feat: add global registry actor to system

actors.cabal

@@ -70,6 +70,7 @@ library
       Control.Actor.Core
       Control.Actor.Supervision
       Control.Actor.Network
+      Control.Actor.Registry
 
     -- Modules included in this library but not exported.
     -- other-modules:

src/Control/Actor.hs

@@ -5,10 +5,6 @@ module Control.Actor
   , module Control.Actor.Core
   , module Control.Actor.Supervision
   , module Control.Actor.Network
-  , pass
-  , continue
-  , maybeContinue
-  , become
   -- Demo
   , pingActor
   , forwardActorWithCell
@@ -29,22 +25,26 @@ import Control.Concurrent.STM
   ( TMVar, TVar
   , atomically, newEmptyTMVarIO, newTVarIO, readTMVar, readTVarIO, writeTQueue, writeTVar
   )
-import Control.Monad ((<=<))
+import Control.Monad ((<=<), void)
 import Control.Monad.Reader (MonadIO (..))
 import Unsafe.Coerce (unsafeCoerce)
+import Control.Exception (SomeException, try)
+import Control.Actor.Registry (createRegistry, registerActor, lookupRemoteActor)
 
-continue :: r -> Actor msg u r
-continue x = (\u -> ActorResult (Just x) u Nothing) <$> state
+initRuntime :: NodeAddr -> (NodeAddr -> IO (Transport, NodeAddr)) -> IO Runtime
+initRuntime myAddr createTransport = do
+  (transport, actualAddr) <- createTransport myAddr
+  rt0 <- newRuntime actualAddr transport
+  let rt = rt0 { rtSendRemote = \addr nm -> getOrCreateConn addr >>= cast' nm }
+  withRuntime rt $ void $ spawnActor sysHandlerFn stopOnDeath ()
+  withRuntime rt $ void createRegistry
+  tListen transport $ \ch -> do
+    result <- try @SomeException $ withRuntime rt $ handleNewConn ch
+    case result of
+      Left _   -> chClose ch
+      Right () -> return ()
+  return rt
 
-maybeContinue :: Maybe r -> Actor msg u r
-maybeContinue Nothing = pass
-maybeContinue (Just r) = continue r
-
-pass :: Actor msg u r
-pass = (\u -> ActorResult Nothing u Nothing) <$> state
-
-become :: Handler msg u r -> Actor msg u r
-become fn = (\u -> ActorResult Nothing u (Just fn)) <$> state
 
 -- Demo
 
@@ -70,7 +70,7 @@ repeatActor r cell () = do
 
 system :: IO ()
 system = do
-  rt <- initRuntime (NodeAddr "localhost" 9000)
+  rt <- initRuntime (NodeAddr "localhost" 9000) createTCPTransport
   withRuntime rt $ do
     pingCell    <- liftIO newEmptyTMVarIO
     forwardCell <- liftIO newEmptyTMVarIO
@@ -123,8 +123,8 @@ networkDemo = do
 
   -- Port 0 lets the OS pick a free port each run, avoiding stale-socket
   -- conflicts when re-running in the same GHCi session.
-  rt1 <- initRuntime (NodeAddr "localhost" 0)
-  rt2 <- initRuntime (NodeAddr "localhost" 0)
+  rt1 <- initRuntime (NodeAddr "localhost" 0) createTCPTransport
+  rt2 <- initRuntime (NodeAddr "localhost" 0) createTCPTransport
   let addr1 = rtNodeId rt1
       addr2 = rtNodeId rt2
 
@@ -133,27 +133,27 @@ networkDemo = do
   node2 <- withRuntime rt1 $ connect Nothing addr2
   node1 <- withRuntime rt2 $ connect Nothing addr1
 
