使用等待句柄的 ASP.NET 应用程序
当应用程序一次只处理一个异步操作时，用于处理异步操作的回调和轮询模型将非常有用。 Wait 模型提供了一种更灵活的方法来处理多个异步操作。 有两种 Wait 模型，是根据用于实现它们的 WaitHandle 方法命名的：Wait (Any) 模型和 Wait (All) 模型。
若要使用任一 Wait 模型，需要使用 BeginExecuteNonQuery、BeginExecuteReader 或 BeginExecuteXmlReader 方法返回的 IAsyncResult 对象的 AsyncWaitHandle 属性。 WaitAny 和 WaitAll 方法都需要将 WaitHandle 对象作为参数发送，并分组到一个数组中。
两个 Wait 方法都监视异步操作，等待完成。 WaitAny 方法会等待任何操作完成或超时。一旦你知道特定操作已完成，就可以处理其结果，然后继续等待下一个操作完成或超时。WaitAll 方法会在继续之前等待一系列 WaitHandle 实例中的所有进程完成或超时。
当需要在不同的服务器上运行不同长度的多个操作时，或者当服务器的功能足以同时处理所有查询时，Wait 模型的好处最为明显。 在此处介绍的示例中，三个查询通过将不同长度的 WAITFOR 命令添加到无关紧要的 SELECT 查询来模拟长进程。
示例：等待（任何）模型
下例说明了 Wait (Any) 模型。 启动了三个异步进程后，将调用 WaitAny 方法来等待其中任何一个进程完成。 每个进程完成后，将调用 EndExecuteReader 方法，并读取生成的 SqlDataReader 对象。 此时，实际应用程序很可能会使用 SqlDataReader 来填充部分页面。 在这个简单的示例中，将进程完成的时间添加到与该进程相对应的文本框中。 合起来看，文本框中的这些时间说明以下结论：每次进程完成后都执行代码。
若要设置此示例，请创建新的 ASP.NET 网站项目。 将一个 Button 控件和四个 TextBox 控件置于该页（接受每个控件的默认名称）。
将以下代码添加到窗体的类中，根据环境的需要修改连接字符串。
' Add these to the top of the class
Imports System
Imports System.Data
Imports System.Data.SqlClient
Imports System.Threading
' Add this code to the page's class:
Private Function GetConnectionString() As String
' To avoid storing the connection string in your code,
' you can retrieve it from a configuration file.
' If you have not included "Asynchronous Processing=true"
' in the connection string, the command will not be able
' to execute asynchronously.
Return "..." & _
"Asynchronous Processing=true"
End Function
Sub Button1_Click( _
ByVal sender As Object, ByVal e As System.EventArgs)
' In a real-world application, you might be connecting to
' three different servers or databases. For the example,
' we connect to only one.
Dim connection1 As New SqlConnection(GetConnectionString())
Dim connection2 As New SqlConnection(GetConnectionString())
Dim connection3 As New SqlConnection(GetConnectionString())
' To keep the example simple, all three asynchronous
' processes select a row from the same table. WAITFOR
' commands are used to emulate long-running processes
' that complete after different periods of time.
Dim commandText1 As String = _
"WAITFOR DELAY '0:0:01';" & _
"SELECT * FROM Production.Product " & _
"WHERE ProductNumber = 'BL-2036'"
Dim commandText2 As String = _
"WAITFOR DELAY '0:0:05';" & _
"SELECT * FROM Production.Product " & _
"WHERE ProductNumber = 'BL-2036'"
Dim commandText3 As String = _
"WAITFOR DELAY '0:0:10';" & _
"SELECT * FROM Production.Product " & _
"WHERE ProductNumber = 'BL-2036'"
Dim waitHandles(2) As WaitHandle
Try
' For each process, open a connection and begin execution.
' Use the IAsyncResult object returned by
' BeginExecuteReader to add a WaitHandle for the process
' to the array.
connection1.Open()
Dim command1 As New SqlCommand(commandText1, connection1)
Dim result1 As IAsyncResult = _
command1.BeginExecuteReader()
waitHandles(0) = result1.AsyncWaitHandle
connection2.Open()
Dim command2 As New SqlCommand(commandText2, connection2)
Dim result2 As IAsyncResult = _
command2.BeginExecuteReader()
waitHandles(1) = result2.AsyncWaitHandle
connection3.Open()
Dim command3 As New SqlCommand(commandText3, connection3)
Dim result3 As IAsyncResult = _
command3.BeginExecuteReader()
waitHandles(2) = result3.AsyncWaitHandle
Dim index As Integer
For countWaits As Integer = 1 To 3
' WaitAny waits for any of the processes to complete.
