更新：2007 年 11 月
下面的代码示例使用异步方法实现了一个组件（参见 基于事件的异步模式概述）。组件是一个使用埃拉托色尼过滤 (Sieve of Eratosthenes) 算法来确定一个数字是质数还是合数的质数计算器。
Visual Studio 中对此任务提供了广泛的支持。有关更多信息，请参见演练：实现支持基于事件的异步模式的组件 和演练：实现支持基于事件的异步模式的组件 和演练：实现支持基于事件的异步模式的组件.
有关使用 PrimeNumberCalculator 组件的示例客户端，请参见如何：实现基于事件的异步模式的客户端。
示例
Imports System
Imports System.Collections
Imports System.Collections.Specialized
Imports System.ComponentModel
Imports System.Drawing
Imports System.Globalization
Imports System.Threading
Imports System.Windows.Forms
...
Public Delegate Sub ProgressChangedEventHandler( _
ByVal e As ProgressChangedEventArgs)
Public Delegate Sub CalculatePrimeCompletedEventHandler( _
ByVal sender As Object, _
ByVal e As CalculatePrimeCompletedEventArgs)
' This class implements the Event-based Asynchronous Pattern.
' It asynchronously computes whether a number is prime or
' composite (not prime).
Public Class PrimeNumberCalculator
Inherits System.ComponentModel.Component
Private Delegate Sub WorkerEventHandler( _
ByVal numberToCheck As Integer, _
ByVal asyncOp As AsyncOperation)
Private onProgressReportDelegate As SendOrPostCallback
Private onCompletedDelegate As SendOrPostCallback
Private userStateToLifetime As New HybridDictionary()
Private components As System.ComponentModel.Container = Nothing
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
#Region "Public events"
Public Event ProgressChanged _
As ProgressChangedEventHandler
Public Event CalculatePrimeCompleted _
As CalculatePrimeCompletedEventHandler
#End Region
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
#Region "Construction and destruction"
Public Sub New(ByVal container As System.ComponentModel.IContainer)
container.Add(Me)
InitializeComponent()
InitializeDelegates()
End Sub
Public Sub New()
InitializeComponent()
InitializeDelegates()
End Sub
Protected Overridable Sub InitializeDelegates()
onProgressReportDelegate = _
New SendOrPostCallback(AddressOf ReportProgress)
onCompletedDelegate = _
New SendOrPostCallback(AddressOf CalculateCompleted)
End Sub
Protected Overrides Sub Dispose(ByVal disposing As Boolean)
If disposing Then
If (components IsNot Nothing) Then
components.Dispose()
End If
End If
MyBase.Dispose(disposing)
End Sub
#End Region
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
#Region "Implementation"
' This method starts an asynchronous calculation.
' First, it checks the supplied task ID for uniqueness.
' If taskId is unique, it creates a new WorkerEventHandler
' and calls its BeginInvoke method to start the calculation.
Public Overridable Sub CalculatePrimeAsync( _
ByVal numberToTest As Integer, _
ByVal taskId As Object)
' Create an AsyncOperation for taskId.
Dim asyncOp As AsyncOperation = _
AsyncOperationManager.CreateOperation(taskId)
' Multiple threads will access the task dictionary,
' so it must be locked to serialize access.
SyncLock userStateToLifetime.SyncRoot
If userStateToLifetime.Contains(taskId) Then
Throw New ArgumentException( _
"Task ID parameter must be unique", _
"taskId")
End If
userStateToLifetime(taskId) = asyncOp
End SyncLock
' Start the asynchronous operation.
Dim workerDelegate As New WorkerEventHandler( _
AddressOf CalculateWorker)
workerDelegate.BeginInvoke( _
numberToTest, _
asyncOp, _
Nothing, _
Nothing)
End Sub
' Utility method for determining if a
' task has been canceled.
Private Function TaskCanceled(ByVal taskId As Object) As Boolean
Return (userStateToLifetime(taskId) Is Nothing)
End Function
' This method cancels a pending asynchronous operation.
Public Sub CancelAsync(ByVal taskId As Object)
Dim obj As Object = userStateToLifetime(taskId)
If (obj IsNot Nothing) Then
SyncLock userStateToLifetime.SyncRoot
userStateToLifetime.Remove(taskId)
End SyncLock
End If
End Sub
' This method performs the actual prime number computation.
' It is executed on the worker thread.
