[#1170] pkg/morph: Add worker pool

Add worker pool to the listener to prevent blocking. It is used only for
notary notifications and new block events handling since it uses RPC
calls. That may lead to the deadlock state: neo-go cannot send RPC until
notification channel is read but notification channel cannot be read since
neo-go client cannot send RPC.

Signed-off-by: Pavel Karpy <carpawell@nspcc.ru>

pkg/morph/event/listener.go

@@ -11,6 +11,7 @@ import (
 	"github.com/nspcc-dev/neo-go/pkg/util"
 	"github.com/nspcc-dev/neofs-node/pkg/morph/client"
 	"github.com/nspcc-dev/neofs-node/pkg/morph/subscriber"
+	"github.com/panjf2000/ants/v2"
 	"go.uber.org/zap"
 )
 
@@ -85,6 +86,8 @@ type ListenerParams struct {
 	Logger *zap.Logger
 
 	Subscriber subscriber.Subscriber
+
+	WorkerPoolCapacity int
 }
 
 type listener struct {
@@ -108,6 +111,8 @@ type listener struct {
 	subscriber subscriber.Subscriber
 
 	blockHandlers []BlockHandler
+
+	pool *ants.Pool
 }
 
 const newListenerFailMsg = "could not instantiate Listener"
@@ -258,7 +263,12 @@ loop:
 				continue loop
 			}
 
-			l.parseAndHandleNotary(notaryEvent)
+			if err = l.pool.Submit(func() {
+				l.parseAndHandleNotary(notaryEvent)
+			}); err != nil {
+				l.log.Warn("listener worker pool drained",
+					zap.Int("capacity", l.pool.Cap()))
+			}
 		case b, ok := <-blockChan:
 			if !ok {
 				l.log.Warn("stop event listener by block channel")
@@ -272,8 +282,13 @@ loop:
 				continue loop
 			}
 
-			for i := range l.blockHandlers {
-				l.blockHandlers[i](b)
+			if err = l.pool.Submit(func() {
+				for i := range l.blockHandlers {
+					l.blockHandlers[i](b)
+				}
+			}); err != nil {
+				l.log.Warn("listener worker pool drained",
+					zap.Int("capacity", l.pool.Cap()))
 			}
 		}
 	}
@@ -586,6 +601,11 @@ func (l *listener) RegisterBlockHandler(handler BlockHandler) {
 
 // NewListener create the notification event listener instance and returns Listener interface.
 func NewListener(p ListenerParams) (Listener, error) {
+	// defaultPoolCap is a default worker
+	// pool capacity if it was not specified
+	// via params
+	const defaultPoolCap = 10
+
 	switch {
 	case p.Logger == nil:
 		return nil, fmt.Errorf("%s: %w", newListenerFailMsg, errNilLogger)
@@ -593,10 +613,21 @@ func NewListener(p ListenerParams) (Listener, error) {
 		return nil, fmt.Errorf("%s: %w", newListenerFailMsg, errNilSubscriber)
 	}
 
+	poolCap := p.WorkerPoolCapacity
+	if poolCap == 0 {
+		poolCap = defaultPoolCap
+	}
+
+	pool, err := ants.NewPool(poolCap, ants.WithNonblocking(true))
+	if err != nil {
+		return nil, fmt.Errorf("could not init worker pool: %w", err)
+	}
+
 	return &listener{
 		notificationParsers:  make(map[scriptHashWithType]NotificationParser),
 		notificationHandlers: make(map[scriptHashWithType][]Handler),
 		log:                  p.Logger,
 		subscriber:           p.Subscriber,
+		pool:                 pool,
 	}, nil
 }