[NOD-1404] Remove most of the notification manager to fix a deadlock (#935)

* [NOD-1404] Remove most of the notification manager to fix a deadlock.

* [NOD-1404] Rename a couple of fields.

app/rpc/rpc.go

@@ -40,16 +40,12 @@ func (m *Manager) routerInitializer(router *router.Router, netConnection *netada
 	if err != nil {
 		panic(err)
 	}
-	spawn("routerInitializer-handleIncomingMessages", func() {
-		err := m.handleIncomingMessages(router, incomingRoute)
-		m.handleError(err, netConnection)
-	})
+	m.context.NotificationManager.AddListener(router)
 
-	notificationListener := m.context.NotificationManager.AddListener(router)
-	spawn("routerInitializer-handleOutgoingNotifications", func() {
+	spawn("routerInitializer-handleIncomingMessages", func() {
 		defer m.context.NotificationManager.RemoveListener(router)
 
-		err := m.handleOutgoingNotifications(notificationListener)
+		err := m.handleIncomingMessages(router, incomingRoute)
 		m.handleError(err, netConnection)
 	})
 }
@@ -76,15 +72,6 @@ func (m *Manager) handleIncomingMessages(router *router.Router, incomingRoute *r
 	}
 }
 
-func (m *Manager) handleOutgoingNotifications(notificationListener *rpccontext.NotificationListener) error {
-	for {
-		err := notificationListener.ProcessNextNotification()
-		if err != nil {
-			return err
-		}
-	}
-}
-
 func (m *Manager) handleError(err error, netConnection *netadapter.NetConnection) {
 	if errors.Is(err, router.ErrTimeout) {
 		log.Warnf("Got timeout from %s. Disconnecting...", netConnection)

app/rpc/rpccontext/notificationmanager.go

@@ -2,7 +2,7 @@ package rpccontext
 
 import (
 	"github.com/kaspanet/kaspad/app/appmessage"
-	"github.com/kaspanet/kaspad/infrastructure/network/netadapter/router"
+	routerpkg "github.com/kaspanet/kaspad/infrastructure/network/netadapter/router"
 	"github.com/pkg/errors"
 	"sync"
 )
@@ -10,58 +10,41 @@ import (
 // NotificationManager manages notifications for the RPC
 type NotificationManager struct {
 	sync.RWMutex
-	listeners map[*router.Router]*NotificationListener
+	listeners map[*routerpkg.Router]*NotificationListener
 }
 
-// OnBlockAddedListener is a listener function for when a block is added to the DAG
-type OnBlockAddedListener func(notification *appmessage.BlockAddedNotificationMessage) error
-
-// OnChainChangedListener is a listener function for when the DAG's selected parent chain changes
-type OnChainChangedListener func(notification *appmessage.ChainChangedNotificationMessage) error
-
 // NotificationListener represents a registered RPC notification listener
 type NotificationListener struct {
-	onBlockAddedListener           OnBlockAddedListener
-	onBlockAddedNotificationChan   chan *appmessage.BlockAddedNotificationMessage
-	onChainChangedListener         OnChainChangedListener
-	onChainChangedNotificationChan chan *appmessage.ChainChangedNotificationMessage
-
-	closeChan chan struct{}
+	propagateBlockAddedNotifications   bool
+	propagateChainChangedNotifications bool
 }
 
 // NewNotificationManager creates a new NotificationManager
 func NewNotificationManager() *NotificationManager {
 	return &NotificationManager{
-		listeners: make(map[*router.Router]*NotificationListener),
+		listeners: make(map[*routerpkg.Router]*NotificationListener),
 	}
 }
 
 // AddListener registers a listener with the given router
-func (nm *NotificationManager) AddListener(router *router.Router) *NotificationListener {
+func (nm *NotificationManager) AddListener(router *routerpkg.Router) {
 	nm.Lock()
 	defer nm.Unlock()
 
 	listener := newNotificationListener()
 	nm.listeners[router] = listener
-	return listener
 }
 
 // RemoveListener unregisters the given router
-func (nm *NotificationManager) RemoveListener(router *router.Router) {
+func (nm *NotificationManager) RemoveListener(router *routerpkg.Router) {
 	nm.Lock()
 	defer nm.Unlock()
 
-	listener, ok := nm.listeners[router]
-	if !ok {
-		return
-	}
-	listener.close()
-
 	delete(nm.listeners, router)
 }
 
 // Listener retrieves the listener registered with the given router
-func (nm *NotificationManager) Listener(router *router.Router) (*NotificationListener, error) {
+func (nm *NotificationManager) Listener(router *routerpkg.Router) (*NotificationListener, error) {
 	nm.RLock()
 	defer nm.RUnlock()
 
@@ -73,67 +56,52 @@ func (nm *NotificationManager) Listener(router *router.Router) (*NotificationLis
 }
 