Private Sub CalculateWorker( _
ByVal numberToTest As Integer, _
ByVal asyncOp As AsyncOperation)
Dim prime As Boolean = False
Dim firstDivisor As Integer = 1
Dim exc As Exception = Nothing
' Check that the task is still active.
' The operation may have been canceled before
' the thread was scheduled.
If Not Me.TaskCanceled(asyncOp.UserSuppliedState) Then
Try
' Find all the prime numbers up to the
' square root of numberToTest.
Dim primes As ArrayList = BuildPrimeNumberList( _
numberToTest, asyncOp)
' Now we have a list of primes less than
'numberToTest.
prime = IsPrime( _
primes, _
numberToTest, _
firstDivisor)
Catch ex As Exception
exc = ex
End Try
End If
Me.CompletionMethod( _
numberToTest, _
firstDivisor, _
prime, _
exc, _
TaskCanceled(asyncOp.UserSuppliedState), _
asyncOp)
End Sub
' This method computes the list of prime numbers used by the
' IsPrime method.
Private Function BuildPrimeNumberList( _
ByVal numberToTest As Integer, _
ByVal asyncOp As AsyncOperation) As ArrayList
Dim e As ProgressChangedEventArgs = Nothing
Dim primes As New ArrayList
Dim firstDivisor As Integer
Dim n As Integer = 5
' Add the first prime numbers.
primes.Add(2)
primes.Add(3)
' Do the work.
While n < numberToTest And _
Not Me.TaskCanceled(asyncOp.UserSuppliedState)
If IsPrime(primes, n, firstDivisor) Then
' Report to the client that you found a prime.
e = New CalculatePrimeProgressChangedEventArgs( _
n, _
CSng(n) / CSng(numberToTest) * 100, _
asyncOp.UserSuppliedState)
asyncOp.Post(Me.onProgressReportDelegate, e)
primes.Add(n)
' Yield the rest of this time slice.
Thread.Sleep(0)
End If
' Skip even numbers.
n += 2
End While
Return primes
End Function
' This method tests n for primality against the list of
' prime numbers contained in the primes parameter.
Private Function IsPrime( _
ByVal primes As ArrayList, _
ByVal n As Integer, _
ByRef firstDivisor As Integer) As Boolean
Dim foundDivisor As Boolean = False
Dim exceedsSquareRoot As Boolean = False
Dim i As Integer = 0
Dim divisor As Integer = 0
firstDivisor = 1
' Stop the search if:
' there are no more primes in the list,
' there is a divisor of n in the list, or
' there is a prime that is larger than
' the square root of n.
While i < primes.Count AndAlso _
Not foundDivisor AndAlso _
Not exceedsSquareRoot
' The divisor variable will be the smallest prime number
' not yet tried.
divisor = primes(i)
i = i + 1
' Determine whether the divisor is greater than the
' square root of n.
If divisor * divisor > n Then
exceedsSquareRoot = True
' Determine whether the divisor is a factor of n.
ElseIf n Mod divisor = 0 Then
firstDivisor = divisor
foundDivisor = True
End If
End While
Return Not foundDivisor
End Function
' This method is invoked via the AsyncOperation object,
' so it is guaranteed to be executed on the correct thread.
Private Sub CalculateCompleted(ByVal operationState As Object)
Dim e As CalculatePrimeCompletedEventArgs = operationState
OnCalculatePrimeCompleted(e)
End Sub
' This method is invoked via the AsyncOperation object,
' so it is guaranteed to be executed on the correct thread.
Private Sub ReportProgress(ByVal state As Object)
Dim e As ProgressChangedEventArgs = state
OnProgressChanged(e)
End Sub
Protected Sub OnCalculatePrimeCompleted( _
ByVal e As CalculatePrimeCompletedEventArgs)
RaiseEvent CalculatePrimeCompleted(Me, e)
End Sub
Protected Sub OnProgressChanged( _
ByVal e As ProgressChangedEventArgs)
RaiseEvent ProgressChanged(e)
End Sub
' This is the method that the underlying, free-threaded
' asynchronous behavior will invoke. This will happen on
' an arbitrary thread.
Private Sub CompletionMethod( _
ByVal numberToTest As Integer, _
ByVal firstDivisor As Integer, _
ByVal prime As Boolean, _
ByVal exc As Exception, _
ByVal canceled As Boolean, _
ByVal asyncOp As AsyncOperation)
' If the task was not previously canceled,
' remove the task from the lifetime collection.
