Fix cmd info race. Fixes redis#578

.travis.yml

@@ -16,5 +16,6 @@ matrix:
     - go: tip
 
 install:
+  - go get go4.org/syncutil
   - go get github.com/onsi/ginkgo
   - go get github.com/onsi/gomega

cluster.go

@@ -7,6 +7,8 @@ import (
 	"sync/atomic"
 	"time"
 
+	"go4.org/syncutil"
+
 	"github.com/go-redis/redis/internal"
 	"github.com/go-redis/redis/internal/hashtag"
 	"github.com/go-redis/redis/internal/pool"
@@ -335,10 +337,12 @@ type ClusterClient struct {
 	cmdable
 
 	opt    *ClusterOptions
-	cmds   map[string]*CommandInfo
 	nodes  *clusterNodes
 	_state atomic.Value
 
+	cmdsInfoOnce syncutil.Once
+	cmdsInfo     map[string]*CommandInfo
+
 	// Reports where slots reloading is in progress.
 	reloading uint32
 }
@@ -389,13 +393,34 @@ func (c *ClusterClient) state() *clusterState {
 	return nil
 }
 
+func (c *ClusterClient) cmdInfo(name string) *CommandInfo {
+	err := c.cmdsInfoOnce.Do(func() error {
+		node, err := c.nodes.Random()
+		if err != nil {
+			return err
+		}
+
+		cmdsInfo, err := node.Client.Command().Result()
+		if err != nil {
+			return err
+		}
+
+		c.cmdsInfo = cmdsInfo
+		return nil
+	})
+	if err != nil {
+		return nil
+	}
+	return c.cmdsInfo[name]
+}
+
 func (c *ClusterClient) cmdSlotAndNode(state *clusterState, cmd Cmder) (int, *clusterNode, error) {
 	if state == nil {
 		node, err := c.nodes.Random()
 		return 0, node, err
 	}
 
-	cmdInfo := c.cmds[cmd.Name()]
+	cmdInfo := c.cmdInfo(cmd.Name())
 	firstKey := cmd.arg(cmdFirstKeyPos(cmd, cmdInfo))
 	slot := hashtag.Slot(firstKey)
 
@@ -631,15 +656,6 @@ func (c *ClusterClient) reloadSlots() (*clusterState, error) {
 		return nil, err
 	}
 
-	// TODO: fix race
-	if c.cmds == nil {
-		cmds, err := node.Client.Command().Result()
-		if err != nil {
-			return nil, err
-		}
-		c.cmds = cmds
-	}
-
 	slots, err := node.Client.ClusterSlots().Result()
 	if err != nil {
 		return nil, err

ring.go

@@ -9,6 +9,8 @@ import (
 	"sync/atomic"
 	"time"
 
+	"go4.org/syncutil"
+
 	"github.com/go-redis/redis/internal"
 	"github.com/go-redis/redis/internal/consistenthash"
 	"github.com/go-redis/redis/internal/hashtag"
@@ -134,7 +136,7 @@ type Ring struct {
 	hash   *consistenthash.Map
 	shards map[string]*ringShard
 
-	cmdsInfoOnce *sync.Once
+	cmdsInfoOnce syncutil.Once
 	cmdsInfo     map[string]*CommandInfo
 
 	closed bool
@@ -149,8 +151,6 @@ func NewRing(opt *RingOptions) *Ring {
 
 		hash:   consistenthash.New(nreplicas, nil),
 		shards: make(map[string]*ringShard),
-
-		cmdsInfoOnce: new(sync.Once),
 	}
 	ring.setProcessor(ring.Process)
 	for name, addr := range opt.Addrs {
@@ -242,17 +242,21 @@ func (c *Ring) ForEachShard(fn func(client *Client) error) error {
 }
 
 func (c *Ring) cmdInfo(name string) *CommandInfo {
-	c.cmdsInfoOnce.Do(func() {
+	err := c.cmdsInfoOnce.Do(func() error {
+		var firstErr error
 		for _, shard := range c.shards {
 			cmdsInfo, err := shard.Client.Command().Result()
 			if err == nil {
 				c.cmdsInfo = cmdsInfo
-				return
+				return nil
+			}
+			if firstErr == nil {
+				firstErr = err
 			}
 		}
-		c.cmdsInfoOnce = &sync.Once{}
+		return firstErr
 	})
-	if c.cmdsInfo == nil {
+	if err != nil {
 		return nil
 	}
 	return c.cmdsInfo[name]