Create PubSub channel once

pubsub.go

@@ -29,6 +29,9 @@ type PubSub struct {
 	closed   bool
 
 	cmd *Cmd
+
+	chOnce sync.Once
+	ch     chan *Message
 }
 
 func (c *PubSub) conn() (*pool.Conn, error) {
@@ -346,10 +349,12 @@ func (c *PubSub) receiveMessage(timeout time.Duration) (*Message, error) {
 	}
 }
 
-// Channel returns a channel for concurrently receiving messages.
+// Channel returns a Go channel for concurrently receiving messages.
-// The channel is closed with PubSub.
+// The channel is closed with PubSub. Receive or ReceiveMessage APIs
+// can not be used after channel is created.
 func (c *PubSub) Channel() <-chan *Message {
-	ch := make(chan *Message, 100)
+	c.chOnce.Do(func() {
+		c.ch = make(chan *Message, 100)
 		go func() {
 			for {
 				msg, err := c.ReceiveMessage()
@@ -359,11 +364,12 @@ func (c *PubSub) Channel() <-chan *Message {
 					}
 					continue
 				}
-			ch <- msg
+				c.ch <- msg
 			}
-		close(ch)
+			close(c.ch)
 		}()
-	return ch
+	})
+	return c.ch
 }
 
 func appendIfNotExists(ss []string, es ...string) []string {