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How to: Implement a Component That Supports the Event-based Asynchronous Pattern

The following code example implements a component with an asynchronous method, according to the Event-based Asynchronous Pattern Overview. The component is a prime number calculator that uses the Sieve of Eratosthenes algorithm to determine if a number is prime or composite.

There is extensive support for this task in Visual Studio. Walkthrough: Implementing a Component That Supports the Event-based Asynchronous Pattern
Walkthrough: Implementing a Component That Supports the Event-based Asynchronous Pattern
Walkthrough: Implementing a Component That Supports the Event-based Asynchronous Pattern
Walkthrough: Implementing a Component That Supports the Event-based Asynchronous Pattern
Walkthrough: Implementing a Component That Supports the Event-based Asynchronous Pattern

For an example client that uses the PrimeNumberCalculator component, see How to: Implement a Client of the Event-based Asynchronous Pattern.

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
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