HOW TO：使用執行緒集區 (C# 和 Visual Basic)

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02/28/2013

「執行緒共用」(Thread Pooling) 是一種多執行緒的形式，當建立執行緒時，其中的工作會加入佇列並自動啟動。如需詳細資訊，請參閱執行緒集區 (C# 和 Visual Basic)。

下列範例使用 .NET Framework 執行緒集區，計算介於 20 到 40 間十個數字的 Fibonacci 結果。每個 Fibonacci 結果都會以 Fibonacci 類別代表，此類別提供名為 ThreadPoolCallback 且會執行計算的方法。這時會建立表示每個 Fibonacci 值的物件，而且 ThreadPoolCallback 方法會傳遞到 QueueUserWorkItem，這個多載會指派集區中的可用執行緒來執行方法。

因為提供了半隨機值給每個 Fibonacci 物件計算，而且其中每個執行緒都會競爭處理器時間，所以您無法預先知道要花多少時間，才能計算完所有十個結果。這就是在建構期間，ManualResetEvent 類別的執行個體 (Instance) 會傳遞給每個 Fibonacci 物件的原因。每個物件完成計算時，都會傳送所提供事件物件的信號，這樣可讓主要執行緒使用 WaitAll 阻斷執行，直到十個 Fibonacci 物件都計算出結果為止。然後 Main 方法會顯示每個 Fibonacci 結果。

範例

Imports System.Threading

Module Module1

    Public Class Fibonacci
        Private _n As Integer
        Private _fibOfN
        Private _doneEvent As ManualResetEvent

        Public ReadOnly Property N() As Integer
            Get
                Return _n
            End Get
        End Property

        Public ReadOnly Property FibOfN() As Integer
            Get
                Return _fibOfN
            End Get
        End Property

        Sub New(ByVal n As Integer, ByVal doneEvent As ManualResetEvent)
            _n = n
            _doneEvent = doneEvent
        End Sub

        ' Wrapper method for use with the thread pool.
        Public Sub ThreadPoolCallBack(ByVal threadContext As Object)
            Dim threadIndex As Integer = CType(threadContext, Integer)
            Console.WriteLine("thread {0} started...", threadIndex)
            _fibOfN = Calculate(_n)
            Console.WriteLine("thread {0} result calculated...", threadIndex)
            _doneEvent.Set()
        End Sub

        Public Function Calculate(ByVal n As Integer) As Integer
            If n <= 1 Then
                Return n
            End If
            Return Calculate(n - 1) + Calculate(n - 2)
        End Function

    End Class


    <MTAThread()> 
    Sub Main()
        Const FibonacciCalculations As Integer = 9 ' 0 to 9

        ' One event is used for each Fibonacci object
        Dim doneEvents(FibonacciCalculations) As ManualResetEvent
        Dim fibArray(FibonacciCalculations) As Fibonacci
        Dim r As New Random()

        ' Configure and start threads using ThreadPool.
        Console.WriteLine("launching {0} tasks...", FibonacciCalculations)

        For i As Integer = 0 To FibonacciCalculations
            doneEvents(i) = New ManualResetEvent(False)
            Dim f = New Fibonacci(r.Next(20, 40), doneEvents(i))
            fibArray(i) = f
            ThreadPool.QueueUserWorkItem(AddressOf f.ThreadPoolCallBack, i)
        Next

        ' Wait for all threads in pool to calculate.
        WaitHandle.WaitAll(doneEvents)
        Console.WriteLine("All calculations are complete.")

        ' Display the results.
        For i As Integer = 0 To FibonacciCalculations
            Dim f As Fibonacci = fibArray(i)
            Console.WriteLine("Fibonacci({0}) = {1}", f.N, f.FibOfN)
        Next
    End Sub

End Module

using System;
using System.Threading;

public class Fibonacci
{
    private int _n;
    private int _fibOfN;
    private ManualResetEvent _doneEvent;

    public int N { get { return _n; } }
    public int FibOfN { get { return _fibOfN; } }

    // Constructor.
    public Fibonacci(int n, ManualResetEvent doneEvent)
    {
        _n = n;
        _doneEvent = doneEvent;
    }

    // Wrapper method for use with thread pool.
    public void ThreadPoolCallback(Object threadContext)
    {
        int threadIndex = (int)threadContext;
        Console.WriteLine("thread {0} started...", threadIndex);
        _fibOfN = Calculate(_n);
        Console.WriteLine("thread {0} result calculated...", threadIndex);
        _doneEvent.Set();
    }

    // Recursive method that calculates the Nth Fibonacci number.
    public int Calculate(int n)
    {
        if (n <= 1)
        {
            return n;
        }

        return Calculate(n - 1) + Calculate(n - 2);
    }
}

public class ThreadPoolExample
{
    static void Main()
    {
        const int FibonacciCalculations = 10;

        // One event is used for each Fibonacci object.
        ManualResetEvent[] doneEvents = new ManualResetEvent[FibonacciCalculations];
        Fibonacci[] fibArray = new Fibonacci[FibonacciCalculations];
        Random r = new Random();

        // Configure and start threads using ThreadPool.
        Console.WriteLine("launching {0} tasks...", FibonacciCalculations);
        for (int i = 0; i < FibonacciCalculations; i++)
        {
            doneEvents[i] = new ManualResetEvent(false);
            Fibonacci f = new Fibonacci(r.Next(20, 40), doneEvents[i]);
            fibArray[i] = f;
            ThreadPool.QueueUserWorkItem(f.ThreadPoolCallback, i);
        }

        // Wait for all threads in pool to calculate.
        WaitHandle.WaitAll(doneEvents);
        Console.WriteLine("All calculations are complete.");

        // Display the results.
        for (int i= 0; i<FibonacciCalculations; i++)
        {
            Fibonacci f = fibArray[i];
            Console.WriteLine("Fibonacci({0}) = {1}", f.N, f.FibOfN);
        }
    }
}

下列是輸出的範例。

launching 10 tasks...
thread 0 started...
thread 1 started...
thread 1 result calculated...
thread 2 started...
thread 2 result calculated...
thread 3 started...
thread 3 result calculated...
thread 4 started...
thread 0 result calculated...
thread 5 started...
thread 5 result calculated...
thread 6 started...
thread 4 result calculated...
thread 7 started...
thread 6 result calculated...
thread 8 started...
thread 8 result calculated...
thread 9 started...
thread 9 result calculated...
thread 7 result calculated...
All calculations are complete.
Fibonacci(38) = 39088169
Fibonacci(29) = 514229
Fibonacci(25) = 75025
Fibonacci(22) = 17711
Fibonacci(38) = 39088169
Fibonacci(29) = 514229
Fibonacci(29) = 514229
Fibonacci(38) = 39088169
Fibonacci(21) = 10946
Fibonacci(27) = 196418

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HOW TO：使用執行緒集區 (C# 和 Visual Basic)

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