-  -- Helper: build a RemoteRef that is visible from one node for an actor
-  -- that was spawned on a different node. The actor's own id uses NodeId 0
-  -- (self), but from the caller's node it is addressed by the assigned id.
-  let toRemote nid ref =
-        let ActorId _ u = someActorId (SomeActorRef ref)
-        in  RemoteRef (ActorId nid u)
-
-  -- Spawn workers on node 2.
+  -- Spawn and register workers on node 2.
   echoRef  <- withRuntime rt2 $ spawnActor echoActor   stopOnDeath ()
   printRef <- withRuntime rt2 $ spawnActor printerActor stopOnDeath ()
+  withRuntime rt2 $ registerActor "echo"    echoRef
+  withRuntime rt2 $ registerActor "printer" printRef
 
-  let remoteEcho  = toRemote node2 echoRef  :: ActorRef String String
-      remotePrint = toRemote node2 printRef :: ActorRef String ()
+  -- Small delay to let NMRegistryUpdate propagate to node 1.
+  threadDelay 100_000
 
   -- 1. Remote cast: fire-and-forget from node 1 to node 2.
   putStrLn "\n[1] remote cast  node 1 -> node 2"
+  Just remotePrint <- withRuntime rt1 $ lookupRemoteActor "printer"
   withRuntime rt1 $ cast' "hello from node 1" remotePrint
   threadDelay 300_000
 
   -- 2. Remote call: request/reply across nodes.
   putStrLn "\n[2] remote call  node 1 <-> node 2"
+  Just remoteEcho' <- withRuntime rt1 $ lookupRemoteActor "echo"
+  let
+    remoteEcho :: ActorRef String String
+    remoteEcho = (unsafeCoerce remoteEcho')
   reply <- withRuntime rt1 $ call' "ping" remoteEcho
   putStrLn $ "    reply: " <> show reply
 
@@ -161,7 +161,9 @@ networkDemo = do
   putStrLn "\n[3] reverse cast  node 2 -> node 1"
   recvVar <- newTVarIO (Nothing :: Maybe String)
   recvRef <- withRuntime rt1 $ spawnActor (recvActorFn recvVar) stopOnDeath ()
-  let remoteRecv = toRemote node1 recvRef :: ActorRef String ()
+  withRuntime rt1 $ registerActor "receiver" recvRef
+  threadDelay 100_000
+  Just remoteRecv <- withRuntime rt2 $ lookupRemoteActor "receiver"
   withRuntime rt2 $ cast' "hello from node 2" remoteRecv
   threadDelay 300_000
   readTVarIO recvVar >>= \v -> putStrLn $ "    received: " <> show v
@@ -184,13 +186,11 @@ networkDemo = do
   let mortalId = someActorId (SomeActorRef mortalRef)
       watchId  = someActorId (SomeActorRef watchRef)
 
-  -- mortalRef's links: on death, send NMDeath to node 1's address.
-  withRuntime rt2 $
-    linkActorTo (RemoteTarget watchId  addr1) mortalRef
+  -- mortalRef's links: on death, send NMDeath to node 1 (by NodeId).
+  withRuntime rt2 $ linkActorTo (RemoteTarget watchId  node1) mortalRef
   -- watchRef's links: declare interest in mortalId so routeRemoteDeath
   -- on node 1 can find this actor when NMDeath arrives.
-  withRuntime rt1 $
-    linkActorTo (RemoteTarget mortalId addr2) watchRef
+  withRuntime rt1 $ linkActorTo (RemoteTarget mortalId node2) watchRef
 
   -- Kill the mortal actor by posting directly to its death queue.
   case mortalRef of

src/Control/Actor/Core.hs

@@ -11,6 +11,7 @@ module Control.Actor.Core
   , liftRuntime
   , notifyOfDeath
   , spawnActor
+  , spawnActorAs
   , linkActorTo
   , linkTo
   , killActor
@@ -20,6 +21,12 @@ module Control.Actor.Core
   , cast
   , call
   , castIn
+  , pass
+  , passWith
+  , continue
+  , maybeContinue
+  , become
+  , lastMessageFrom
   ) where
 
 import Control.Actor.Runtime
@@ -56,6 +63,7 @@ import Control.Monad.Reader
   )
 import Data.Binary (Binary, decode, encode)
 import Data.Map qualified as Map
+import Data.UUID (UUID)
 import Data.UUID.V4 (nextRandom)
 
 newtype ActorM u r = ActorM
@@ -71,6 +79,9 @@ runActorM m rt s = runReaderT (unActorM m) (s, rt)
 state :: ActorM u u
 state = asks (asEnv . fst)
 