 // NotifyBlockAdded notifies the notification manager that a block has been added to the DAG
-func (nm *NotificationManager) NotifyBlockAdded(notification *appmessage.BlockAddedNotificationMessage) {
+func (nm *NotificationManager) NotifyBlockAdded(notification *appmessage.BlockAddedNotificationMessage) error {
 	nm.RLock()
 	defer nm.RUnlock()
 
-	for _, listener := range nm.listeners {
-		if listener.onBlockAddedListener != nil {
-			select {
-			case listener.onBlockAddedNotificationChan <- notification:
-			case <-listener.closeChan:
-				continue
+	for router, listener := range nm.listeners {
+		if listener.propagateBlockAddedNotifications {
+			err := router.OutgoingRoute().Enqueue(notification)
+			if err != nil {
+				return err
 			}
 		}
 	}
+	return nil
 }
 
 // NotifyChainChanged notifies the notification manager that the DAG's selected parent chain has changed
-func (nm *NotificationManager) NotifyChainChanged(message *appmessage.ChainChangedNotificationMessage) {
+func (nm *NotificationManager) NotifyChainChanged(notification *appmessage.ChainChangedNotificationMessage) error {
 	nm.RLock()
 	defer nm.RUnlock()
 
-	for _, listener := range nm.listeners {
-		if listener.onChainChangedListener != nil {
-			select {
-			case listener.onChainChangedNotificationChan <- message:
-			case <-listener.closeChan:
-				continue
+	for router, listener := range nm.listeners {
+		if listener.propagateChainChangedNotifications {
+			err := router.OutgoingRoute().Enqueue(notification)
+			if err != nil {
+				return err
 			}
 		}
 	}
+	return nil
 }
 
 func newNotificationListener() *NotificationListener {
 	return &NotificationListener{
-		onBlockAddedNotificationChan:   make(chan *appmessage.BlockAddedNotificationMessage),
-		onChainChangedNotificationChan: make(chan *appmessage.ChainChangedNotificationMessage),
-		closeChan:                      make(chan struct{}, 1),
+		propagateBlockAddedNotifications:   false,
+		propagateChainChangedNotifications: false,
 	}
 }
 
-// SetOnBlockAddedListener sets the onBlockAddedListener handler for this listener
-func (nl *NotificationListener) SetOnBlockAddedListener(onBlockAddedListener OnBlockAddedListener) {
-	nl.onBlockAddedListener = onBlockAddedListener
+// PropagateBlockAddedNotifications instructs the listener to send block added notifications
+// to the remote listener
+func (nl *NotificationListener) PropagateBlockAddedNotifications() {
+	nl.propagateBlockAddedNotifications = true
 }
 
-// SetOnChainChangedListener sets the onChainChangedListener handler for this listener
-func (nl *NotificationListener) SetOnChainChangedListener(onChainChangedListener OnChainChangedListener) {
-	nl.onChainChangedListener = onChainChangedListener
-}
-
-// ProcessNextNotification waits until a notification arrives and processes it
-func (nl *NotificationListener) ProcessNextNotification() error {
-	select {
-	case block := <-nl.onBlockAddedNotificationChan:
-		return nl.onBlockAddedListener(block)
-	case notification := <-nl.onChainChangedNotificationChan:
-		return nl.onChainChangedListener(notification)
-	case <-nl.closeChan:
-		return nil
-	}
-}
-
-func (nl *NotificationListener) close() {
-	nl.closeChan <- struct{}{}
+// PropagateChainChangedNotifications instructs the listener to send chain changed notifications
+// to the remote listener
+func (nl *NotificationListener) PropagateChainChangedNotifications() {
+	nl.propagateChainChangedNotifications = true
 }

app/rpc/rpchandlers/notify_block_added.go

@@ -12,9 +12,7 @@ func HandleNotifyBlockAdded(context *rpccontext.Context, router *router.Router,
 	if err != nil {
 		return nil, err
 	}
-	listener.SetOnBlockAddedListener(func(notification *appmessage.BlockAddedNotificationMessage) error {
-		return router.OutgoingRoute().Enqueue(notification)
-	})
+	listener.PropagateBlockAddedNotifications()
 
 	response := appmessage.NewNotifyBlockAddedResponseMessage()
 	return response, nil

app/rpc/rpchandlers/notify_chain_changed.go

@@ -18,9 +18,7 @@ func HandleNotifyChainChanged(context *rpccontext.Context, router *router.Router
 	if err != nil {
 		return nil, err
 	}
-	listener.SetOnChainChangedListener(func(message *appmessage.ChainChangedNotificationMessage) error {
-		return router.OutgoingRoute().Enqueue(message)
-	})
+	listener.PropagateChainChangedNotifications()
 
 	response := appmessage.NewNotifyChainChangedResponseMessage()
 	return response, nil