bug: ensure context isn't exhausted via concurrent query

Author: gnpaone

sentinel.go

@@ -540,7 +540,6 @@ func (c *sentinelFailover) MasterAddr(ctx context.Context) (string, error) {
 			if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {
 				return "", err
 			}
-			// Continue on other errors
 			internal.Logger.Printf(ctx, "sentinel: GetMasterAddrByName name=%q failed: %s",
 				c.opt.MasterName, err)
 		} else {
@@ -558,36 +557,59 @@ func (c *sentinelFailover) MasterAddr(ctx context.Context) (string, error) {
 			if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {
 				return "", err
 			}
-			// Continue on other errors
 			internal.Logger.Printf(ctx, "sentinel: GetMasterAddrByName name=%q failed: %s",
 				c.opt.MasterName, err)
 		} else {
 			return addr, nil
 		}
 	}
 
+	var (
+		masterAddr string
+		wg         sync.WaitGroup
+		once       sync.Once
+		done       = make(chan struct{})
+	)
+
 	for i, sentinelAddr := range c.sentinelAddrs {
-		sentinel := NewSentinelClient(c.opt.sentinelOptions(sentinelAddr))
+		wg.Add(1)
+		go func(i int, addr string) {
+			defer wg.Done()
+			select {
+			case <-done:
+				return
+			default:
+				sentinelCli := NewSentinelClient(c.opt.sentinelOptions(addr))
+				addrVal, err := sentinelCli.GetMasterAddrByName(ctx, c.opt.MasterName).Result()
+				if err != nil {
+					internal.Logger.Printf(ctx, "sentinel: GetMasterAddrByName addr=%s, master=%q failed: %s",
+						addr, c.opt.MasterName, err)
+					_ = sentinelCli.Close()
+					return
+				}
 
-		masterAddr, err := sentinel.GetMasterAddrByName(ctx, c.opt.MasterName).Result()
-		if err != nil {
-			_ = sentinel.Close()
-			if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {
-				return "", err
+				once.Do(func() {
+					masterAddr = net.JoinHostPort(addrVal[0], addrVal[1])
+					// Push working sentinel to the top
+					c.sentinelAddrs[0], c.sentinelAddrs[i] = c.sentinelAddrs[i], c.sentinelAddrs[0]
+					c.setSentinel(ctx, sentinelCli)
+					internal.Logger.Printf(ctx, "sentinel: selected addr=%s masterAddr=%s", addr, masterAddr)
+					close(done)
+				})
 			}
-			internal.Logger.Printf(ctx, "sentinel: GetMasterAddrByName master=%q failed: %s",
-				c.opt.MasterName, err)
-			continue
-		}
+		}(i, sentinelAddr)
+	}
 
-		// Push working sentinel to the top.
-		c.sentinelAddrs[0], c.sentinelAddrs[i] = c.sentinelAddrs[i], c.sentinelAddrs[0]
-		c.setSentinel(ctx, sentinel)
+	go func() {
+		wg.Wait()
+		once.Do(func() { close(done) })
+	}()
 
-		addr := net.JoinHostPort(masterAddr[0], masterAddr[1])
-		return addr, nil
-	}
+	<-done
 
+	if masterAddr != "" {
+		return masterAddr, nil
+	}
 	return "", errors.New("redis: all sentinels specified in configuration are unreachable")
 }