If Not canceled Then
SyncLock userStateToLifetime.SyncRoot
userStateToLifetime.Remove(asyncOp.UserSuppliedState)
End SyncLock
End If
' Package the results of the operation in a
' CalculatePrimeCompletedEventArgs.
Dim e As New CalculatePrimeCompletedEventArgs( _
numberToTest, _
firstDivisor, _
prime, _
exc, _
canceled, _
asyncOp.UserSuppliedState)
' End the task. The asyncOp object is responsible
' for marshaling the call.
asyncOp.PostOperationCompleted(onCompletedDelegate, e)
' Note that after the call to PostOperationCompleted, asyncOp
' is no longer usable, and any attempt to use it will cause.
' an exception to be thrown.
End Sub
#End Region
Private Sub InitializeComponent()
End Sub
End Class
Public Class CalculatePrimeProgressChangedEventArgs
Inherits ProgressChangedEventArgs
Private latestPrimeNumberValue As Integer = 1
Public Sub New( _
ByVal latestPrime As Integer, _
ByVal progressPercentage As Integer, _
ByVal UserState As Object)
MyBase.New(progressPercentage, UserState)
Me.latestPrimeNumberValue = latestPrime
End Sub
Public ReadOnly Property LatestPrimeNumber() As Integer
Get
Return latestPrimeNumberValue
End Get
End Property
End Class
Public Class CalculatePrimeCompletedEventArgs
Inherits AsyncCompletedEventArgs
Private numberToTestValue As Integer = 0
Private firstDivisorValue As Integer = 1
Private isPrimeValue As Boolean
Public Sub New( _
ByVal numberToTest As Integer, _
ByVal firstDivisor As Integer, _
ByVal isPrime As Boolean, _
ByVal e As Exception, _
ByVal canceled As Boolean, _
ByVal state As Object)
MyBase.New(e, canceled, state)
Me.numberToTestValue = numberToTest
Me.firstDivisorValue = firstDivisor
Me.isPrimeValue = isPrime
End Sub
Public ReadOnly Property NumberToTest() As Integer
Get
' Raise an exception if the operation failed
' or was canceled.
RaiseExceptionIfNecessary()
' If the operation was successful, return
' the property value.
Return numberToTestValue
End Get
End Property
Public ReadOnly Property FirstDivisor() As Integer
Get
' Raise an exception if the operation failed
' or was canceled.
RaiseExceptionIfNecessary()
' If the operation was successful, return
' the property value.
Return firstDivisorValue
End Get
End Property
Public ReadOnly Property IsPrime() As Boolean
Get
' Raise an exception if the operation failed
' or was canceled.
RaiseExceptionIfNecessary()
' If the operation was successful, return
' the property value.
Return isPrimeValue
End Get
End Property
End Class
using System;
using System.Collections;
using System.Collections.Specialized;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Globalization;
using System.Threading;
using System.Windows.Forms;
...
/////////////////////////////////////////////////////////////
#region PrimeNumberCalculator Implementation
public delegate void ProgressChangedEventHandler(
ProgressChangedEventArgs e);
public delegate void CalculatePrimeCompletedEventHandler(
object sender,
CalculatePrimeCompletedEventArgs e);
// This class implements the Event-based Asynchronous Pattern.
// It asynchronously computes whether a number is prime or
// composite (not prime).
public class PrimeNumberCalculator : Component
{
private delegate void WorkerEventHandler(
int numberToCheck,
AsyncOperation asyncOp);
private SendOrPostCallback onProgressReportDelegate;
private SendOrPostCallback onCompletedDelegate;
private HybridDictionary userStateToLifetime =
new HybridDictionary();
private System.ComponentModel.Container components = null;
/////////////////////////////////////////////////////////////
#region Public events
public event ProgressChangedEventHandler ProgressChanged;
public event CalculatePrimeCompletedEventHandler CalculatePrimeCompleted;
#endregion
/////////////////////////////////////////////////////////////
#region Construction and destruction
public PrimeNumberCalculator(IContainer container)
{
container.Add(this);
InitializeComponent();
InitializeDelegates();
}
public PrimeNumberCalculator()
{
InitializeComponent();
InitializeDelegates();
}
protected virtual void InitializeDelegates()
{
onProgressReportDelegate =
new SendOrPostCallback(ReportProgress);
onCompletedDelegate =
new SendOrPostCallback(CalculateCompleted);
}
protected override void Dispose(bool disposing)
{
if (disposing)
{
if (components != null)
{
components.Dispose();
}
}
base.Dispose(disposing);
}
#endregion // Construction and destruction
/////////////////////////////////////////////////////////////
///
#region Implementation
// This method starts an asynchronous calculation.
