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  • ADO.NET中异步处理的方式——Wait方式

    Wait方式使用方法
          三种方式中最好的一种不是Poll方式，也不是回调方式，而是Wait方式。该方式提供的灵活性最大、效率最高，但有点复杂。使用这种方式，可以编写代码，启动多个异步进程，等待全部或部分进程的完成。这种方式允许只等待互相依赖的进程，然后继续执行不互相依赖的进程。按照其设计，这种方式需要仔细考虑异步进程。必须认真选择出以并行方式运行的异步进程，最重要的是，确定不同的进程如何相互依赖。这种方式的复杂性在于，需要理解其中的细节，并设计出相应的代码。最终结果一般是，非常简洁的代码设计能最大限度地利用同步和异步处理模型。
    用代码说明。

     在页面上放两个Gridview用于显示数据。

    代码
    <body>
            <form id="form1" runat="server">
            <div>
                <asp:GridView ID="gvOrders" runat="server" AutoGenerateColumns="false">
                    <Columns>
                        <asp:BoundField HeaderText="Comany Name" DataField="CompanyName" />
                        <asp:BoundField HeaderText="Contact Name" DataField="ContactName" />
                        <asp:BoundField HeaderText="Contact Title" DataField="ContactTitle" />
                        <asp:BoundField HeaderText="Order Date" DataField="OrderDate" DataFormatString="{0:d}" />
                    </Columns>
                </asp:GridView>
            </div>
            <br />
            <div>
                <asp:GridView ID="gvCustomers" runat="server">
                </asp:GridView>
            </div>
            </form>
    </body>


     使用Wait方式取出数据

    using System.Data;
    using System.Data.SqlClient;
    using System.Configuration;

    namespace AdoAsyncDB
    {
            /// <summary>
            /// 使用Wait方式
            /// </summary>
        public partial class WaitMethod : System.Web.UI.Page
        {
                protected void Page_Load(object sender, EventArgs e)
            {
                GetWaitAnyData();
            }

                /// <summary>
                /// 使用Wait方式
                /// 等待句柄关联到异步进程上。使此这种方式，可以启动需要的所有异步进程，等待全部或部分进程的完成，以便对它们执行相应的处理。
                /// 使用这种方式，可以编写代码，启动多个异步进程，等待全部或部分进程的完成。这个方式允许只等待互相依赖的进程，然后继续执行不互相依赖的进程。
                /// </summary>
            private void GetWaitData()
            {
                SqlConnection DBCon;
                SqlCommand Command     = new SqlCommand();
                SqlDataReader OrdersReader;
                IAsyncResult AsyncResult;
                System.Threading.WaitHandle WHandle;

                DBCon     = new SqlConnection();
                DBCon.ConnectionString     = ConfigurationManager.ConnectionStrings["NorthWindDB"].ConnectionString;
                Command.CommandText     = @"select top 50 Customers.CompanyName,Customers.ContactName,customers.ContactTitle,
                                orders.OrderID,Orders.OrderDate,Orders.RequiredDate,orders.ShippedDate
                                from Orders,Customers
                                where Orders.CustomerID=customers.CustomerID
                                order by customers.CompanyName,customers.ContactName    ";
                Command.CommandType     = CommandType.Text;
                Command.Connection     = DBCon;
                DBCon.Open();
                AsyncResult     = Command.BeginExecuteReader();

                WHandle     = AsyncResult.AsyncWaitHandle;

                    if (WHandle.WaitOne() == true)
                {
                    OrdersReader     = Command.EndExecuteReader(AsyncResult);
                    gvOrders.DataSource     = OrdersReader;
                    gvOrders.DataBind();
                    DBCon.Close();
                }
                    else
                {
                        //Asynchronous process has time out.Handle this situation here.
                }
            }

                /// <summary>
                /// 使用多个等待句柄,等待全部
                /// </summary>
            private void GetWaitAllData()
            {
                SqlConnection DBCon;
                SqlCommand OrdersCommand     = new SqlCommand();
                SqlCommand CustCommand     = new SqlCommand();
                SqlDataReader OrdersReader;
                SqlDataReader CustReader;
                IAsyncResult OrdersAsyncResult;
                IAsyncResult CustAsyncResult;

                System.Threading.WaitHandle[] WHandles     = new System.Threading.WaitHandle[2];
                System.Threading.WaitHandle OrdersWHandle;
                System.Threading.WaitHandle CustWHandle;