' The return value is either the index of the
' array element whose process just completed, or
' the WaitTimeout value.
index = WaitHandle.WaitAny(waitHandles, 60000, False)
' This example doesn't actually do anything with the
' data returned by the processes, but the code opens
' readers for each just to demonstrate the concept.
' Instead of using the returned data to fill the
' controls on the page, the example adds the time
' the process was completed to the corresponding
' text box.
Select Case index
Case 0
Dim reader1 As SqlDataReader
reader1 = command1.EndExecuteReader(result1)
If reader1.Read Then
TextBox1.Text = _
"Completed " & _
System.DateTime.Now.ToLongTimeString()
End If
reader1.Close()
Case 1
Dim reader2 As SqlDataReader
reader2 = command2.EndExecuteReader(result2)
If reader2.Read Then
TextBox2.Text = _
"Completed " & _
System.DateTime.Now.ToLongTimeString()
End If
reader2.Close()
Case 2
Dim reader3 As SqlDataReader
reader3 = command3.EndExecuteReader(result3)
If reader3.Read Then
TextBox3.Text = _
"Completed " & _
System.DateTime.Now.ToLongTimeString()
End If
reader3.Close()
Case WaitHandle.WaitTimeout
Throw New Exception("Timeout")
End Select
Next
Catch ex As Exception
TextBox4.Text = ex.ToString
End Try
connection1.Close()
connection2.Close()
connection3.Close()
End Sub
// Add the following using directives, if they aren't already there.
using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Threading;
using System.Data.SqlClient;
// Add this code to the page's class
string GetConnectionString()
// To avoid storing the connection string in your code,
// you can retrieve it from a configuration file.
// If you have not included "Asynchronous Processing=true"
// in the connection string, the command will not be able
// to execute asynchronously.
{
return "/* Rest of connection string */" + "Asynchronous Processing=true";
}
void Button1_Click(object sender, System.EventArgs e)
{
// In a real-world application, you might be connecting to
// three different servers or databases. For the example,
// we connect to only one.
SqlConnection connection1 =
new SqlConnection(GetConnectionString());
SqlConnection connection2 =
new SqlConnection(GetConnectionString());
SqlConnection connection3 =
new SqlConnection(GetConnectionString());
// To keep the example simple, all three asynchronous
// processes select a row from the same table. WAITFOR
// commands are used to emulate long-running processes
// that complete after different periods of time.
string commandText1 = "WAITFOR DELAY '0:0:01';" +
"SELECT * FROM Production.Product " +
"WHERE ProductNumber = 'BL-2036'";
string commandText2 = "WAITFOR DELAY '0:0:05';" +
"SELECT * FROM Production.Product " +
"WHERE ProductNumber = 'BL-2036'";
string commandText3 = "WAITFOR DELAY '0:0:10';" +
"SELECT * FROM Production.Product " +
"WHERE ProductNumber = 'BL-2036'";
try
// For each process, open a connection and begin
// execution. Use the IAsyncResult object returned by
// BeginExecuteReader to add a WaitHandle for the
// process to the array.
{
connection1.Open();
SqlCommand command1 =
new SqlCommand(commandText1, connection1);
IAsyncResult result1 = command1.BeginExecuteReader();
WaitHandle waitHandle1 = result1.AsyncWaitHandle;
connection2.Open();
SqlCommand command2 =
new SqlCommand(commandText2, connection2);
IAsyncResult result2 = command2.BeginExecuteReader();
WaitHandle waitHandle2 = result2.AsyncWaitHandle;
connection3.Open();
SqlCommand command3 =
new SqlCommand(commandText3, connection3);
IAsyncResult result3 = command3.BeginExecuteReader();
WaitHandle waitHandle3 = result3.AsyncWaitHandle;
WaitHandle[] waitHandles = {
waitHandle1, waitHandle2, waitHandle3
};
int index;
for (int countWaits = 0; countWaits <= 2; countWaits++)
{
// WaitAny waits for any of the processes to
// complete. The return value is either the index
// of the array element whose process just
// completed, or the WaitTimeout value.
index = WaitHandle.WaitAny(waitHandles,
60000, false);
// This example doesn't actually do anything with
// the data returned by the processes, but the
// code opens readers for each just to demonstrate
// the concept.
