rewrite parts of the teleportation tube to avoid a few grave performance issues:

* don't forceload the block of every single tube in the world on every item being send through any one of them
* cache file contents to avoid unnecessary reads on every single item send through a tp tube
* reduce redundant metadata and table lookups
* reduce write operations during the same changes to a file

still to do is a switch from an arraylist-table to a hashmap-table to make lookups and updates on the cache faster

teleport_tube.lua

@@ -1,53 +1,59 @@
-
 local filename=minetest.get_worldpath() .. "/teleport_tubes"
 
-local function read_file()
+local tp_tube_db = nil -- nil forces a read
-	local f = io.open(filename, "r")
+
-	if f == nil then return {} end
+local function read_tube_db()
-    	local t = f:read("*all")
+	local file = io.open(filename, "r")
-    	f:close()
+	if file ~= nil then
-	if t == "" or t == nil then return {} end
+		local file_content = file:read("*all")
-	return minetest.deserialize(t)
+		io.close(file)
+
+		if file_content and file_content ~= "" then
+			tp_tube_db = minetest.deserialize(file_content)
+			return tp_tube_db-- we read sucessfully
+		end
+	end
+	tp_tube_db = {}
+	return tp_tube_db
 end
 
-local function write_file(tbl)
+local function save_tube_db()
-	local f = io.open(filename, "w")
+	local file, err = io.open(filename, "w")
-    	f:write(minetest.serialize(tbl))
+	if file then
-    	f:close()
+		file:write(minetest.serialize(tp_tube_db))
+		io.close(file)
+	else
+		error(err)
+	end
 end
 
-local function update_pos_in_file(pos)
+-- updates or adds a tube
-	local tbl=read_file()
+local function set_tube(pos, channel, can_receive)
-	for _, val in ipairs(tbl) do
+	local tubes = tp_tube_db or read_tube_db()
+	for _, val in ipairs(tubes) do
 		if val.x == pos.x and val.y == pos.y and val.z == pos.z then
-			local meta = minetest.get_meta(val)
+			val.channel = channel
-			val.channel = meta:get_string("channel")
+			val.cr = can_receive
-			val.cr = meta:get_int("can_receive")
+			save_tube_db()
-		end
-	end
-	write_file(tbl)
-end
-
-local function add_tube_in_file(pos,channel, cr)
-	local tbl=read_file()
-	for _,val in ipairs(tbl) do
-		if val.x==pos.x and val.y==pos.y and val.z==pos.z then
 			return
 		end
 	end
-	table.insert(tbl,{x=pos.x,y=pos.y,z=pos.z,channel=channel,cr=cr})
+
-	write_file(tbl)
+	-- we haven't found any tp tube to update, so lets add it
+	table.insert(tp_tube_db,{x=pos.x,y=pos.y,z=pos.z,channel=channel,cr=cr})
+	save_tube_db()
 end
 
-local function remove_tube_in_file(pos)
+local function remove_tube(pos)
-	local tbl = read_file()
+	local tubes = tp_tube_db or read_tube_db()
 	local newtbl = {}
-	for _, val in ipairs(tbl) do
+	for _, val in ipairs(tubes) do
 		if val.x ~= pos.x or val.y ~= pos.y or val.z ~= pos.z then
 			table.insert(newtbl, val)
 		end
 	end
-	write_file(newtbl)
+	tp_tube_db = newtbl
+	save_tube_db()
 end
 
 local function read_node_with_vm(pos)
@@ -58,39 +64,35 @@ local function read_node_with_vm(pos)
 	return minetest.get_name_from_content_id(data[area:index(pos.x, pos.y, pos.z)])
 end
 
-local function get_tubes_in_file(pos,channel)
+local function get_receivers(pos,channel)
-	local tbl = read_file()
+	local tubes = tp_tube_db or read_tube_db()
-	local newtbl = {}
+	local receivers = {}
 	local changed = false
-	for _, val in ipairs(tbl) do
+	for _, val in ipairs(tubes) do
-		local meta = minetest.get_meta(val)
+		-- skip all non-receivers and the tube that it came from as early as possible, as this is called often
-		local name = read_node_with_vm(val)
+		if (val.cr == 1 and val.channel == channel and (val.x ~= pos.x or val.y ~= pos.y or val.z ~= pos.z)) then
 			local is_loaded = (minetest.get_node_or_nil(val) ~= nil)
-		local is_teleport_tube = minetest.registered_nodes[name] and minetest.registered_nodes[name].is_teleport_tube
+			local node_name = is_loaded and minetest.get_node(pos).name or read_node_with_vm(val)
-		if is_teleport_tube then
+
-			if is_loaded and (val.channel ~= meta:get_string("channel") or val.cr ~= meta:get_int("can_receive")) then
+			if minetest.registered_nodes[node_name] and minetest.registered_nodes[node_name].is_teleport_tube then
-				val.channel = meta:get_string("channel")
+				table.insert(receivers, val)
-				val.cr = meta:get_int("can_receive")
-				changed = true
-			end
-			if val.cr == 1 and val.channel == channel and (val.x ~= pos.x or val.y ~= pos.y or val.z ~= pos.z) then
-				table.insert(newtbl, val)
-			end
 			else
 				val.to_remove = true
 				changed = true
 			end
 		end
+	end
 	if changed then
 		local updated = {}
-		for _, val in ipairs(tbl) do
+		for _, val in ipairs(tubes) do
 			if not val.to_remove then
 				table.insert(updated, val)
 			end
 		end
-		write_file(updated)
+		tp_tube_db = updated
+		save_tube_db()
 	end
-	return newtbl
+	return receivers
 end
 
 local teleport_noctr_textures={"pipeworks_teleport_tube_noctr.png","pipeworks_teleport_tube_noctr.png","pipeworks_teleport_tube_noctr.png",
@@ -102,8 +104,8 @@ local teleport_end_textures={"pipeworks_teleport_tube_end.png","pipeworks_telepo
 local teleport_short_texture="pipeworks_teleport_tube_short.png"
 local teleport_inv_texture="pipeworks_teleport_tube_inv.png"
 
