Refactoring connection pool

- replace RWMutex with Mutex
- conns now contains `map[int32][]*node`
- add index field to node struct
- add usedAt field to node struct
- `New` don't store current connection twice
- writes `used_at` of connection into the log
- we check that conn is alive and, that connection used not a long time ago, otherwise, close it
- `getConnection` reset current connection and index on errors
-  `IsAlive` now is a method of `Pool`
-  `IsAlive` creates context with timeout for every health check call of node

pool.go

@@ -14,6 +14,7 @@ import (
 	"github.com/nspcc-dev/neofs-api/service"
 	"github.com/nspcc-dev/neofs-api/state"
 	"github.com/spf13/viper"
+	"go.uber.org/atomic"
 	"go.uber.org/zap"
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/connectivity"
@@ -22,23 +23,29 @@ import (
 
 type (
 	node struct {
+		index   int32
 		address string
 		weight  uint32
+		usedAt  time.Time
 		conn    *grpc.ClientConn
 	}
 
 	Pool struct {
 		log *zap.Logger
 
+		ttl time.Duration
+
 		connectTimeout time.Duration
+		requestTimeout time.Duration
 		opts           keepalive.ClientParameters
 
-		cur *grpc.ClientConn
+		currentIdx  *atomic.Int32
+		currentConn *grpc.ClientConn
 
-		*sync.RWMutex
+		*sync.Mutex
 		nodes []*node
 		keys  []uint32
-		conns map[uint32][]*grpc.ClientConn
+		conns map[uint32][]*node
 	}
 )
 
@@ -50,19 +57,25 @@ var (
 func newPool(ctx context.Context, l *zap.Logger, v *viper.Viper) *Pool {
 	p := &Pool{
 		log:   l,
-		RWMutex: new(sync.RWMutex),
+		Mutex: new(sync.Mutex),
 		keys:  make([]uint32, 0),
 		nodes: make([]*node, 0),
-		conns:   make(map[uint32][]*grpc.ClientConn),
+		conns: make(map[uint32][]*node),
+
+		ttl: defaultTTL,
+
+		currentIdx: atomic.NewInt32(-1),
 
 		// fill with defaults:
-		connectTimeout: time.Second * 15,
+		requestTimeout: defaultRequestTimeout,
+		connectTimeout: defaultConnectTimeout,
 		opts: keepalive.ClientParameters{
-			Time:                time.Second * 10,
+			Time:                defaultKeepaliveTime,
-			Timeout:             time.Minute * 5,
+			Timeout:             defaultKeepaliveTimeout,
 			PermitWithoutStream: true,
 		},
 	}
+
 	buf := make([]byte, 8)
 	if _, err := crand.Read(buf); err != nil {
 		l.Panic("could not read seed", zap.Error(err))
@@ -72,6 +85,10 @@ func newPool(ctx context.Context, l *zap.Logger, v *viper.Viper) *Pool {
 	rand.Seed(int64(seed))
 	l.Info("used random seed", zap.Uint64("seed", seed))
 
+	if val := v.GetDuration("conn_ttl"); val > 0 {
+		p.ttl = val
+	}
+
 	if val := v.GetDuration("connect_timeout"); val > 0 {
 		p.connectTimeout = val
 	}
@@ -99,6 +116,7 @@ func newPool(ctx context.Context, l *zap.Logger, v *viper.Viper) *Pool {
 		}
 
 		p.nodes = append(p.nodes, &node{
+			index:   int32(i),
 			address: address,
 			weight:  uint32(weight * 100),
 		})
@@ -110,13 +128,10 @@ func newPool(ctx context.Context, l *zap.Logger, v *viper.Viper) *Pool {
 
 	p.reBalance(ctx)
 
-	cur, err := p.getConnection(ctx)
+	if _, err := p.getConnection(ctx); err != nil {
-	if err != nil {
 		l.Panic("could get connection", zap.Error(err))
 	}
 
-	p.cur = cur
-
 	return p
 }
 
@@ -173,21 +188,25 @@ func (p *Pool) reBalance(ctx context.Context) {
 			}
 
 			p.nodes[i].conn = conn
+			p.nodes[i].usedAt = time.Now()
 			p.log.Info("connected to node", zap.String("address", p.nodes[i].address))
 		}
 
 		for j := range p.conns[weight] {
-			if p.conns[weight][j] == conn {
+			if p.conns[weight][j] != nil && p.conns[weight][j].conn == conn {
 				idx = j
 				exists = true
 				break
 			}
 		}
 
