private async Task NormalConnectionLeaveGroup()
 {
     if (_connections.Count >= _groupCount)
     {
         await Task.WhenAll(from i in Enumerable.Range(0, _connections.Count)
                            select SignalRUtils.LeaveFromGroup(_connections[i],
                                                               SignalRUtils.GroupName(_type,
                                                                                      _connectionIndex[i] % _groupCount),
                                                               _statisticsCollector));
     }
     else
     {
         var connectionCount = _connections.Count;
         await Task.WhenAll(from i in Enumerable.Range(0, _groupCount)
                            select SignalRUtils.LeaveFromGroup(_connections[i % connectionCount],
                                                               SignalRUtils.GroupName(_type, i),
                                                               _statisticsCollector));
     }
 }