip or system table", endpoint);
            }
        } else {
            // Replace the features with live info
            features_map[endpoint] = std::move(features);
        }
    }

    if (ignore_local_node) {
        features_map.erase(get_broadcast_address());
    }

    if (!features_map.empty()) {
        common_features = features_map.begin()->second;
    }

    for (auto& x : features_map) {
        auto& features = x.second;
        std::set<sstring> result;
        std::set_intersection(features.begin(), features.end(),
                common_features.begin(), common_features.end(),
                std::inserter(result, result.end()));
        common_features = std::move(result);
    }
    common_features.erase("");
    return common_features;
}

void gossiper::check_knows_remote_features(std::set<std::string_view>& local_features, const std::unordered_map<inet_address, sstring>& loaded_peer_features) const {
    auto local_endpoint = get_broadcast_address();
    auto common_features = get_supported_features(loaded_peer_features, ignore_features_of_local_node::yes);
    if (boost::range::includes(local_features, common_features)) {
        logger.info("Feature check passed. Local node {} features = {}, Remote common_features = {}",
                local_endpoint, local_features, common_features);
    } else {
        throw std::runtime_error(format("Feature check failed. This node can not join the cluster because it does not understand the feature. Local node {} features = {}, Remote common_features = {}", local_endpoint, local_features, common_features));
    }
}

void gossiper::check_snitch_name_matches() const {
    const auto& my_snitch_name = locator::i_endpoint_snitch::get_local_snitch_ptr()->get_name();
    for (const auto& [address, state] : endpoint_state_map) {
        const auto remote_snitch_name = state.get_application_state_ptr(application_state::SNITCH_NAME);
        if (!remote_snitch_name) {
            continue;
        }

        if (remote_snitch_name->value != my_snitch_name) {
            throw std::runtime_error(format("Snitch check failed. This node cannot join the cluster because it uses {} and not {}", my_snitch_name, remote_snitch_name->value));
        }
    }
}

sstring gossiper::get_all_endpoint_states() {
    std::stringstream ss;
    for (auto& entry : endpoint_state_map) {
        auto& ep = entry.first;
        auto& state = entry.second;
        ss << ep << "\n";
        append_endpoint_state(ss, state);
    }
    return sstring(ss.str());
}

std::map<sstring, sstring> gossiper::get_simple_states() {
    std::map<sstring, sstring> nodes_status;
    for (auto& entry : endpoint_state_map) {
        auto& ep = entry.first;
        auto& state = entry.second;
        std::stringstream ss;
        ss << ep;

        if (state.is_alive()) {
            nodes_status.emplace(sstring(ss.str()), "UP");
        } else {
            nodes_status.emplace(sstring(ss.str()), "DOWN");
        }
    }
    return nodes_status;
}

int gossiper::get_down_endpoint_count() const noexcept {
    return endpoint_state_map.size() - get_up_endpoint_count();
}

int gossiper::get_up_endpoint_count() const noexcept {
    return boost::count_if(endpoint_state_map | boost::adaptors::map_values, std::mem_fn(&endpoint_state::is_alive));
}

sstring gossiper::get_endpoint_state(sstring address) {
    std::stringstream ss;
    auto* eps = get_endpoint_state_for_endpoint_ptr(inet_address(address));
    if (eps) {
        append_endpoint_state(ss, *eps);
        return sstring(ss.str());
    } else {
        return sstring("unknown endpoint ") + address;
    }
}

void gossiper::append_endpoint_state(std::stringstream& ss, const endpoint_state& state) {
    ss << "  generation:" << state.get_heart_beat_state().get_generation() << "\n";
    ss << "  heartbeat:" << state.get_heart_beat_state().get_heart_beat_version() << "\n";
    for (const auto& entry : state.get_application_state_map()) {
        auto& app_state = entry.first;
        auto& versioned_val = entry.second;
        if (app_state == application_state::TOKENS) {
            continue;
        }
        ss << "  " << app_state << ":" << versioned_val.version << ":" << versioned_val.value << "\n";
    }
    const auto& app_state_map = state.get_application_state_map();
    if (app_state_map.contains(application_state::TOKENS)) {
        ss << "  TOKENS:" << app_state_map.at(application_state::TOKENS).version << ":<hidden>\n";
    } else {
        ss << "  TOKENS: not present" << "\n";
    }
}

// Runs inside seastar::async context
void gossiper::maybe_enable_features() {
    if (!_gossip_settled) {
        return;
    }
    auto loaded_peer_features = db::system_keyspace::load_peer_features().get0();
    auto&& features = get_supported_features(loaded_peer_features, ignore_features_of_local_node::no);
    container().invoke_on_all([&features] (gossiper& g) {
        for (auto&& name : features) {
            g._feature_service.enable(name);
        }
        g._features_condvar.broadcast();
    }).get();
}

locator::token_metadata_ptr gossiper::get_token_metadata_ptr() const noexcept {
    return _shared_token_metadata.get();
}

} // namespace gms