+lastMessageFrom :: ActorM u NodeId
+lastMessageFrom = asks (asLatestFrom . fst)
+
 getSelf :: ActorM u SomeActorRef
 getSelf = do
   (as, rt) <- ask
@@ -95,24 +106,28 @@ liftRuntime :: RuntimeM a -> ActorM u a
 liftRuntime = ActorM . withReaderT snd . unRuntimeM
 
 notifyOfDeath :: Runtime -> DeathMessage -> DeathTarget -> IO ()
-notifyOfDeath _  dm (LocalTarget q)           = atomically $ writeTQueue q dm
-notifyOfDeath rt dm (RemoteTarget _ peerAddr) =
-  withRuntime rt $ rtSendRemote rt peerAddr (NMDeath (dmActorId dm) (toRemoteExitReason (dmReason dm)))
+notifyOfDeath _  dm (LocalTarget q)         = atomically $ writeTQueue q dm
+notifyOfDeath rt dm (RemoteTarget _ nodeId) =
+  withRuntime rt $ do
+    maybeAddr <- lookupNode nodeId
+    case maybeAddr of
+      Nothing   -> return ()
+      Just addr -> rtSendRemote rt addr (NMDeath (dmActorId dm) (toRemoteExitReason (dmReason dm)))
 
-spawnActor ::
+spawnActorAs ::
   (Binary m, Binary r) =>
+  UUID ->
   Handler m u r ->
   (DeathMessage -> ActorM u (SupervisorAction u)) ->
   u ->
   RuntimeM (ActorRef m r)
-spawnActor actorFn deathFn initState = do
+spawnActorAs uuid actorFn deathFn initState = do
   rt      <- ask
   mailbox <- liftIO newTQueueIO
   deathQ  <- liftIO newTQueueIO
   links   <- liftIO $ newTVarIO []
-  uuid    <- liftIO nextRandom
   let actorId    = ActorId thisNodeId uuid
-      actorState = ActorState actorId links initState
+      actorState = ActorState actorId links initState thisNodeId
       actorRef   = LocalRef mailbox deathQ actorState
 
   let loop fn as = do
@@ -123,11 +138,11 @@ spawnActor actorFn deathFn initState = do
         case event of
           Left envelope ->
             case envelope of
-              Cast msg -> do
-                ActorResult _ u' mFn <- runActorM (fn msg) rt as
+              (from, Cast msg) -> do
+                ActorResult _ u' mFn <- runActorM (fn msg) rt as {asLatestFrom = from}
                 loop (fromMaybe fn mFn) as {asEnv = u'}
-              Call msg mv -> do
-                ActorResult reply u' mFn <- runActorM (fn msg) rt as
+              (from, Call msg mv) -> do
+                ActorResult reply u' mFn <- runActorM (fn msg) rt as {asLatestFrom = from}
                 putMVar mv reply
                 loop (fromMaybe fn mFn) as {asEnv = u'}
           Right dm -> do
@@ -154,6 +169,16 @@ spawnActor actorFn deathFn initState = do
     modifyTVar (rtActors rt) (Map.insert actorId (tid, SomeActorRef actorRef))
   return actorRef
 
+spawnActor ::
+  (Binary m, Binary r) =>
+  Handler m u r ->
+  (DeathMessage -> ActorM u (SupervisorAction u)) ->
+  u ->
+  RuntimeM (ActorRef m r)
+spawnActor actorFn deathFn initState = do
+  uuid <- liftIO nextRandom
+  spawnActorAs uuid actorFn deathFn initState
+
 linkActorTo :: DeathTarget -> ActorRef m r -> RuntimeM ()
 linkActorTo target (LocalRef {arState}) =
   liftIO $ atomically $ modifyTVar (asLinks arState) (target :)
@@ -175,7 +200,7 @@ stopOnDeath _ = return Stop
 
