不重复订单号生成规则

public class BillNumberBuilder{
    private static object locker = new object();
     
    private static int sn = 0;
     
    public static string NextBillNumber(){
        lock(locker){
            if(sn == 9999999999)
                sn = 0;
            else
                sn++;
            return DateTime.Now.ToString("yyyyMMddHHmmss") + sn.ToString().PadLeft(10, ‘0‘);
        }
    }
    // 防止创建类的实例
    private BillNumberBuilder(){}
}