// Instead of using the returned data to fill the
// controls on the page, the example adds the time
// the process was completed to the corresponding
// text box.
switch (index)
{
case 0:
SqlDataReader reader1;
reader1 =
command1.EndExecuteReader(result1);
if (reader1.Read())
{
TextBox1.Text =
"Completed " +
System.DateTime.Now.ToLongTimeString();
}
reader1.Close();
break;
case 1:
SqlDataReader reader2;
reader2 =
command2.EndExecuteReader(result2);
if (reader2.Read())
{
TextBox2.Text =
"Completed " +
System.DateTime.Now.ToLongTimeString();
}
reader2.Close();
break;
case 2:
SqlDataReader reader3;
reader3 =
command3.EndExecuteReader(result3);
if (reader3.Read())
{
TextBox3.Text =
"Completed " +
System.DateTime.Now.ToLongTimeString();
}
reader3.Close();
break;
case WaitHandle.WaitTimeout:
throw new Exception("Timeout");
break;
}
}
}
catch (Exception ex)
{
TextBox4.Text = ex.ToString();
}
connection1.Close();
connection2.Close();
connection3.Close();
}
示例：等待（所有）模型
下例说明了 Wait (All) 模型。 启动了三个异步进程后，将调用 WaitAll 方法以等待进程完成或超时。
与 Wait (Any) 模型的示例类似，进程完成的时间将添加到与该进程相对应的文本框中。 文本框中的这些时间再次说明以下结论：跟随在 WaitAny 方法后的代码只在所有进程都完成后才执行。
若要设置此示例，请创建新的 ASP.NET 网站项目。 将一个 Button 控件和四个 TextBox 控件置于该页（接受每个控件的默认名称）。
将以下代码添加到窗体的类中，根据环境的需要修改连接字符串。
' Add these to the top of the class
Imports System
Imports System.Data
Imports System.Data.SqlClient
Imports System.Threading
' Add this code to the page's class:
Private Function GetConnectionString() As String
' To avoid storing the connection string in your code,
' you can retrieve it from a configuration file.
' If you have not included "Asynchronous Processing=true"
' in the connection string, the command will not be able
' to execute asynchronously.
Return "..." & _
"Asynchronous Processing=true"
End Function
Sub Button1_Click( _
ByVal sender As Object, ByVal e As System.EventArgs)
' In a real-world application, you might be connecting to
' three different servers or databases. For the example,
' we connect to only one.
Dim connection1 As New SqlConnection(GetConnectionString())
Dim connection2 As New SqlConnection(GetConnectionString())
Dim connection3 As New SqlConnection(GetConnectionString())
' To keep the example simple, all three asynchronous
' processes select a row from the same table. WAITFOR
' commands are used to emulate long-running processes
' that complete after different periods of time.
Dim commandText1 As String = _
"UPDATE Production.Product " & _
"SET ReorderPoint = ReorderPoint + 1 " & _
"WHERE ReorderPoint Is Not Null;" & _
"WAITFOR DELAY '0:0:01';" & _
"UPDATE Production.Product " & _
"SET ReorderPoint = ReorderPoint - 1 " & _
"WHERE ReorderPoint Is Not Null"
Dim commandText2 As String = _
"UPDATE Production.Product " & _
"SET ReorderPoint = ReorderPoint + 1 " & _
"WHERE ReorderPoint Is Not Null;" & _
"WAITFOR DELAY '0:0:05';" & _
"UPDATE Production.Product " & _
"SET ReorderPoint = ReorderPoint - 1 " & _
"WHERE ReorderPoint Is Not Null"
Dim commandText3 As String = _
"UPDATE Production.Product " & _
"SET ReorderPoint = ReorderPoint + 1 " & _
"WHERE ReorderPoint Is Not Null;" & _
"WAITFOR DELAY '0:0:10';" & _
"UPDATE Production.Product " & _
"SET ReorderPoint = ReorderPoint - 1 " & _
"WHERE ReorderPoint Is Not Null"
Dim waitHandles(2) As WaitHandle
Try
' For each process, open a connection and begin execution.
' Use the IAsyncResult object returned by
' BeginExecuteReader to add a WaitHandle for the process
' to the array.
connection1.Open()
Dim command1 As New SqlCommand(commandText1, connection1)
Dim result1 As IAsyncResult = _
command1.BeginExecuteNonQuery()
waitHandles(0) = result1.AsyncWaitHandle
connection2.Open()
Dim command2 As New SqlCommand(commandText2, connection2)
Dim result2 As IAsyncResult = _
command2.BeginExecuteNonQuery()
waitHandles(1) = result2.AsyncWaitHandle
connection3.Open()
Dim command3 As New SqlCommand(commandText3, connection3)
Dim result3 As IAsyncResult = _
command3.BeginExecuteNonQuery()
waitHandles(2) = result3.AsyncWaitHandle
' WaitAll waits for all of the processes to complete.
' The return value is True if all processes completed,
' False if any process timed out.
