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C# How to cancel a Task.Run that is executing.

C# How to cancel a Task.Run that is executing.

(17 hits)
Overview: Hits=15 The cancallation token stop one or all threads from executing. Each Task.Run can have a global cancellation token passed as a parameter. In the following example, three threads are created to produce a list of numbers for squared, cubed, and quadric numbers. The threads are launched sychronously or non blocked threads and the ui waits all the threads to complete. Each thread block is processed by a ContinueWith lambda function. The lambda function checks if the result set has been canceled before proceeding. The thread tasks for each of the tasks checks if the thread has been cancelled. If the task has been cancel than it does not need to wait for thread completion.

https://johnbadams.wordpress.com/2012/03/10/understanding-cancellationtokensource-with-tasks/

CancellationTokenSource




CancellationTokenSource cancellationTokenSource = null;

        private IList<IEntity> Task1()
        {
            IList<IEntity> entityCollection = new List<IEntity>();
            for (int i = 0; i < 100; i++)
            {
                SquareNumber squareNumber = new SquareNumber();
                squareNumber.Value = System.Math.Pow((double)i, 2.0);
                entityCollection.Add(squareNumber);
                Thread.Sleep(50);
            }
            return entityCollection;
        }
        private IList<IEntity> Task2()
        {
            IList<IEntity> entityCollection = new List<IEntity>();
            for (int i = 0; i < 100; i++)
            {
                CubeNumber cubeNumber = new CubeNumber();
                cubeNumber.Value = System.Math.Pow((double)i, 3.0);
                entityCollection.Add(cubeNumber);
                Thread.Sleep(50);
            }
            return entityCollection;
        }
        private IList<IEntity> Task3()
        {
            IList<IEntity> entityCollection = new List<IEntity>();

            //2x2 – 4x – 3 = 0 baseline
            Quadraic quadraic = new Quadraic(2.0,-4.0,-3.0);
            entityCollection.Add(quadraic);

            for (float i = 1.0f; i < 3.0f; i += 1.0f )
            {
                for (float j = -2.0f; j < 2.0f; j += 1.0f)
                {
                    for (float k = -2.0f; k < 2.0f; k += 1.0f)
                    {
                        quadraic = new Quadraic(i,j,k);
                        entityCollection.Add(quadraic);
                        Thread.Sleep(50);
                    }
                }

            }

            return entityCollection;
        }

Task.ContinueWith - Unit Test

        [Fact]
        public void TestContinueWith()
        {
            cancellationTokenSource = new CancellationTokenSource();
	    //uncomment to see how the cancellationToken works
            //cancellationTokenSource.Cancel();
            Task<IList<IEntity>> listEntities1Task = Task.Run(async () => Task1(), cancellationTokenSource.Token);
            Task<IList<IEntity>> listEntities2Task = Task.Run(async () => Task2(), cancellationTokenSource.Token);
            Task<IList<IEntity>> listEntities3Task = Task.Run(async () => Task3(), cancellationTokenSource.Token);

            Task continueTask = listEntities1Task.ContinueWith(
                query => 
                {
                    if (query.IsCanceled == false)
                    {
                        foreach (SquareNumber item in query.Result)
                        {
                            output.WriteLine($"Task 1: {item.Value}");
                        }
                    }
                });

            Task continueTask2 = listEntities2Task.ContinueWith(
                query =>
                {
                    if (query.IsCanceled == false)
                    {
                        foreach (CubeNumber item in query.Result)
                        {
                            output.WriteLine($"Task 2: {item.Value}");
                        }
                    }
                });
            Task continueTask3 = listEntities3Task.ContinueWith(
                 query =>
                 {
                     if (query.IsCanceled == false)
                     {
                         foreach (Quadraic item in query.Result)
                         {
                             output.WriteLine($"Task 3: X1={item.X1} X2={item.X2}");
                         }
                     }
                 });

            if (listEntities1Task.IsCanceled==false && listEntities2Task.IsCanceled == false && listEntities3Task.IsCanceled == false)
            Task.WaitAll(listEntities1Task, listEntities2Task, listEntities3Task);

        }

IEntity : SquareNumber, CubeNumber, Quadraic

    public interface IEntity { }
    public class SquareNumber:IEntity {
        public double Value { get; set; }
    }
    public class CubeNumber : IEntity {
        public double Value { get; set; }
    }
    public class Quadraic : IEntity {

        public Quadraic(double A, double B, double C)
        {
            this.A = A;
            this.B = B;
            this.C = C;

            this.X1 = (
                 (-1)*B + System.Math.Sqrt(
                (B * B)-(4.0 * A * C)
                )
                ) 
                / (2.0 * A);

            this.X2 = (
                (-1) * B - System.Math.Sqrt(
                (B * B) - (4.0 * A * C)
                )
                )
                / (2.0 * A);

        }
        public double A { get; set; }
        public double B { get; set; }
        public double C { get; set; }
        public double X1 { get; set; }
        public double X2 { get; set; }
     
    }
....

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