 cast' :: (Binary msg) => msg -> ActorRef msg reply -> RuntimeM ()
 cast' msg (LocalRef {arMsgQ}) =
-  liftIO $ atomically $ writeTQueue arMsgQ (Cast msg)
+  liftIO $ atomically $ writeTQueue arMsgQ (thisNodeId, Cast msg)
 cast' msg (RemoteRef (ActorId nodeId uuid)) = do
   rt <- ask
   maybeAddr <- lookupNode nodeId
@@ -186,7 +211,7 @@ cast' msg (RemoteRef (ActorId nodeId uuid)) = do
 call' :: (Binary msg, Binary reply) => msg -> ActorRef msg reply -> RuntimeM (Maybe reply)
 call' msg (LocalRef {arMsgQ}) = liftIO $ do
   mv <- newEmptyMVar
-  atomically $ writeTQueue arMsgQ (Call msg mv)
+  atomically $ writeTQueue arMsgQ (thisNodeId, Call msg mv)
   takeMVar mv
 call' msg (RemoteRef (ActorId nodeId uuid)) = do
   rt <- ask
@@ -220,3 +245,19 @@ castIn ms msg ref = do
 
 call :: (Binary msg, Binary reply) => msg -> ActorRef msg reply -> ActorM u (Maybe reply)
 call = (liftRuntime .) . call'
+
+continue :: r -> Actor msg u r
+continue x = (\u -> ActorResult (Just x) u Nothing) <$> state
+
+maybeContinue :: Maybe r -> Actor msg u r
+maybeContinue Nothing = pass
+maybeContinue (Just r) = continue r
+
+pass :: Actor msg u r
+pass = (\u -> ActorResult Nothing u Nothing) <$> state
+
+passWith :: u -> Actor msg u r
+passWith u = return (ActorResult Nothing u Nothing)
+
+become :: Handler msg u r -> Actor msg u r
+become fn = (\u -> ActorResult Nothing u (Just fn)) <$> state

src/Control/Actor/Network.hs

@@ -10,16 +10,17 @@ module Control.Actor.Network
   , routeRemoteDeath
   , validateAndDispatch
   , sysHandlerFn
-  , initRuntime
+  , createTCPTransport
   ) where
 
 import Control.Actor.Core
-  ( Actor, ActorM, ActorResult (..), Handler, cast', liftRuntime, linkActorTo, spawnActor, state, stopOnDeath )
-import Control.Actor.Runtime (Runtime (..), RuntimeM, newRuntime, withRuntime)
+  ( ActorM, ActorResult (..), Handler, cast', liftRuntime, linkActorTo
+  , spawnActor, state, stopOnDeath )
+import Control.Actor.Runtime (Runtime (..), RuntimeM, addrToNodeId, withRuntime)
 import Control.Actor.Supervision (ChildSpec (..), RestartStrategy (..), childWithRef, supervise')
 import Control.Actor.Transport (ConnHandle (..), Transport (..), createTCPTransport)
 import Control.Actor.Types
-import Control.Concurrent (ThreadId, forkIO)
+import Control.Concurrent (forkIO)
 import Control.Concurrent.MVar (newEmptyMVar, putMVar, takeMVar)
 import Control.Concurrent.STM
   ( atomically
@@ -41,7 +42,7 @@ import Control.Monad.Reader (MonadIO (..), MonadReader (..))
 import Data.Binary (decode, decodeOrFail, encode)
 import Data.ByteString.Lazy (ByteString)
 import Data.Map qualified as Map
-import Data.UUID (UUID)
+import Data.Maybe (fromMaybe)
 