Dim result As Boolean = _
WaitHandle.WaitAll(waitHandles, 60000, False)
If result Then
Dim rowCount1 As Long = _
command1.EndExecuteNonQuery(result1)
TextBox1.Text = _
"Completed " & _
System.DateTime.Now.ToLongTimeString()
Dim rowCount2 As Long = _
command2.EndExecuteNonQuery(result2)
TextBox2.Text = _
"Completed " & _
System.DateTime.Now.ToLongTimeString()
Dim rowCount3 As Long = _
command3.EndExecuteNonQuery(result3)
TextBox3.Text = _
"Completed " & _
System.DateTime.Now.ToLongTimeString()
Else
Throw New Exception("Timeout")
End If
Catch ex As Exception
TextBox4.Text = ex.ToString
End Try
connection1.Close()
connection2.Close()
connection3.Close()
End Sub
// Add the following using directives, if they aren't already there.
using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Threading;
using System.Data.SqlClient;
// Add this code to the page's class
string GetConnectionString()
// To avoid storing the connection string in your code,
// you can retrieve it from a configuration file.
// If you have not included "Asynchronous Processing=true"
// in the connection string, the command will not be able
// to execute asynchronously.
{
return "..." +
"Asynchronous Processing=true";
}
void Button1_Click(object sender, System.EventArgs e)
{
// In a real-world application, you might be connecting to
// three different servers or databases. For the example,
// we connect to only one.
SqlConnection connection1 =
new SqlConnection(GetConnectionString());
SqlConnection connection2 =
new SqlConnection(GetConnectionString());
SqlConnection connection3 =
new SqlConnection(GetConnectionString());
// To keep the example simple, all three asynchronous
// processes execute UPDATE queries that result in
// no change to the data. WAITFOR
// commands are used to emulate long-running processes
// that complete after different periods of time.
string commandText1 =
"UPDATE Production.Product " +
"SET ReorderPoint = ReorderPoint + 1 " +
"WHERE ReorderPoint Is Not Null;" +
"WAITFOR DELAY '0:0:01';" +
"UPDATE Production.Product " +
"SET ReorderPoint = ReorderPoint - 1 " +
"WHERE ReorderPoint Is Not Null";
string commandText2 =
"UPDATE Production.Product " +
"SET ReorderPoint = ReorderPoint + 1 " +
"WHERE ReorderPoint Is Not Null;" +
"WAITFOR DELAY '0:0:05';" +
"UPDATE Production.Product " +
"SET ReorderPoint = ReorderPoint - 1 " +
"WHERE ReorderPoint Is Not Null";
string commandText3 =
"UPDATE Production.Product " +
"SET ReorderPoint = ReorderPoint + 1 " +
"WHERE ReorderPoint Is Not Null;" +
"WAITFOR DELAY '0:0:10';" +
"UPDATE Production.Product " +
"SET ReorderPoint = ReorderPoint - 1 " +
"WHERE ReorderPoint Is Not Null";
try
// For each process, open a connection and begin
// execution. Use the IAsyncResult object returned by
// BeginExecuteReader to add a WaitHandle for the
// process to the array.
{
connection1.Open();
SqlCommand command1 =
new SqlCommand(commandText1, connection1);
IAsyncResult result1 = command1.BeginExecuteNonQuery();
WaitHandle waitHandle1 = result1.AsyncWaitHandle;
connection2.Open();
SqlCommand command2 =
new SqlCommand(commandText2, connection2);
IAsyncResult result2 = command2.BeginExecuteNonQuery();
WaitHandle waitHandle2 = result2.AsyncWaitHandle;
connection3.Open();
SqlCommand command3 =
new SqlCommand(commandText3, connection3);
IAsyncResult result3 = command3.BeginExecuteNonQuery();
WaitHandle waitHandle3 = result3.AsyncWaitHandle;
WaitHandle[] waitHandles = {
waitHandle1, waitHandle2, waitHandle3
};
bool result;
// WaitAll waits for all of the processes to
// complete. The return value is True if the processes
// all completed successfully, False if any process
// timed out.
result = WaitHandle.WaitAll(waitHandles, 60000, false);
if(result)
{
long rowCount1 =
command1.EndExecuteNonQuery(result1);
TextBox1.Text = "Completed " +
System.DateTime.Now.ToLongTimeString();
long rowCount2 =
command2.EndExecuteNonQuery(result2);
TextBox2.Text = "Completed " +
System.DateTime.Now.ToLongTimeString();
long rowCount3 =
command3.EndExecuteNonQuery(result3);
TextBox3.Text = "Completed " +
System.DateTime.Now.ToLongTimeString();
}
else
{
throw new Exception("Timeout");
}
}
catch (Exception ex)
{
TextBox4.Text = ex.ToString();
}
connection1.Close();
connection2.Close();
connection3.Close();
}