address a deadlock in Conn.Close()

Signed-off-by: Yaroslav Kolomiiets <[email protected]>

conn.go

@@ -900,7 +900,12 @@ func (c *Conn) queueRequest(opcode int32, req interface{}, res interface{}, recv
 	switch opcode {
 	case opClose:
 		// always attempt to send close ops.
-		c.sendChan <- rq
+		select {
+		case c.sendChan <- rq:
+		case <-time.After(c.connectTimeout * 2):
+			c.logger.Printf("gave up trying to send opClose to server")
+			rq.recvChan <- response{-1, ErrConnectionClosed}
+		}
 	default:
 		// otherwise avoid deadlocks for dumb clients who aren't aware that
 		// the ZK connection is closed yet.

conn_test.go

@@ -55,3 +55,28 @@ func TestRecurringReAuthHang(t *testing.T) {
 		t.Fatal(ctx.Err())
 	}
 }
+
+func TestDeadlockInClose(t *testing.T) {
+	c := &Conn{
+		shouldQuit:     make(chan struct{}),
+		connectTimeout: 1 * time.Second,
+		sendChan:       make(chan *request, sendChanSize),
+		logger:         DefaultLogger,
+	}
+
+	for i := 0; i < sendChanSize; i++ {
+		c.sendChan <- &request{}
+	}
+
+	okChan := make(chan struct{})
+	go func() {
+		c.Close()
+		close(okChan)
+	}()
+
+	select {
+	case <-okChan:
+	case <-time.After(3 * time.Second):
+		t.Fatal("apparent deadlock!")
+	}
+}