方法: 並列タスクでバイナリ ツリーを走査する

次の例は、ツリーのデータ構造を走査する場合の並列タスクを 2 とおり示しています。 ツリーの作成は演習として残されています。

使用例

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 Not 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 Not myTree Is Nothing Then
            Return
        End If
        Parallel.Invoke(
            Sub() DoTree2(myTree.Left, myAct),
            Sub() DoTree2(myTree.Left, myAct),
            Sub() myAct(myTree.Data)
        )
    End Sub

End Class

    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("{0} : {1}", 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 explcitly.
        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)
            );
        }

    }

2 つのメソッドは機能的に同じです。 StartNew() メソッドを使用してタスクを作成および実行し、タスクでの待機や例外処理に使用できるタスクからハンドルを取得します。

参照

概念

タスク並列ライブラリ