Don't panic if cluster state is nil.

cluster.go

@@ -14,6 +14,7 @@ import (
 )
 
 var errClusterNoNodes = internal.RedisError("redis: cluster has no nodes")
+var errNilClusterState = internal.RedisError("redis: cannot load cluster slots")
 
 // ClusterOptions are used to configure a cluster client and should be
 // passed to NewClusterClient.
@@ -355,7 +356,14 @@ func NewClusterClient(opt *ClusterOptions) *ClusterClient {
 		_, _ = c.nodes.Get(addr)
 	}
 
-	c.reloadSlots()
+	// Preload cluster slots.
+	for i := 0; i < 10; i++ {
+		state, err := c.reloadSlots()
+		if err == nil {
+			c._state.Store(state)
+			break
+		}
+	}
 
 	if opt.IdleCheckFrequency > 0 {
 		go c.reaper(opt.IdleCheckFrequency)
@@ -366,11 +374,12 @@ func NewClusterClient(opt *ClusterOptions) *ClusterClient {
 
 func (c *ClusterClient) state() *clusterState {
 	v := c._state.Load()
-	if v == nil {
+	if v != nil {
-		return nil
-	}
 		return v.(*clusterState)
 	}
+	c.lazyReloadSlots()
+	return nil
+}
 
 func (c *ClusterClient) cmdSlotAndNode(state *clusterState, cmd Cmder) (int, *clusterNode, error) {
 	if state == nil {
@@ -397,10 +406,12 @@ func (c *ClusterClient) cmdSlotAndNode(state *clusterState, cmd Cmder) (int, *cl
 }
 
 func (c *ClusterClient) Watch(fn func(*Tx) error, keys ...string) error {
+	state := c.state()
+
 	var node *clusterNode
 	var err error
-	if len(keys) > 0 {
+	if state != nil && len(keys) > 0 {
-		node, err = c.state().slotMasterNode(hashtag.Slot(keys[0]))
+		node, err = state.slotMasterNode(hashtag.Slot(keys[0]))
 	} else {
 		node, err = c.nodes.Random()
 	}
@@ -463,8 +474,9 @@ func (c *ClusterClient) Process(cmd Cmder) error {
 		var addr string
 		moved, ask, addr = internal.IsMovedError(err)
 		if moved || ask {
-			if slot >= 0 {
+			state := c.state()
-				master, _ := c.state().slotMasterNode(slot)
+			if state != nil && slot >= 0 {
+				master, _ := state.slotMasterNode(slot)
 				if moved && (master == nil || master.Client.getAddr() != addr) {
 					c.lazyReloadSlots()
 				}
@@ -523,7 +535,7 @@ func (c *ClusterClient) ForEachNode(fn func(client *Client) error) error {
 func (c *ClusterClient) ForEachMaster(fn func(client *Client) error) error {
 	state := c.state()
 	if state == nil {
-		return nil
+		return errNilClusterState
 	}
 
 	var wg sync.WaitGroup
@@ -564,12 +576,13 @@ func (c *ClusterClient) ForEachMaster(fn func(client *Client) error) error {
 
 // PoolStats returns accumulated connection pool stats.
 func (c *ClusterClient) PoolStats() *PoolStats {
+	var acc PoolStats
+
 	nodes, err := c.nodes.All()
 	if err != nil {
-		return nil
+		return &acc
 	}
 
-	var acc PoolStats
 	for _, node := range nodes {
 		s := node.Client.connPool.Stats()
 		acc.Requests += s.Requests
@@ -585,37 +598,46 @@ func (c *ClusterClient) lazyReloadSlots() {
 	if !atomic.CompareAndSwapUint32(&c.reloading, 0, 1) {
 		return
 	}
+
 	go func() {
-		c.reloadSlots()
+		for i := 0; i < 1000; i++ {
+			state, err := c.reloadSlots()
+			if err == pool.ErrClosed {
+				break
+			}
+			if err == nil {
+				c._state.Store(state)
+				break
+			}
+			time.Sleep(time.Millisecond)
+		}
+
+		time.Sleep(3 * time.Second)
 		atomic.StoreUint32(&c.reloading, 0)
 	}()
 }
 
-func (c *ClusterClient) reloadSlots() {
+func (c *ClusterClient) reloadSlots() (*clusterState, error) {
-	for i := 0; i < 10; i++ {
 	node, err := c.nodes.Random()
 	if err != nil {
-			return
+		return nil, err
 	}
 
+	// TODO: fix race
 	if c.cmds == nil {
 		cmds, err := node.Client.Command().Result()
-			if err == nil {
+		if err != nil {
-				c.cmds = cmds
+			return nil, err
 		}
+		c.cmds = cmds
 	}
 
 	slots, err := node.Client.ClusterSlots().Result()
 	if err != nil {
-			continue
+		return nil, err
 	}
 
-		state, err := newClusterState(c.nodes, slots)
+	return newClusterState(c.nodes, slots)
-		if err != nil {
-			return
-		}
-		c._state.Store(state)
-	}
 }
 
 // reaper closes idle connections to the cluster.
@@ -789,8 +811,13 @@ func (c *ClusterClient) txPipelineExec(cmds []Cmder) error {
 		return err
 	}
 
+	state := c.state()
+	if state == nil {
+		return errNilClusterState
+	}
+
 	for slot, cmds := range cmdsMap {
-		node, err := c.state().slotMasterNode(slot)
+		node, err := state.slotMasterNode(slot)
 		if err != nil {
 			setCmdsErr(cmds, err)
 			continue

cluster_test.go

@@ -578,7 +578,7 @@ var _ = Describe("ClusterClient timeout", func() {
 	var client *redis.ClusterClient
 
 	AfterEach(func() {
-		Expect(client.Close()).NotTo(HaveOccurred())
+		_ = client.Close()
 	})
 
 	testTimeout := func() {