Bring back low priority block events in a safe way. (#16945)

This reverts commit 6ac8346, and brings back low priority block events.
(Revert "Revert part of 16013 - restore liquid updates to the client (#16663)")

Close block changes are never considered "low priority"

Author: lhofhansl

src/map.h

@@ -46,6 +46,9 @@ struct MapEditEvent
 	MapNode n = CONTENT_AIR;
 	std::vector<v3s16> modified_blocks; // Represents a set
 	bool is_private_change = false;
+	// Setting low_priority to true allows the server
+	// to send this change to clients with some delay.
+	bool low_priority = false;
 
 	MapEditEvent() = default;
 

src/server.cpp

@@ -784,6 +784,7 @@ void Server::AsyncRunStep(float dtime, bool initial_step)
 		if (!modified_blocks.empty()) {
 			MapEditEvent event;
 			event.type = MEET_OTHER;
+			event.low_priority = true;
 			event.setModifiedBlocks(modified_blocks);
 			m_env->getMap().dispatchEvent(event);
 		}
@@ -1041,7 +1042,7 @@ void Server::AsyncRunStep(float dtime, bool initial_step)
 			}
 			case MEET_OTHER:
 				prof.add("MEET_OTHER", 1);
-				m_clients.markBlocksNotSent(event->modified_blocks);
+				m_clients.markBlocksNotSent(event->modified_blocks, event->low_priority);
 				break;
 			default:
 				prof.add("unknown", 1);
@@ -1057,7 +1058,7 @@ void Server::AsyncRunStep(float dtime, bool initial_step)
 			*/
 			for (const u16 far_player : far_players) {
 				if (RemoteClient *client = getClient(far_player))
-					client->SetBlocksNotSent(event->modified_blocks);
+					client->SetBlocksNotSent(event->modified_blocks, event->low_priority);
 			}
 
 			delete event;

src/server/clientiface.cpp

@@ -430,7 +430,7 @@ void RemoteClient::SentBlock(v3s16 p)
 				" already in m_blocks_sending"<<std::endl;
 }
 
-void RemoteClient::SetBlockNotSent(v3s16 p)
+void RemoteClient::SetBlockNotSent(v3s16 p, bool low_priority)
 {
 	m_nothing_to_send_pause_timer = 0;
 
@@ -446,14 +446,19 @@ void RemoteClient::SetBlockNotSent(v3s16 p)
 		// will reset m_nearest_unsent_d to 0 anyway (see getNextBlocks).
 		p -= m_last_center;
 		s16 this_d = std::max({std::abs(p.X), std::abs(p.Y), std::abs(p.Z)});
-		m_nearest_unsent_d = std::min(m_nearest_unsent_d, this_d);
+
+		// If this is a low priority event (and not close), do not reset m_nearest_unsent_d.
+		// Instead, the send loop will get to the block in the next full loop iteration.
+		if (!low_priority || this_d < m_block_cull_optimize_distance) {
+			m_nearest_unsent_d = std::min(m_nearest_unsent_d, this_d);
+		}
 	}
 }
 
-void RemoteClient::SetBlocksNotSent(const std::vector<v3s16> &blocks)
+void RemoteClient::SetBlocksNotSent(const std::vector<v3s16> &blocks, bool low_priority)
 {
 	for (v3s16 p : blocks) {
-		SetBlockNotSent(p);
+		SetBlockNotSent(p, low_priority);
 	}
 }
 
@@ -677,12 +682,12 @@ std::vector<session_t> ClientInterface::getClientIDs(ClientState min_state)
 	return reply;
 }
 
-void ClientInterface::markBlocksNotSent(const std::vector<v3s16> &positions)
+void ClientInterface::markBlocksNotSent(const std::vector<v3s16> &positions, bool low_priority)
 {
 	RecursiveMutexAutoLock clientslock(m_clients_mutex);
 	for (const auto &client : m_clients) {
 		if (client.second->getState() >= CS_Active)
-			client.second->SetBlocksNotSent(positions);
+			client.second->SetBlocksNotSent(positions, low_priority);
 	}
 }
 

src/server/clientiface.h

@@ -250,8 +250,8 @@ class RemoteClient
 
 	void SentBlock(v3s16 p);
 
-	void SetBlockNotSent(v3s16 p);
-	void SetBlocksNotSent(const std::vector<v3s16> &blocks);
+	void SetBlockNotSent(v3s16 p, bool low_priority = false);
+	void SetBlocksNotSent(const std::vector<v3s16> &blocks, bool low_priority = false);
 
 	/**
 	 * tell client about this block being modified right now.
@@ -442,7 +442,7 @@ class ClientInterface {
 	std::vector<session_t> getClientIDs(ClientState min_state=CS_Active);
 
 	/* mark blocks as not sent on all active clients */
-	void markBlocksNotSent(const std::vector<v3s16> &positions);
+	void markBlocksNotSent(const std::vector<v3s16> &positions, bool low_priority = false);
 
 	/* verify if server user limit was reached */
 	bool isUserLimitReached();

src/servermap.cpp

@@ -778,6 +778,7 @@ MapBlock *ServerMap::loadBlock(const std::string &blob, v3s16 p3d, bool save_aft
 		if (!modified_blocks.empty()) {
 			MapEditEvent event;
 			event.type = MEET_OTHER;
+			event.low_priority = true;
 			event.setModifiedBlocks(modified_blocks);
 			dispatchEvent(event);
 		}