问执行并行实体框架查询出错

EN

A second operation started on this context before a previous operation completed. Any instance members are not guaranteed to be thread safe

try
            {

                using (_Context)
                {
                    List<AllotedQuotas> allotedQuotas = new List<AllotedQuotas>();
                    List<Quotas> quotas = new List<Quotas>();

                    Thread t1 = new Thread(() =>
                    {
                        AllotedQuotas ob = new AllotedQuotas(_Context);
                        allotedQuotas = ob.GetAllotedQuotas(pid);
                    });
                    Thread t2 = new Thread(() =>
                    {
                        quotas = _Context._quotas.ToList();
                    });
                    t1.Start();
                    t2.Start();
                    t1.Join();
                    t2.Join();
                    var QuotasList = quotas.Join(allotedQuotas, QID => QID.ID, AID => AID.Quota_ID,
                        (_QutasName, _Alloted) => new Quotas
                        {
                            ID = _QutasName.ID,
                            Quota_Name = _QutasName.Quota_Name,
                            Active = _QutasName.Active
                        }).ToList();
                    return QuotasList;

                }
            }
            catch (Exception ex)
            {
                throw ex.InnerException ?? ex;
            }