Increase discovery message interval, distribute messages

Previously on large server(s), there was an issue where because
chunkloaded computers all started up at once, so they all had the same
discovery message sending timer. This prevents that by starting each off
with a random offset. Also increases the interval for sending messages
from 15 s to 30 s, so that messages (which are the same, a lot of the
time) get sent less often.

sys/apps/network/snmp.lua

@@ -152,7 +152,7 @@ local function getSlots()
 end
 
 local function sendInfo()
-	if os.clock() - infoTimer >= 1 then -- don't flood
+	if os.clock() - infoTimer >= 5 then -- don't flood
 		infoTimer = os.clock()
 		info.label = os.getComputerLabel()
 		info.uptime = math.floor(os.clock())
@@ -194,16 +194,25 @@ local function sendInfo()
 	end
 end
 
--- every 10 seconds, send out this computer's info
-Event.onInterval(10, function()
-	sendInfo()
+local function cleanNetwork()
 	for _,c in pairs(_G.network) do
 		local elapsed = os.clock()-c.timestamp
-		if c.active and elapsed > 15 then
+		if c.active and elapsed > 90 then
 			c.active = false
 			os.queueEvent('network_detach', c)
 		end
 	end
+end
+
+-- every 60 seconds, send out this computer's info
+-- send with offset so that messages are evenly distributed and do not all come at once
+Event.onTimeout(math.random() * 60, function()
+	sendInfo()
+	cleanNetwork()
+	Event.onInterval(60, function()
+		sendInfo()
+		cleanNetwork()
+	end)
 end)
 
 Event.on('turtle_response', function()
@@ -213,4 +222,5 @@ Event.on('turtle_response', function()
 	end
 end)
 
-Event.onTimeout(1, sendInfo)
+-- send info early so that computers show soon after booting
+Event.onTimeout(math.random() * 4 + 1, sendInfo)