                DBCon     = new SqlConnection();
                DBCon.ConnectionString     = ConfigurationManager.ConnectionStrings["NorthWindDB"].ConnectionString;

                CustCommand.CommandText     = "select * from customers where companyName='Alfreds Futterkiste'";
                CustCommand.CommandType     = CommandType.Text;
                CustCommand.Connection     = DBCon;


                OrdersCommand.CommandText     = @"select top 50 Customers.CompanyName,Customers.ContactName,customers.ContactTitle,
                                orders.OrderID,Orders.OrderDate,Orders.RequiredDate,orders.ShippedDate
                                from Orders,Customers
                                where Orders.CustomerID=customers.CustomerID
                                order by customers.CompanyName,customers.ContactName    ";
                OrdersCommand.CommandType     = CommandType.Text;
                OrdersCommand.Connection     = DBCon;

                DBCon.Open();

                CustAsyncResult     = CustCommand.BeginExecuteReader();
                OrdersAsyncResult     = OrdersCommand.BeginExecuteReader();

                CustWHandle     = CustAsyncResult.AsyncWaitHandle;
                OrdersWHandle     =     OrdersAsyncResult.AsyncWaitHandle;

                WHandles[    0] = CustWHandle;
                WHandles[    1] = OrdersWHandle;

                System.Threading.WaitHandle.WaitAll(WHandles);

                CustReader     = CustCommand.EndExecuteReader(CustAsyncResult);
                OrdersReader     =     OrdersCommand.EndExecuteReader(OrdersAsyncResult);

                gvCustomers.DataSource     = CustReader;
                gvCustomers.DataBind();

                gvOrders.DataSource     = OrdersReader;
                gvOrders.DataBind();

                DBCon.Close();
            }


                /// <summary>
                /// 使用多个等待句柄,等待部分
                /// </summary>
            private void GetWaitAnyData()
            {
                SqlConnection DBCon;
                SqlCommand OrdersCommand     = new SqlCommand();
                SqlCommand CustCommand     = new SqlCommand();
                SqlDataReader OrdersReader;
                SqlDataReader CustReader;
                IAsyncResult OrdersAsyncResult;
                IAsyncResult CustAsyncResult;

                    int WHindex;
                System.Threading.WaitHandle[] WHandles     = new System.Threading.WaitHandle[2];
                System.Threading.WaitHandle OrdersWHandle;
                System.Threading.WaitHandle CustWHandle;


                DBCon     = new SqlConnection();
                DBCon.ConnectionString     = ConfigurationManager.ConnectionStrings["NorthWindDB"].ConnectionString;

                CustCommand.CommandText     = "select * from customers where companyName='Alfreds Futterkiste'";
                CustCommand.CommandType     = CommandType.Text;
                CustCommand.Connection     = DBCon;


                OrdersCommand.CommandText     = @"select top 5 Customers.CompanyName,Customers.ContactName,customers.ContactTitle,
                                orders.OrderID,Orders.OrderDate,Orders.RequiredDate,orders.ShippedDate
                                from Orders,Customers
                                where Orders.CustomerID=customers.CustomerID
                                order by customers.CompanyName,customers.ContactName    ";
                OrdersCommand.CommandType     = CommandType.Text;
                OrdersCommand.Connection     = DBCon;

                DBCon.Open();

                CustAsyncResult     = CustCommand.BeginExecuteReader();
                OrdersAsyncResult     = OrdersCommand.BeginExecuteReader();

                CustWHandle     = CustAsyncResult.AsyncWaitHandle;
                OrdersWHandle     = OrdersAsyncResult.AsyncWaitHandle;

                WHandles[    0] = CustWHandle;
                WHandles[    1] = OrdersWHandle;


                    for (int Index = 0; Index < 2; Index++)
                {
                    WHindex     = System.Threading.WaitHandle.WaitAny(WHandles);
                        switch (WHindex)
                    {
                            case 0:
                            CustReader     = CustCommand.EndExecuteReader(CustAsyncResult);
                            gvCustomers.DataSource     = CustReader;
                            gvCustomers.DataBind();
                                break;
                            case 1:
                            OrdersReader     = OrdersCommand.EndExecuteReader(OrdersAsyncResult);
                            gvOrders.DataSource     = OrdersReader;
                            gvOrders.DataBind();
                                break;
                            default:
                                break    ;
                    }
                }

                DBCon.Close();
            }
        }
    }


     
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  • 原文地址：https://www.cnblogs.com/scottckt/p/1955294.html
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