在Application_start()中：
DataTable DT=new DataTable();
DT.Columns.Add("UID",typeof(string));
DataColumn[] PK=new DataColumn[1];
PK[0]=DT.Columns["UID"];
DT.PrimaryKey=PK;
Application["DT"]=DT;
在session_end()中:
Application.Lock();
for(int i=0;i<((DataTable)Application["DT"]).Rows.Count;i++){
DataRow Row=((DataTable)Application["DT"]).Rows;
if(Row["UID"].ToString()==Session["uid"].ToString()){
Row.Delete();
}
}
Application.UnLock();
登录时：
if(((DataTable)Application["DT"]).Rows.Count>0){
if(((DataTable)Application["DT"]).Rows.Contains(uid.Text.Trim())){
Page.RegisterStartupScript("","<script>alert('对不起,已有帐号登入!');</script>");
return;
}
}