// First, it checks the supplied task ID for uniqueness.
// If taskId is unique, it creates a new WorkerEventHandler
// and calls its BeginInvoke method to start the calculation.
public virtual void CalculatePrimeAsync(
int numberToTest,
object taskId)
{
// Create an AsyncOperation for taskId.
AsyncOperation asyncOp =
AsyncOperationManager.CreateOperation(taskId);
// Multiple threads will access the task dictionary,
// so it must be locked to serialize access.
lock (userStateToLifetime.SyncRoot)
{
if (userStateToLifetime.Contains(taskId))
{
throw new ArgumentException(
"Task ID parameter must be unique",
"taskId");
}
userStateToLifetime[taskId] = asyncOp;
}
// Start the asynchronous operation.
WorkerEventHandler workerDelegate = new WorkerEventHandler(CalculateWorker);
workerDelegate.BeginInvoke(
numberToTest,
asyncOp,
null,
null);
}
// Utility method for determining if a
// task has been canceled.
private bool TaskCanceled(object taskId)
{
return( userStateToLifetime[taskId] == null );
}
// This method cancels a pending asynchronous operation.
public void CancelAsync(object taskId)
{
AsyncOperation asyncOp = userStateToLifetime[taskId] as AsyncOperation;
if (asyncOp != null)
{
lock (userStateToLifetime.SyncRoot)
{
userStateToLifetime.Remove(taskId);
}
}
}
// This method performs the actual prime number computation.
// It is executed on the worker thread.
private void CalculateWorker(
int numberToTest,
AsyncOperation asyncOp)
{
bool isPrime = false;
int firstDivisor = 1;
Exception e = null;
// Check that the task is still active.
// The operation may have been canceled before
// the thread was scheduled.
if (!TaskCanceled(asyncOp.UserSuppliedState))
{
try
{
// Find all the prime numbers up to
// the square root of numberToTest.
ArrayList primes = BuildPrimeNumberList(
numberToTest,
asyncOp);
// Now we have a list of primes less than
// numberToTest.
isPrime = IsPrime(
primes,
numberToTest,
out firstDivisor);
}
catch (Exception ex)
{
e = ex;
}
}
//CalculatePrimeState calcState = new CalculatePrimeState(
// numberToTest,
// firstDivisor,
// isPrime,
// e,
// TaskCanceled(asyncOp.UserSuppliedState),
// asyncOp);
//this.CompletionMethod(calcState);
this.CompletionMethod(
numberToTest,
firstDivisor,
isPrime,
e,
TaskCanceled(asyncOp.UserSuppliedState),
asyncOp);
//completionMethodDelegate(calcState);
}
// This method computes the list of prime numbers used by the
// IsPrime method.
private ArrayList BuildPrimeNumberList(
int numberToTest,
AsyncOperation asyncOp)
{
ProgressChangedEventArgs e = null;
ArrayList primes = new ArrayList();
int firstDivisor;
int n = 5;
// Add the first prime numbers.
primes.Add(2);
primes.Add(3);
// Do the work.
while (n < numberToTest &&
!TaskCanceled( asyncOp.UserSuppliedState ) )
{
if (IsPrime(primes, n, out firstDivisor))
{
// Report to the client that a prime was found.
e = new CalculatePrimeProgressChangedEventArgs(
n,
(int)((float)n / (float)numberToTest * 100),
asyncOp.UserSuppliedState);
asyncOp.Post(this.onProgressReportDelegate, e);
primes.Add(n);
// Yield the rest of this time slice.
Thread.Sleep(0);
}
// Skip even numbers.
n += 2;
}
return primes;
}
// This method tests n for primality against the list of
// prime numbers contained in the primes parameter.
private bool IsPrime(
ArrayList primes,
int n,
out int firstDivisor)
{
bool foundDivisor = false;
bool exceedsSquareRoot = false;
int i = 0;
int divisor = 0;
firstDivisor = 1;
// Stop the search if:
// there are no more primes in the list,
// there is a divisor of n in the list, or
// there is a prime that is larger than
// the square root of n.
while (
(i < primes.Count) &&
!foundDivisor &&
!exceedsSquareRoot)
{
// The divisor variable will be the smallest
// prime number not yet tried.
