Cómo: Recorrer un árbol binario con tareas paralelas
En el siguiente ejemplo se muestran dos maneras de usar tareas paralelas para atravesar una estructura de datos en árbol. La creación del propio árbol se deja como ejercicio.
Ejemplo
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)
);
}
}
Los dos métodos mostrados son equivalentes desde el punto de vista funcional. Cuando se usa el método StartNew() para crear y ejecutar las tareas, estas devuelven un identificador que se puede usar para esperar en ellas y controlar las excepciones.