 -- Connection actors
 
@@ -152,20 +153,12 @@ getOrCreateConn peer = do
 
 -- Message dispatch
 
-findByUUID :: UUID -> Map.Map ActorId (ThreadId, SomeActorRef) -> Maybe SomeActorRef
-findByUUID uuid actors =
-  case Map.toList (Map.filterWithKey (\(ActorId _ u) _ -> u == uuid) actors) of
-    []            -> Nothing
-    (_, (_, r)):_ -> Just r
-
 routeRemoteDeath :: NodeAddr -> ActorId -> RemoteExitReason -> RuntimeM ()
 routeRemoteDeath senderAddr (ActorId _ uuid) reason = do
-  rt <- ask
+  rt           <- ask
+  mSenderNid   <- addrToNodeId senderAddr
   liftIO $ do
-    localNodeId <- atomically $ do
-      table <- readTVar (rtNodeTable rt)
-      return $ Map.foldrWithKey (\k v acc -> if v == senderAddr then Just k else acc) Nothing table
-    let deadId     = ActorId (case localNodeId of { Just n -> n; Nothing -> 0 }) uuid
+    let deadId     = ActorId (fromMaybe 0 mSenderNid) uuid
         exitReason = case reason of
           RNormal      -> Normal
           RKilled      -> Killed
@@ -177,9 +170,9 @@ routeRemoteDeath senderAddr (ActorId _ uuid) reason = do
         LocalRef {arDeathQ, arState} -> do
           links <- readTVarIO (asLinks arState)
           forM_ links $ \case
-            RemoteTarget (ActorId _ uid) peerAddr
-              | uid == uuid && peerAddr == senderAddr ->
-                atomically $ writeTQueue arDeathQ dm
+            RemoteTarget (ActorId _ uid) nodeId
+              | uid == uuid && Just nodeId == mSenderNid ->
+                  atomically $ writeTQueue arDeathQ dm
             _else -> return ()
         RemoteRef _ -> return ()
 
@@ -198,6 +191,7 @@ validateAndDispatch senderAddr nm = case nm of
 
   NMCast uuid payload -> do
     rt <- ask
+    rid <- remoteNodeId
     liftIO $ do
       actors <- readTVarIO (rtActors rt)
       case findByUUID uuid actors of
@@ -207,13 +201,14 @@ validateAndDispatch senderAddr nm = case nm of
           case decodeOrFail payload of
             Left _            -> return False
             Right (_, _, msg) -> do
-              atomically $ writeTQueue arMsgQ (Cast msg)
+              atomically $ writeTQueue arMsgQ (rid, Cast msg)
               return True
         Just (SomeActorRef (RemoteRef _)) ->
           return False
 
   NMCall uuid corrId returnAddr payload -> do
     rt <- ask
+    rid <- remoteNodeId
     liftIO $ do
       actors <- readTVarIO (rtActors rt)
       case findByUUID uuid actors of
@@ -224,7 +219,7 @@ validateAndDispatch senderAddr nm = case nm of
             Left _            -> return False
             Right (_, _, msg) -> do
               mv <- newEmptyMVar
-              atomically $ writeTQueue arMsgQ (Call msg mv)
+              atomically $ writeTQueue arMsgQ (rid, Call msg mv)
               void $ forkIO $ do
                 reply <- takeMVar mv
                 case reply of
@@ -240,6 +235,9 @@ validateAndDispatch senderAddr nm = case nm of
     routeRemoteDeath senderAddr deadId reason
     return True
 
+  where
+    remoteNodeId = fromMaybe thisNodeId <$> addrToNodeId senderAddr
+
 -- System event handler
 
 sysHandlerFn :: Handler NetworkMessage () ()
@@ -264,18 +262,3 @@ connect suggestedId peer = do
     return assigned
   void $ getOrCreateConn peer
   return nodeId
-
--- Runtime initialization
-
-initRuntime :: NodeAddr -> IO Runtime
-initRuntime myAddr = do
-  (transport, actualAddr) <- createTCPTransport myAddr
-  rt0 <- newRuntime actualAddr transport
-  let rt = rt0 { rtSendRemote = \addr nm -> getOrCreateConn addr >>= cast' nm }
-  withRuntime rt $ void $ spawnActor sysHandlerFn stopOnDeath ()
-  tListen transport $ \ch -> do
-    result <- try @SomeException $ withRuntime rt $ handleNewConn ch
-    case result of
-      Left _   -> chClose ch
-      Right () -> return ()
-  return rt