-		// if something wrong with connection (bad state or unhealthy), try to close it and remove
+		usedAt := time.Since(p.nodes[i].usedAt)
-		if err = isAlive(ctx, p.log, conn); err != nil {
+
+		// if something wrong with connection (bad state, unhealthy or not used a long time), try to close it and remove
+		if err = p.isAlive(ctx, conn); err != nil || usedAt > p.ttl {
 			p.log.Warn("connection not alive",
 				zap.String("address", p.nodes[i].address),
+				zap.Duration("used_at", usedAt),
 				zap.Error(err))
 
 			if exists {
@@ -198,6 +217,7 @@ func (p *Pool) reBalance(ctx context.Context) {
 			if err = conn.Close(); err != nil {
 				p.log.Warn("could not close bad connection",
 					zap.String("address", p.nodes[i].address),
+					zap.Duration("used_at", usedAt),
 					zap.Error(err))
 			}
 
@@ -209,8 +229,12 @@ func (p *Pool) reBalance(ctx context.Context) {
 
 		keys[weight] = struct{}{}
 
+		p.log.Info("connection alive",
+			zap.String("address", p.nodes[i].address),
+			zap.Duration("used_at", usedAt))
+
 		if !exists {
-			p.conns[weight] = append(p.conns[weight], conn)
+			p.conns[weight] = append(p.conns[weight], p.nodes[i])
 		}
 	}
 
@@ -225,11 +249,15 @@ func (p *Pool) reBalance(ctx context.Context) {
 }
 
 func (p *Pool) getConnection(ctx context.Context) (*grpc.ClientConn, error) {
-	p.RLock()
+	p.Lock()
-	defer p.RUnlock()
+	defer p.Unlock()
 
-	if err := isAlive(ctx, p.log, p.cur); err == nil {
+	if err := p.isAlive(ctx, p.currentConn); err == nil {
-		return p.cur, nil
+		if id := p.currentIdx.Load(); id != -1 && p.nodes[id] != nil {
+			p.nodes[id].usedAt = time.Now()
+		}
+
+		return p.currentConn, nil
 	}
 
 	for _, w := range p.keys {
@@ -237,19 +265,26 @@ func (p *Pool) getConnection(ctx context.Context) (*grpc.ClientConn, error) {
 		case 0:
 			continue
 		case 1:
-			p.cur = p.conns[w][0]
+			p.currentConn = p.conns[w][0].conn
-			return p.cur, nil
+			p.conns[w][0].usedAt = time.Now()
+			p.currentIdx.Store(p.conns[w][0].index)
+			return p.currentConn, nil
 		default: // > 1
 			i := rand.Intn(ln)
-			p.cur = p.conns[w][i]
+			p.currentConn = p.conns[w][i].conn
-			return p.cur, nil
+			p.conns[w][i].usedAt = time.Now()
+			p.currentIdx.Store(p.conns[w][i].index)
+			return p.currentConn, nil
 		}
 	}
 
+	p.currentConn = nil
+	p.currentIdx.Store(-1)
+
 	return nil, errNoHealthyConnections
 }
 
-func isAlive(ctx context.Context, log *zap.Logger, cur *grpc.ClientConn) error {
+func (p *Pool) isAlive(ctx context.Context, cur *grpc.ClientConn) error {
 	if cur == nil {
 		return errEmptyConnection
 	}
@@ -259,9 +294,12 @@ func isAlive(ctx context.Context, log *zap.Logger, cur *grpc.ClientConn) error {
 		req := new(state.HealthRequest)
 		req.SetTTL(service.NonForwardingTTL)
 
+		ctx, cancel := context.WithTimeout(ctx, p.requestTimeout)
+		defer cancel()
+
 		res, err := state.NewStatusClient(cur).HealthCheck(ctx, req)
 		if err != nil {
-			log.Warn("could not fetch health-check", zap.Error(err))
+			p.log.Warn("could not fetch health-check", zap.Error(err))
 
 			return err
 		} else if !res.Healthy {