Fix sentinel leak

Author: vmihailenco

sentinel.go

@@ -301,6 +301,19 @@ func (c *sentinelFailover) Close() error {
 	return nil
 }
 
+func (c *sentinelFailover) closeSentinel() error {
+	firstErr := c.pubsub.Close()
+	c.pubsub = nil
+
+	err := c.sentinel.Close()
+	if err != nil && firstErr == nil {
+		firstErr = err
+	}
+	c.sentinel = nil
+
+	return firstErr
+}
+
 func (c *sentinelFailover) Pool() *pool.ConnPool {
 	c.poolOnce.Do(func() {
 		opt := *c.opt
@@ -331,14 +344,28 @@ func (c *sentinelFailover) MasterAddr() (string, error) {
 }
 
 func (c *sentinelFailover) masterAddr() (string, error) {
-	addr := c.getMasterAddr()
-	if addr != "" {
-		return addr, nil
+	c.mu.RLock()
+	sentinel := c.sentinel
+	c.mu.RUnlock()
+
+	if sentinel != nil {
+		addr := c.getMasterAddr(sentinel)
+		if addr != "" {
+			return addr, nil
+		}
 	}
 
 	c.mu.Lock()
 	defer c.mu.Unlock()
 
+	if c.sentinel != nil {
+		addr := c.getMasterAddr(c.sentinel)
+		if addr != "" {
+			return addr, nil
+		}
+		_ = c.closeSentinel()
+	}
+
 	for i, sentinelAddr := range c.sentinelAddrs {
 		sentinel := NewSentinelClient(&Options{
 			Addr: sentinelAddr,
@@ -378,27 +405,13 @@ func (c *sentinelFailover) masterAddr() (string, error) {
 	return "", errors.New("redis: all sentinels are unreachable")
 }
 
-func (c *sentinelFailover) getMasterAddr() string {
-	c.mu.RLock()
-	sentinel := c.sentinel
-	c.mu.RUnlock()
-
-	if sentinel == nil {
-		return ""
-	}
-
+func (c *sentinelFailover) getMasterAddr(sentinel *SentinelClient) string {
 	addr, err := sentinel.GetMasterAddrByName(c.masterName).Result()
 	if err != nil {
 		internal.Logger.Printf("sentinel: GetMasterAddrByName name=%q failed: %s",
 			c.masterName, err)
-		c.mu.Lock()
-		if c.sentinel == sentinel {
-			_ = c.closeSentinel()
-		}
-		c.mu.Unlock()
 		return ""
 	}
-
 	return net.JoinHostPort(addr[0], addr[1])
 }
 
@@ -413,6 +426,10 @@ func (c *sentinelFailover) switchMaster(addr string) {
 	c.mu.Lock()
 	defer c.mu.Unlock()
 
+	if c._masterAddr == addr {
+		return
+	}
+
 	internal.Logger.Printf("sentinel: new master=%q addr=%q",
 		c.masterName, addr)
 	_ = c.Pool().Filter(func(cn *pool.Conn) bool {
@@ -422,28 +439,18 @@ func (c *sentinelFailover) switchMaster(addr string) {
 }
 
 func (c *sentinelFailover) setSentinel(sentinel *SentinelClient) {
-	c.discoverSentinels(sentinel)
+	if c.sentinel != nil {
+		panic("not reached")
+	}
 	c.sentinel = sentinel
+	c.discoverSentinels()
 
 	c.pubsub = sentinel.Subscribe("+switch-master")
 	go c.listen(c.pubsub)
 }
 
-func (c *sentinelFailover) closeSentinel() error {
-	firstErr := c.pubsub.Close()
-	c.pubsub = nil
-
-	err := c.sentinel.Close()
-	if err != nil && firstErr == nil {
-		firstErr = err
-	}
-	c.sentinel = nil
-
-	return firstErr
-}
-
-func (c *sentinelFailover) discoverSentinels(sentinel *SentinelClient) {
-	sentinels, err := sentinel.Sentinels(c.masterName).Result()
+func (c *sentinelFailover) discoverSentinels() {
+	sentinels, err := c.sentinel.Sentinels(c.masterName).Result()
 	if err != nil {
 		internal.Logger.Printf("sentinel: Sentinels master=%q failed: %s", c.masterName, err)
 		return