-local function set_teleport_tube_formspec(meta)
+local function set_teleport_tube_formspec(meta, can_receive)
-	local cr = meta:get_int("can_receive") ~= 0
+	local cr = (can_receive ~= 0)
 	meta:set_string("formspec","size[10.5,1;]"..
 			"field[0,0.5;7,1;channel;Channel:;${channel}]"..
 			"button[8,0;2.5,1;"..(cr and "cr0" or "cr1")..";"..
@@ -120,7 +122,7 @@ pipeworks.register_tube("pipeworks:teleport_tube","Teleporting Pneumatic Tube Se
 			velocity.z = 0
 			local meta = minetest.get_meta(pos)
 			local channel = meta:get_string("channel")
-			local target = get_tubes_in_file(pos,channel)
+			local target = get_receivers(pos, channel)
 			if target[1] == nil then return {} end
 			local d = math.random(1,#target)
 			pos.x = target[d].x
@@ -133,48 +135,57 @@ pipeworks.register_tube("pipeworks:teleport_tube","Teleporting Pneumatic Tube Se
 		local meta = minetest.get_meta(pos)
 		meta:set_string("channel","")
 		meta:set_int("can_receive",1)
-		add_tube_in_file(pos,"")
+		set_tube(pos, "", 1)
-		set_teleport_tube_formspec(meta)
+		set_teleport_tube_formspec(meta, 1)
 	end,
 	on_receive_fields = function(pos,formname,fields,sender)
 		local meta = minetest.get_meta(pos)
+		local can_receive = meta:get_int("can_receive")
 
-		--check for private channels
+		if fields.channel then
-		if fields.channel ~= nil then
+			-- check for private channels
+			local sender_name = sender:get_player_name()
 			local name, mode = fields.channel:match("^([^:;]+)([:;])")
-			if name and mode and name ~= sender:get_player_name() then
+			if name and mode and name ~= sender_name then
-				
 				--channels starting with '[name]:' can only be used by the named player
 				if mode == ":" then
-					minetest.chat_send_player(sender:get_player_name(), "Sorry, channel '"..fields.channel.."' is reserved for exclusive use by "..name)
+					minetest.chat_send_player(sender_name, "Sorry, channel '"..fields.channel.."' is reserved for exclusive use by "..name)
 					return
 				
 				--channels starting with '[name];' can be used by other players, but cannot be received from
-				elseif mode == ";" and (fields.cr1 or (meta:get_int("can_receive") ~= 0 and not fields.cr0)) then
+				elseif mode == ";" and (fields.cr1 or (can_receive ~= 0 and not fields.cr0)) then
-					minetest.chat_send_player(sender:get_player_name(), "Sorry, receiving from channel '"..fields.channel.."' is reserved for "..name)
+					minetest.chat_send_player(sender_name, "Sorry, receiving from channel '"..fields.channel.."' is reserved for "..name)
 					return
 				end
 			end
+			-- save channel if we set one
+			meta:set_string("channel", fields.channel)
+		end
+		-- make sure we have a channel, either the newly set one or the one from metadata
+		local channel = fields.channel or meta:get_string("channel")
+
+		if fields.cr0 and can_receive ~= 0 then
+			can_receive = 0
+			meta:set_int("can_receive", can_receive)
+		elseif fields.cr1 and can_receive ~= 1 then
+			can_receive = 1
+			meta:set_int("can_receive", can_receive)
 		end
 
-		if fields.channel==nil then fields.channel=meta:get_string("channel") end
+		set_tube(pos, fields.channel, can_receive)
-		meta:set_string("channel",fields.channel)
+		set_teleport_tube_formspec(meta, can_receive)
-		remove_tube_in_file(pos)
-		if fields.cr0 then meta:set_int("can_receive", 0) end
-		if fields.cr1 then meta:set_int("can_receive", 1) end
-		local cr = meta:get_int("can_receive")
-		add_tube_in_file(pos, fields.channel, meta:get_int("can_receive"))
-		set_teleport_tube_formspec(meta)
 	end,
 	on_destruct = function(pos)
-		remove_tube_in_file(pos)
+		remove_tube(pos)
-	end})
+	end
+})
 
 if minetest.get_modpath("mesecons_mvps") ~= nil then
 	mesecon.register_on_mvps_move(function(moved_nodes)
 		for _, n in ipairs(moved_nodes) do
 			if string.find(n.node.name, "pipeworks:teleport_tube") ~= nil then
-				update_pos_in_file(n.pos)
+				local meta = minetest.get_meta(n.pos)
+				set_tube(n.pos, meta:get_string("channel"), meta:get_int("can_receive"))
 			end
 		end
 	end)