test: raft: randomized_nemesis_test: remove old failure_detector

No longer used.
Split from the previous commit for a better diff.

test/raft/randomized_nemesis_test.cc

@@ -985,80 +985,6 @@ public:
     }
 };
 
-// A failure detector using heartbeats for deciding whether to convict a server
-// as failed. We convict a server if we don't receive a heartbeat for a long enough time.
-// `failure_detector` assumes a message-passing method given by a `send_heartbeat_t` function
-// through the constructor for sending heartbeats and assumes that `receive_heartbeat` is called
-// whenever another server sends a message to us.
-// To decide who to send heartbeats to we use the ``current knowledge'' of servers in the network
-// which is updated through `add_server` and `remove_server` functions.
-class failure_detector : public raft::failure_detector {
-public:
-    using send_heartbeat_t = std::function<void(raft::server_id dst)>;
-
-private:
-    raft::logical_clock _clock;
-
-    // The set of known servers, used to broadcast heartbeats.
-    std::unordered_set<raft::server_id> _known;
-
-    // The last time we received a heartbeat from a server.
-    std::unordered_map<raft::server_id, raft::logical_clock::time_point> _last_heard;
-
-    // The last time we sent a heartbeat.
-    raft::logical_clock::time_point _last_beat;
-
-    // How long from the last received heartbeat does it take to convict a node as dead.
-    const raft::logical_clock::duration _convict_threshold;
-
-    send_heartbeat_t _send_heartbeat;
-
-public:
-    failure_detector(raft::logical_clock::duration convict_threshold, send_heartbeat_t f)
-        : _convict_threshold(convict_threshold), _send_heartbeat(std::move(f))
-    {
-        send_heartbeats();
-        assert(_last_beat == _clock.now());
-    }
-
-    void receive_heartbeat(raft::server_id src) {
-        assert(_known.contains(src));
-        _last_heard[src] = std::max(_clock.now(), _last_heard[src]);
-    }
-
-    void tick() {
-        _clock.advance();
-
-        // TODO: make it adjustable
-        static const raft::logical_clock::duration _heartbeat_period = 10_t;
-
-        if (_last_beat + _heartbeat_period <= _clock.now()) {
-            send_heartbeats();
-        }
-    }
-
-    void send_heartbeats() {
-        for (auto& dst : _known) {
-            _send_heartbeat(dst);
-        }
-        _last_beat = _clock.now();
-    }
-
-    // We expect a server to be added through this function before we receive a heartbeat from it.
-    void add_server(raft::server_id id) {
-        _known.insert(id);
-    }
-
-    void remove_server(raft::server_id id) {
-        _known.erase(id);
-        _last_heard.erase(id);
-    }
-
-    bool is_alive(raft::server_id id) override {
-        return _clock.now() < _last_heard[id] + _convict_threshold;
-    }
-};
-
 // Maps `direct_failure_detector::pinger::endpoint_id`s to `raft::server_id`s.
 // We only need to store the map on shard 0, since all `failure_detector` RPCs will be routed through shard 0 (for simplicity of implementation).
 class direct_fd_endpoint_map {