[#195] morph: use blocking unlimited pool for notifications

With non-blocking pool restricted by 10 in capacity, the probability of
dropping events is unexpectedly big. Notifications are an essential part of the FrostFS,
we should not drop anything, especially new epochs.
```
Mar 31 07:07:03 vedi neofs-ir[19164]: 2023-03-31T07:07:03.901Z        debug        subscriber/subscriber.go:154        new notification event from sidechain        {"name": "NewEpoch"}
Mar 31 07:07:03 vedi neofs-ir[19164]: 2023-03-31T07:07:03.901Z        warn        event/listener.go:248        listener worker pool drained        {"chain": "morph", "capacity": 10}
```

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

cmd/frostfs-node/morph.go

@@ -181,14 +181,6 @@ func waitNotaryDeposit(ctx context.Context, c *cfg, tx util.Uint256) error {
 }
 
 func listenMorphNotifications(ctx context.Context, c *cfg) {
-	// listenerPoolCap is a capacity of a
-	// worker pool inside the listener. It
-	// is used to prevent blocking in neo-go:
-	// the client cannot make RPC requests if
-	// the notification channel is not being
-	// read by another goroutine.
-	const listenerPoolCap = 10
-
 	var (
 		err  error
 		subs subscriber.Subscriber
@@ -208,9 +200,8 @@ func listenMorphNotifications(ctx context.Context, c *cfg) {
 	fatalOnErr(err)
 
 	lis, err := event.NewListener(event.ListenerParams{
-		Logger:             c.log,
+		Logger:     c.log,
-		Subscriber:         subs,
+		Subscriber: subs,
-		WorkerPoolCapacity: listenerPoolCap,
 	})
 	fatalOnErr(err)
 

pkg/innerring/innerring.go

@@ -409,14 +409,6 @@ func New(ctx context.Context, log *logger.Logger, cfg *viper.Viper, errChan chan
 }
 
 func createListener(ctx context.Context, cli *client.Client, p *chainParams) (event.Listener, error) {
-	// listenerPoolCap is a capacity of a
-	// worker pool inside the listener. It
-	// is used to prevent blocking in neo-go:
-	// the client cannot make RPC requests if
-	// the notification channel is not being
-	// read by another goroutine.
-	const listenerPoolCap = 10
-
 	var (
 		sub subscriber.Subscriber
 		err error
@@ -432,9 +424,8 @@ func createListener(ctx context.Context, cli *client.Client, p *chainParams) (ev
 	}
 
 	listener, err := event.NewListener(event.ListenerParams{
-		Logger:             &logger.Logger{Logger: p.log.With(zap.String("chain", p.name))},
+		Logger:     &logger.Logger{Logger: p.log.With(zap.String("chain", p.name))},
-		Subscriber:         sub,
+		Subscriber: sub,
-		WorkerPoolCapacity: listenerPoolCap,
 	})
 	if err != nil {
 		return nil, err

pkg/morph/event/listener.go

@@ -600,11 +600,6 @@ 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)
@@ -612,12 +607,9 @@ func NewListener(p ListenerParams) (Listener, error) {
 		return nil, fmt.Errorf("%s: %w", newListenerFailMsg, errNilSubscriber)
 	}
 
-	poolCap := p.WorkerPoolCapacity
+	// The pool here must be blocking, otherwise notifications could be dropped.
-	if poolCap == 0 {
+	// The default capacity is 0, which means "infinite".
-		poolCap = defaultPoolCap
+	pool, err := ants.NewPool(p.WorkerPoolCapacity)
-	}
-
-	pool, err := ants.NewPool(poolCap, ants.WithNonblocking(true))
 	if err != nil {
 		return nil, fmt.Errorf("could not init worker pool: %w", err)
 	}