clientv3: only start lease stream after first keepalive call

Fixes #7274

clientv3/lease.go

@@ -126,6 +126,9 @@ type lessor struct {
 	// firstKeepAliveTimeout is the timeout for the first keepalive request
 	// before the actual TTL is known to the lease client
 	firstKeepAliveTimeout time.Duration
+
+	// firstKeepAliveOnce ensures stream starts after first KeepAlive call.
+	firstKeepAliveOnce sync.Once
 }
 
 // keepAlive multiplexes a keepalive for a lease over multiple channels
@@ -152,8 +155,6 @@ func NewLease(c *Client) Lease {
 	}
 
 	l.stopCtx, l.stopCancel = context.WithCancel(context.Background())
-	go l.recvKeepAliveLoop()
-	go l.deadlineLoop()
 	return l
 }
 
@@ -254,6 +255,10 @@ func (l *lessor) KeepAlive(ctx context.Context, id LeaseID) (<-chan *LeaseKeepAl
 	l.mu.Unlock()
 
 	go l.keepAliveCtxCloser(id, ctx, ka.donec)
+	l.firstKeepAliveOnce.Do(func() {
+		go l.recvKeepAliveLoop()
+		go l.deadlineLoop()
+	})
 
 	return ch, nil
 }
@@ -279,6 +284,8 @@ func (l *lessor) KeepAliveOnce(ctx context.Context, id LeaseID) (*LeaseKeepAlive
 
 func (l *lessor) Close() error {
 	l.stopCancel()
+	// close for synchronous teardown if stream goroutines never launched
+	l.firstKeepAliveOnce.Do(func() { close(l.donec) })
 	<-l.donec
 	return nil
 }