src/Control/Actor/Registry.hs

@@ -0,0 +1,131 @@
+module Control.Actor.Registry
+  ( registerActor,
+    lookupActor,
+    lookupRemoteActor,
+    registryUUID,
+    registry,
+    registerDeath,
+    createRegistry,
+  )
+where
+
+import Control.Actor.Core (ActorM, ActorResult (..), Handler, call, call', cast', liftRuntime, linkActorTo, pass, spawnActorAs, state, lastMessageFrom, cast, passWith)
+import Control.Actor.Runtime (Runtime (..), RuntimeM, getActorByUUID, withRuntime)
+import Control.Actor.Types (ActorId (..), ActorRef (..), DeathMessage (..), DeathTarget (LocalTarget), RegistryMsg (..), SomeActorRef (..), SupervisorAction (Continue), actorRefId, thisNodeId, findByUUID)
+import Control.Concurrent.STM (readTVarIO)
+import Control.Monad (forM_, when)
+import Control.Monad.IO.Class (MonadIO (liftIO))
+import Control.Monad.Reader (ask)
+import Data.Map qualified as Map
+import Data.UUID (UUID, fromWords)
+import Unsafe.Coerce (unsafeCoerce)
+
+registryUUID :: UUID
+registryUUID = fromWords 0 0 0 1
+
+type RegistryState = Map.Map String ActorId
+
+registryHandlerFn :: Handler RegistryMsg RegistryState (Maybe ActorId)
+registryHandlerFn msg@(RMRegister name uuid) = do
+  u <- state
+  from <- lastMessageFrom
+  when (from == thisNodeId) $ do
+    rt <- liftRuntime ask
+    nodeTable <- liftIO $ readTVarIO (rtNodeTable rt)
+    forM_ (Map.keys nodeTable) $ \nodeId -> do
+      cast msg (RemoteRef (ActorId nodeId registryUUID))
+  passWith (Map.insert name (ActorId from uuid) u)
+registryHandlerFn (RMLookup name) = do
+  u <- state
+  return $ ActorResult (Just (Map.lookup name u)) u Nothing
+registryHandlerFn (RMDeregister name) = do
+  u <- state
+  return $ ActorResult Nothing (Map.delete name u) Nothing
+registryHandlerFn msg@(RMDeath deadUUID) = do
+  u <- state
+  from <- lastMessageFrom
+
+  let (_, kept) = Map.partition (\(ActorId _ uuid) -> uuid == deadUUID) u
+
+  when (from == thisNodeId) $ do
+    rt <- liftRuntime ask
+    nodeTable <- liftIO $ readTVarIO (rtNodeTable rt)
+    forM_ (Map.keys nodeTable) $ \nodeId -> do
+      cast msg (RemoteRef (ActorId nodeId registryUUID))
+
+  passWith kept
+
+registryDeathFn :: DeathMessage -> ActorM RegistryState (SupervisorAction RegistryState)
+registryDeathFn (DeathMessage (ActorId _ deadUUID) _) = do
+  u <- state
+  let (_, kept) = Map.partition (\(ActorId _ uuid) -> uuid == deadUUID) u
+  rt <- liftRuntime ask
+  nodeTable <- liftIO $ readTVarIO (rtNodeTable rt)
