start implementing k-choices rebalancing, considering 1 VS each run

only loop implemented, rebalancing not implemented

app/Main.hs

@@ -31,6 +31,7 @@ readConfig = do
     -- waiting for timeout
     let
         speedup = read speedupString
+        statsEvalD = 120 * 10^6 `div` speedup
         confBootstrapNodes' = case remainingArgs of
             bootstrapHost : bootstrapPortString : _ ->
                 [(bootstrapHost, read bootstrapPortString)]
@@ -52,6 +53,7 @@ readConfig = do
           , confKChoicesOverload = 0.9
           , confKChoicesUnderload = 0.1
           , confKChoicesMaxVS = 8
+          , confKChoicesRebalanceInterval = round  (realToFrac statsEvalD * 1.1 :: Double)
           }
         sConf = ServiceConf
           { confSubscriptionExpiryTime = 24*3600 / fromIntegral speedup
@@ -59,7 +61,7 @@ readConfig = do
           , confServiceHost = confDomainString
           , confLogfilePath = "../simulationData/logs/" <> confDomainString <> ".log"
           , confSpeedupFactor = speedup
-          , confStatsEvalDelay = 120 * 10^6 `div` speedup
+          , confStatsEvalDelay = statsEvalD
           }
     pure (fConf, sConf)
 

src/Hash2Pub/FediChord.hs

@@ -322,6 +322,34 @@ kChoicesDepartureCost remainingOwnLoad ownCap thisSegmentLoad segment =
   + abs (remainingOwnLoad + thisSegmentLoad) / ownCap
   - abs (segmentOwnerRemainingLoadTarget segment) / segmentOwnerCapacity segment
 
+
+kChoicesRebalanceThread :: (Service s (RealNodeSTM s)) => RealNodeSTM s -> IO ()
+kChoicesRebalanceThread nodeSTM = (confKChoicesRebalanceInterval . nodeConfig <$> readTVarIO nodeSTM) >>= rebalanceVS 0
+  where
+      rebalanceVS :: NodeID -> Int -> IO ()
+      rebalanceVS startAt interval = do
+          threadDelay interval
+          (vsToRebalance', serv) <- atomically $ do
+              node <- readTVar nodeSTM
+              pure (rMapLookupPred 0 (vservers node), nodeService node)
+          maybe
+            -- wait and retry if no active VS available
+            (rebalanceVS startAt interval)
+            (\(vsNid, vsSTM) -> do
+              vs <- readTVarIO vsSTM
+              -- query neighbour node(s) load
+              -- query own load
+              -- calculate departure cost
+              -- if deciding to re-balance, first leave and then join
+              -- loop
+              rebalanceVS vsNid interval
+              )
+              vsToRebalance'
+
+
+          -- placeholder
+          pure ()
+
 -- | Join a new node into the DHT, using a provided bootstrap node as initial cache seed
 -- for resolving the new node's position.
 fediChordBootstrapJoin :: Service s (RealNodeSTM s)

src/Hash2Pub/FediChordTypes.hs

@@ -459,6 +459,8 @@ data FediChordConf = FediChordConf
     -- ^ fraction of capacity below which a node considers itself underloaded
     , confKChoicesMaxVS             :: Word8
     -- ^ upper limit of vserver index κ
+    , confKChoicesRebalanceInterval :: Int
+    -- ^ interval between vserver rebalance attempts
     }
     deriving (Show, Eq)