divisor = (int)primes[i++];
// Determine whether the divisor is greater
// than the square root of n.
if (divisor * divisor > n)
{
exceedsSquareRoot = true;
}
// Determine whether the divisor is a factor of n.
else if (n % divisor == 0)
{
firstDivisor = divisor;
foundDivisor = true;
}
}
return !foundDivisor;
}
// This method is invoked via the AsyncOperation object,
// so it is guaranteed to be executed on the correct thread.
private void CalculateCompleted(object operationState)
{
CalculatePrimeCompletedEventArgs e =
operationState as CalculatePrimeCompletedEventArgs;
OnCalculatePrimeCompleted(e);
}
// This method is invoked via the AsyncOperation object,
// so it is guaranteed to be executed on the correct thread.
private void ReportProgress(object state)
{
ProgressChangedEventArgs e =
state as ProgressChangedEventArgs;
OnProgressChanged(e);
}
protected void OnCalculatePrimeCompleted(
CalculatePrimeCompletedEventArgs e)
{
if (CalculatePrimeCompleted != null)
{
CalculatePrimeCompleted(this, e);
}
}
protected void OnProgressChanged(ProgressChangedEventArgs e)
{
if (ProgressChanged != null)
{
ProgressChanged(e);
}
}
// This is the method that the underlying, free-threaded
// asynchronous behavior will invoke. This will happen on
// an arbitrary thread.
private void CompletionMethod(
int numberToTest,
int firstDivisor,
bool isPrime,
Exception exception,
bool canceled,
AsyncOperation asyncOp )
{
// If the task was not previously canceled,
// remove the task from the lifetime collection.
if (!canceled)
{
lock (userStateToLifetime.SyncRoot)
{
userStateToLifetime.Remove(asyncOp.UserSuppliedState);
}
}
// Package the results of the operation in a
// CalculatePrimeCompletedEventArgs.
CalculatePrimeCompletedEventArgs e =
new CalculatePrimeCompletedEventArgs(
numberToTest,
firstDivisor,
isPrime,
exception,
canceled,
asyncOp.UserSuppliedState);
// End the task. The asyncOp object is responsible
// for marshaling the call.
asyncOp.PostOperationCompleted(onCompletedDelegate, e);
// Note that after the call to OperationCompleted,
// asyncOp is no longer usable, and any attempt to use it
// will cause an exception to be thrown.
}
#endregion
/////////////////////////////////////////////////////////////
#region Component Designer generated code
private void InitializeComponent()
{
components = new System.ComponentModel.Container();
}
#endregion
}
public class CalculatePrimeProgressChangedEventArgs :
ProgressChangedEventArgs
{
private int latestPrimeNumberValue = 1;
public CalculatePrimeProgressChangedEventArgs(
int latestPrime,
int progressPercentage,
object userToken) : base( progressPercentage, userToken )
{
this.latestPrimeNumberValue = latestPrime;
}
public int LatestPrimeNumber
{
get
{
return latestPrimeNumberValue;
}
}
}
public class CalculatePrimeCompletedEventArgs :
AsyncCompletedEventArgs
{
private int numberToTestValue = 0;
private int firstDivisorValue = 1;
private bool isPrimeValue;
public CalculatePrimeCompletedEventArgs(
int numberToTest,
int firstDivisor,
bool isPrime,
Exception e,
bool canceled,
object state) : base(e, canceled, state)
{
this.numberToTestValue = numberToTest;
this.firstDivisorValue = firstDivisor;
this.isPrimeValue = isPrime;
}
public int NumberToTest
{
get
{
// Raise an exception if the operation failed or
// was canceled.
RaiseExceptionIfNecessary();
// If the operation was successful, return the
// property value.
return numberToTestValue;
}
}
public int FirstDivisor
{
get
{
// Raise an exception if the operation failed or
// was canceled.
RaiseExceptionIfNecessary();
// If the operation was successful, return the
// property value.
return firstDivisorValue;
}
}
public bool IsPrime
{
get
{
// Raise an exception if the operation failed or
// was canceled.
RaiseExceptionIfNecessary();
// If the operation was successful, return the
// property value.
return isPrimeValue;
}
}
}
#endregion
import System.*;
import System.Collections.*;
import System.Collections.Specialized.*;
import System.ComponentModel.*;
import System.Data.*;
import System.Drawing.*;
import System.Threading.*;
import System.Windows.Forms.*;