Process connection attempts in a round-robin fashion in order to load-balance connection attempts.

# Conflicts:
#	nano/node/network.cpp

nano/lib/config.hpp

@@ -202,6 +202,7 @@ public:
 		default_websocket_port (47000),
 		aec_loop_interval_ms (300), // Update AEC ~3 times per second
 		cleanup_period (default_cleanup_period),
+		merge_period (std::chrono::milliseconds (250)),
 		keepalive_period (std::chrono::seconds (15)),
 		idle_timeout (default_cleanup_period * 2),
 		silent_connection_tolerance_time (std::chrono::seconds (120)),
@@ -239,6 +240,7 @@ public:
 		{
 			aec_loop_interval_ms = 20;
 			cleanup_period = std::chrono::seconds (1);
+			merge_period = std::chrono::milliseconds (10);
 			keepalive_period = std::chrono::seconds (1);
 			idle_timeout = cleanup_period * 15;
 			max_peers_per_ip = 20;
@@ -277,6 +279,8 @@ public:
 	{
 		return cleanup_period * 5;
 	}
+	/** How often to connect to other peers */
+	std::chrono::milliseconds merge_period;
 	/** How often to send keepalive messages */
 	std::chrono::seconds keepalive_period;
 	/** Default maximum idle time for a socket before it's automatically closed */

nano/node/network.cpp

@@ -239,8 +239,6 @@ public:
 
 	void keepalive (nano::keepalive const & message_a) override
 	{
-		node.network.merge_peers (message_a.peers);
-
 		// Check for special node port data
 		auto peer0 (message_a.peers[0]);
 		if (peer0.address () == boost::asio::ip::address_v6{} && peer0.port () != 0)

nano/node/transport/channel.hpp

@@ -187,4 +187,4 @@ struct hash<std::reference_wrapper<::nano::transport::channel const>>
 		return hash (channel_a.get ());
 	}
 };
-}
+}

nano/node/transport/tcp.cpp

@@ -357,6 +357,7 @@ void nano::transport::tcp_channels::process_message (nano::message const & messa
 void nano::transport::tcp_channels::start ()
 {
 	ongoing_keepalive ();
+	ongoing_merge (0);
 }
 
 void nano::transport::tcp_channels::stop ()
@@ -509,6 +510,77 @@ void nano::transport::tcp_channels::ongoing_keepalive ()
 	});
 }
 
+void nano::transport::tcp_channels::ongoing_merge (size_t channel_index)
+{
+	nano::unique_lock<nano::mutex> lock{ mutex };
+	std::optional<nano::keepalive> keepalive;
+	size_t count = 0;
+	while (!keepalive && channels.size () > 0 && count++ < channels.size ())
+	{
+		++channel_index;
+		if (channels.size () <= channel_index)
+		{
+			channel_index = 0;
+		}
+		auto server = channels.get<random_access_tag> ()[channel_index].response_server;
+		if (server && server->last_keepalive)
+		{
+			keepalive = std::move (server->last_keepalive);
+			server->last_keepalive = std::nullopt;
+		}
+	}
+	lock.unlock ();
+	if (keepalive)
+	{
+		ongoing_merge (channel_index, *keepalive, 1);
+	}
+	else
+	{
+		std::weak_ptr<nano::node> node_w = node.shared ();
+		node.workers.add_timed_task (std::chrono::steady_clock::now () + node.network_params.network.merge_period, [node_w, channel_index] () {
+			if (auto node_l = node_w.lock ())
+			{
+				if (!node_l->network.tcp_channels.stopped)
+				{
+					node_l->network.tcp_channels.ongoing_merge (channel_index);
+				}
+			}
+		});
+	}
+}
+
+void nano::transport::tcp_channels::ongoing_merge (size_t channel_index, nano::keepalive keepalive, size_t peer_index)
+{
+	debug_assert (peer_index < keepalive.peers.size ());
+	node.network.merge_peer (keepalive.peers[peer_index++]);
+	if (peer_index < keepalive.peers.size ())
+	{
+		std::weak_ptr<nano::node> node_w = node.shared ();
+		node.workers.add_timed_task (std::chrono::steady_clock::now () + node.network_params.network.merge_period, [node_w, channel_index, keepalive, peer_index] () {
+			if (auto node_l = node_w.lock ())
+			{
+				if (!node_l->network.tcp_channels.stopped)
+				{
+					node_l->network.tcp_channels.ongoing_merge (channel_index, keepalive, peer_index);
+				}
+			}
+		});
+	}
+	else
+	{
+		std::weak_ptr<nano::node> node_w = node.shared ();
+		node.workers.add_timed_task (std::chrono::steady_clock::now () + node.network_params.network.merge_period, [node_w, channel_index] () {
+			if (auto node_l = node_w.lock ())
+			{
+				if (!node_l->network.tcp_channels.stopped)
+				{
+					node_l->network.tcp_channels.ongoing_merge (channel_index);
+				}
+			}
+		});
+	}
+}
+
 void nano::transport::tcp_channels::list (std::deque<std::shared_ptr<nano::transport::channel>> & deque_a, uint8_t minimum_version_a, bool include_temporary_channels_a)
 {
 	nano::lock_guard<nano::mutex> lock{ mutex };

nano/node/transport/tcp.hpp

@@ -128,6 +128,8 @@ namespace transport
 		std::unique_ptr<container_info_component> collect_container_info (std::string const &);
 		void purge (std::chrono::steady_clock::time_point const &);
 		void ongoing_keepalive ();
+		void ongoing_merge (size_t channel_index);
+		void ongoing_merge (size_t channel_index, nano::keepalive keepalive, size_t peer_index);
 		void list (std::deque<std::shared_ptr<nano::transport::channel>> &, uint8_t = 0, bool = true);
 		void modify (std::shared_ptr<nano::transport::channel_tcp> const &, std::function<void (std::shared_ptr<nano::transport::channel_tcp> const &)>);
 		void update (nano::tcp_endpoint const &);

nano/node/transport/tcp_server.cpp

@@ -623,6 +623,7 @@ nano::transport::tcp_server::realtime_message_visitor::realtime_message_visitor
 void nano::transport::tcp_server::realtime_message_visitor::keepalive (const nano::keepalive & message)
 {
 	process = true;
+	server.set_last_keepalive (message);
 }
 
 void nano::transport::tcp_server::realtime_message_visitor::publish (const nano::publish & message)
@@ -786,6 +787,15 @@ void nano::transport::tcp_server::timeout ()
 	}
 }
 
+void nano::transport::tcp_server::set_last_keepalive (nano::keepalive const & message)
+{
+	std::lock_guard<nano::mutex> lock{ mutex };
+	if (!last_keepalive)
+	{
+		last_keepalive = message;
+	}
+}
+
 bool nano::transport::tcp_server::to_bootstrap_connection ()
 {
 	auto node = this->node.lock ();

nano/node/transport/tcp_server.hpp

@@ -62,6 +62,7 @@ public:
 	void stop ();
 
 	void timeout ();
+	void set_last_keepalive (nano::keepalive const & message);
 
 	std::shared_ptr<nano::transport::socket> const socket;
 	std::weak_ptr<nano::node> const node;
@@ -72,6 +73,7 @@ public:
 	nano::tcp_endpoint remote_endpoint{ boost::asio::ip::address_v6::any (), 0 };
 	nano::account remote_node_id{};
 	std::chrono::steady_clock::time_point last_telemetry_req{};
+	std::optional<nano::keepalive> last_keepalive;
 
 private:
 	void send_handshake_response (nano::node_id_handshake::query_payload const & query, bool v2);