+  forM_ (Map.keys nodeTable) $ \nodeId -> do
+    cast (RMDeath deadUUID) (RemoteRef (ActorId nodeId registryUUID))
+
+  return $ Continue kept
+
+registry :: RuntimeM (Maybe (ActorRef RegistryMsg (Maybe ActorId)))
+registry = do
+  unsafeCoerce $ getActorByUUID registryUUID
+
+registerDeath :: ActorId -> RuntimeM ()
+registerDeath (ActorId _ uuid) = do
+  r <- registry
+  mapM_ (cast' (RMDeath uuid)) r
+
+registerActor :: String -> ActorRef msg r -> RuntimeM ()
+registerActor name ref = do
+  rt <- ask
+  let ActorId _ uuid = actorRefId ref
+  actors <- liftIO $ readTVarIO (rtActors rt)
+  case findByUUID registryUUID actors of
+    Just (SomeActorRef regRef) -> do
+      let reg = unsafeCoerce regRef :: ActorRef RegistryMsg (Maybe ActorId)
+      cast' (RMRegister name uuid) reg
+      case reg of
+        LocalRef {arDeathQ} -> linkActorTo (LocalTarget arDeathQ) ref
+        RemoteRef _ -> return ()
+    Nothing -> liftIO $ putStrLn "registerActor: registry not found"
+
+lookupActor :: String -> RuntimeM (Maybe (ActorRef msg r))
+lookupActor name = do
+  rt <- ask
+  actors <- liftIO $ readTVarIO (rtActors rt)
+  case findByUUID registryUUID actors of
+    Nothing -> return Nothing
+    Just (SomeActorRef regRef) -> do
+      result <-
+        call'
+          (RMLookup name)
+          (unsafeCoerce regRef :: ActorRef RegistryMsg (Maybe ActorId))
+      case result of
+        Just (Just (ActorId 0 uuid)) -> do
+          actors' <- liftIO $ readTVarIO (rtActors rt)
+          return $ fmap (\(SomeActorRef r) -> unsafeCoerce r) (findByUUID uuid actors')
+        Just (Just aid) -> return $ Just (RemoteRef aid)
+        _else -> return Nothing
+
+lookupRemoteActor :: String -> RuntimeM (Maybe (ActorRef msg r))
+lookupRemoteActor name = do
+  rt <- ask
+  table <- liftIO $ readTVarIO (rtNodeTable rt)
+  go (Map.keys table)
+  where
+    go [] = return Nothing
+    go (peerNodeId : rest) = do
+      let remoteReg =
+            RemoteRef (ActorId peerNodeId registryUUID) ::
+              ActorRef RegistryMsg (Maybe ActorId)
+      result <- call' (RMLookup name) remoteReg
+      case result of
+        Just (Just (ActorId 0 uuid)) ->
+          return $ Just (RemoteRef (ActorId peerNodeId uuid))
+        Just (Just aid) ->
+          return $ Just (RemoteRef aid)
+        _else -> go rest
+
+createRegistry :: RuntimeM (ActorRef RegistryMsg (Maybe ActorId))
+createRegistry =
+  spawnActorAs registryUUID registryHandlerFn registryDeathFn Map.empty

