// markDown closes conn and temporarily marks the associated
// end point as unusable.
func (sdc *ShardConn) markDown(conn tabletconn.TabletConn, reason string) {
sdc.mu.Lock()
defer sdc.mu.Unlock()
if conn != sdc.conn {
return
}
sdc.balancer.MarkDown(conn.EndPoint().Uid, reason)
go func(conn tabletconn.TabletConn) {
danglingTabletConn.Add(1)
conn.Close()
danglingTabletConn.Add(-1)
}(sdc.conn)
sdc.conn = nil
}