如何：使用平行任務周遊二元樹

下列範例示範兩種使用平行任務來遍歷樹狀結構的方法。 創造樹本身的過程留作練習。

範例

public class TreeWalk
{
    static void Main()
    {
        Tree<MyClass> tree = new Tree<MyClass>();

        // ...populate tree (left as an exercise)

        // Define the Action to perform on each node.
        Action<MyClass> myAction = x => Console.WriteLine($"{x.Name} : {x.Number}");

        // Traverse the tree with parallel tasks.
        DoTree(tree, myAction);
    }

    public class MyClass
    {
        public string Name { get; set; }
        public int Number { get; set; }
    }
    public class Tree<T>
    {
        public Tree<T> Left;
        public Tree<T> Right;
        public T Data;
    }

    // By using tasks explicitly.
    public static void DoTree<T>(Tree<T> tree, Action<T> action)
    {
        if (tree == null) return;
        var left = Task.Factory.StartNew(() => DoTree(tree.Left, action));
        var right = Task.Factory.StartNew(() => DoTree(tree.Right, action));
        action(tree.Data);

        try
        {
            Task.WaitAll(left, right);
        }
        catch (AggregateException)
        {
            //handle exceptions here
        }
    }

    // By using Parallel.Invoke
    public static void DoTree2<T>(Tree<T> tree, Action<T> action)
    {
        if (tree == null) return;
        Parallel.Invoke(
            () => DoTree2(tree.Left, action),
            () => DoTree2(tree.Right, action),
            () => action(tree.Data)
        );
    }
}

Imports System.Threading.Tasks

Public Class TreeWalk

    Shared Sub Main()

        Dim tree As Tree(Of Person) = New Tree(Of Person)()

        ' ...populate tree (left as an exercise)

        ' Define the Action to perform on each node.
        Dim myAction As Action(Of Person) = New Action(Of Person)(Sub(x)
                                                                      Console.WriteLine("{0}  : {1} ", x.Name, x.Number)
                                                                  End Sub)

        ' Traverse the tree with parallel tasks.
        DoTree(tree, myAction)
    End Sub

    Public Class Person
        Public Name As String
        Public Number As Integer
    End Class

    Public Class Tree(Of T)
        Public Left As Tree(Of T)
        Public Right As Tree(Of T)
        Public Data As T
    End Class

    ' By using tasks explicitly.
    Public Shared Sub DoTree(Of T)(ByVal myTree As Tree(Of T), ByVal a As Action(Of T))
        If myTree Is Nothing Then
            Return
        End If
        Dim left = Task.Factory.StartNew(Sub() DoTree(myTree.Left, a))
        Dim right = Task.Factory.StartNew(Sub() DoTree(myTree.Right, a))
        a(myTree.Data)

        Try
            Task.WaitAll(left, right)
        Catch ae As AggregateException
            'handle exceptions here
        End Try
    End Sub

    ' By using Parallel.Invoke
    Public Shared Sub DoTree2(Of T)(ByVal myTree As Tree(Of T), ByVal myAct As Action(Of T))
        If myTree Is Nothing Then
            Return
        End If
        Parallel.Invoke(
            Sub() DoTree2(myTree.Left, myAct),
            Sub() DoTree2(myTree.Right, myAct),
            Sub() myAct(myTree.Data)
        )
    End Sub
End Class

顯示的兩種方法在功能上是相等的。 藉由使用 StartNew 方法來建立及執行任務，您可以取得可用來等候任務及處理例外狀況的控制物件。

另請參閱

• 任務平行程式庫 (TPL)