src/Control/Actor/Runtime.hs

@@ -6,6 +6,9 @@ module Control.Actor.Runtime
   , newRuntime
   , withRuntime
   , lookupNode
+  , addrToNodeId
+  , getActorRef
+  , getActorByUUID
   ) where
 
 import Control.Actor.Transport (Transport)
@@ -13,11 +16,13 @@ import Control.Actor.Types
 import Control.Concurrent (ThreadId)
 import Control.Concurrent.MVar (MVar)
 import Control.Concurrent.STM
-  ( TMVar, TVar, atomically, newTVarIO, readTVar )
+  ( TMVar, TVar, atomically, newTVarIO, readTVar, readTVarIO )
 import Control.Monad.Reader
-  ( MonadIO (..), MonadReader (..), ReaderT (..), runReaderT )
+  ( MonadIO (..), MonadReader (..), ReaderT (..), runReaderT, asks )
 import Data.ByteString.Lazy (ByteString)
+import Data.Foldable (foldl')
 import Data.Map qualified as Map
+import Data.UUID (UUID)
 
 data Runtime = Runtime
   { rtNodeId       :: NodeAddr
@@ -68,3 +73,30 @@ lookupNode nodeId = do
   liftIO $ atomically $ do
     table <- readTVar (rtNodeTable rt)
     return $ Map.lookup nodeId table
+
+addrToNodeId :: NodeAddr -> RuntimeM (Maybe NodeId)
+addrToNodeId addr = do
+  rt <- ask
+  liftIO $ atomically $ do
+    table <- readTVar (rtNodeTable rt)
+    return $ Map.foldrWithKey (\k v acc -> if v == addr then Just k else acc) Nothing table
+
+getActorRef :: ActorId -> RuntimeM (Maybe SomeActorRef)
+getActorRef aid = do
+  actVar <- asks rtActors
+  actors <- liftIO $ readTVarIO actVar
+  return $ snd <$> Map.lookup aid actors
+
+firstByKey' :: Ord k => (k -> Bool) -> Map.Map k v -> Maybe v
+firstByKey' p = snd . foldl' step (False, Nothing) . Map.toAscList
+  where
+    step (True, mv) _ = (True, mv)
+    step (False, _) (k,v)
+      | p k       = (True, Just v)
+      | otherwise = (False, Nothing)
+
+getActorByUUID :: UUID -> RuntimeM (Maybe SomeActorRef)
+getActorByUUID uuid = do
+  actVar <- asks rtActors
+  actors <- liftIO $ readTVarIO actVar
+  return $ snd <$> firstByKey' (\(ActorId _ x) -> x == uuid) actors

src/Control/Actor/Supervision.hs

@@ -16,7 +16,7 @@ module Control.Actor.Supervision
   , killSlot
   ) where
 
-import Control.Actor.Core (Actor, ActorM, Handler, liftRuntime, linkActorTo, spawnActor)
+import Control.Actor.Core (ActorM, Handler, liftRuntime, linkActorTo, spawnActor)
 import Control.Actor.Runtime (Runtime (..), RuntimeM, withRuntime)
 import Control.Actor.Types
 import Data.Binary (Binary)

src/Control/Actor/Types.hs

@@ -16,9 +16,12 @@ module Control.Actor.Types
   , ActorRef (..)
   , SomeActorRef (..)
   , someActorId
+  , actorRefId
   , SupervisorAction (..)
   , CorrelationId
   , Envelope (..)
+  , RegistryMsg (..)
+  , findByUUID
   ) where
 
 import Control.Concurrent.MVar (MVar)
@@ -28,6 +31,8 @@ import Data.Binary (Binary)
 import Data.ByteString.Lazy (ByteString)
 import Data.UUID (UUID)
 import GHC.Generics (Generic)
+import Data.Map qualified as Map
+import Control.Concurrent (ThreadId)
 
 data NodeAddr = NodeAddr
   { nodeHost :: String
@@ -59,7 +64,7 @@ data DeathMessage = DeathMessage
 
 data DeathTarget
   = LocalTarget (TQueue DeathMessage)
-  | RemoteTarget ActorId NodeAddr
+  | RemoteTarget ActorId NodeId
 
 data RemoteExitReason
   = RNormal
@@ -88,6 +93,7 @@ data ActorState u = ActorState
   { asId    :: ActorId
   , asLinks :: TVar [DeathTarget]
   , asEnv   :: u
+  , asLatestFrom :: NodeId
   }
 
 type CorrelationId = Integer
@@ -98,7 +104,7 @@ data Envelope msg reply
 
 data ActorRef msg reply
   = forall u. LocalRef
-      { arMsgQ   :: TQueue (Envelope msg reply)
+      { arMsgQ   :: TQueue (NodeId, Envelope msg reply)
       , arDeathQ :: TQueue DeathMessage
       , arState  :: ActorState u
       }
@@ -110,6 +116,25 @@ someActorId :: SomeActorRef -> ActorId
 someActorId (SomeActorRef (LocalRef {arState})) = asId arState
 someActorId (SomeActorRef (RemoteRef aid))      = aid
 
+actorRefId :: ActorRef msg r -> ActorId
+actorRefId (LocalRef {arState}) = asId arState
+actorRefId (RemoteRef aid)      = aid
+
 data SupervisorAction u
   = Stop
   | Continue u
+
+data RegistryMsg
+  = RMRegister   String UUID
+  | RMLookup     String
+  | RMDeregister String
+  | RMDeath      UUID
+  deriving (Generic)
+
+instance Binary RegistryMsg
+
+findByUUID :: UUID -> Map.Map ActorId (ThreadId, SomeActorRef) -> Maybe SomeActorRef
+findByUUID uuid actors =
+  case Map.toList (Map.filterWithKey (\(ActorId _ u) _ -> u == uuid) actors) of
+    []            -> Nothing
+    (_, (_, r)):_ -> Just r