How can I assign a name to a task in TPL

Question

I'm going to use lots of tasks running on my application. Each bunch of tasks is running for some reason. I would like to name these tasks so when I watch the Parallel Tasks window, I could recognize them easily.

With another point of view, consider I'm using tasks at the framework level to populate a list. A developer that use my framework is also using tasks for her job. If she looks at the Parallel Tasks Window she will find some tasks having no idea about. I want to name tasks so she can distinguish the framework tasks from her tasks.

It would be very convenient if there was such API:

var task = new Task(action, "Growth calculation task")

or maybe:

var task = Task.Factory.StartNew(action, "Populating the datagrid")

or even while working with Parallel.ForEach

Parallel.ForEach(list, action, "Salary Calculation Task"

Is it possible to name a task?

Is it possible to give ‍‍‍Parallel.ForEach a naming structure (maybe using a lambda) so it creates tasks with that naming?

Is there such API somewhere that I'm missing?

---

I've also tried to use an inherited task to override it's ToString(). But unfortunately the Parallel Tasks window doesn't use ToString()!

class NamedTask : Task
{
    private string TaskName { get; set; }
    public NamedTask(Action action, string taskName):base(action)
    {
        TaskName = taskName;
    }

    public override string ToString()
    {
        return TaskName;
    }
}

Solution 1

You can't really name a Task, but you can name the method which is executed by a Task, which is then shown in the Parallel Tasks windows. So, if naming the Tasks is important for you, don't use lambdas, use normal named methods.

Surprisingly, this works even with Parallel, even though there the Task isn't executing your method directly. I think this is because Parallel Tasks somehow knows about Tasks from Parallel and handles them differently.

Solution 2

You could relate any object with any object. Here is an extension for Task. It uses a WeakReference so the task can still be garbage collected when all references are out of scope.

Usage:

var myTask = new Task(...
myTask.Tag("The name here");
var nameOfTask = (string)myTask.Tag();

Extension class:

public static class TaskExtensions
{
    private static readonly Dictionary<WeakReference<Task>, object> TaskNames = new Dictionary<WeakReference<Task>, object>(); 

    public static void Tag(this Task pTask, object pTag)
    {
        if (pTask == null) return;
        var weakReference = ContainsTask(pTask);
        if (weakReference == null)
        {
            weakReference = new WeakReference<Task>(pTask);
        }
        TaskNames[weakReference] = pTag;
    }

    public static object Tag(this Task pTask)
    {
        var weakReference = ContainsTask(pTask);
        if (weakReference == null) return null;
        return TaskNames[weakReference];
    }

    private static WeakReference<Task> ContainsTask(Task pTask)
    {
        foreach (var kvp in TaskNames.ToList())
        {
            var weakReference = kvp.Key;

            Task taskFromReference;
            if (!weakReference.TryGetTarget(out taskFromReference))
            {
                TaskNames.Remove(weakReference); //Keep the dictionary clean.
                continue;
            }

            if (pTask == taskFromReference)
            {
                return weakReference;
            }
        }
        return null;
    }
}

Solution 3

You can't name tasks.

The task library is internally using a thread pool, so the threads can't be named. Also your inheritance approach won't work, because methods like ".ContinueWith()" will always create a new task, which won't inherit from your class.

Solution 4

If you only need to know the name of the task after the task is finished then you could just pass it as a parameter. Return it as a part of the task result.

    private async Task<string[]> MyTask(int x, string taskName)
    {
        return new[]
        {
            taskName, x.ToString()
        };
    }

Or map your tasks to a dictionary

        var mapping = new Dictionary<Task, string>();
        var task = new Task(() => Console.WriteLine("myNullTask"));
        mapping.Add(task, "myNullTask");
        foreach (var taskX in mapping)
        {
            Console.WriteLine(
                $"Task Id: {taskX.Key.Id}, " +
                $"Task Name: {taskX.Value}, " +
                $"Task Status: {taskX.Key.Status}");
        }

Solution 5

I dont think you can name the tasks. You can use Task.Id to track the tasks.

View more solutions

Comments

[mehrandvd]

Currently I don't need ContinueWith() to continue with a task of my type NamedTask. I just want my task to have a name. I know Tasks use threads internally, but what should make us not to name a task? It seems logical tasks to have a name.

[mehrandvd]

Thanks. Nice attribute. It may help, I'll check it. But the question remains. Is tasks something that can't have a name? why?

[JustAnotherUserYouMayKnow]

Because it's not logical for tasks to have a name. Tasks are used for short async operations, not for long requests.

[Adrian Zanescu]

that is nice but in the very often case when you have multiple tasks executing the same method this is not very helpful anyway

[mehrandvd]

It's a good solution, and a practical one. Thanks. But It was better to create names. for example, calculation of person A, calculation of person B, ... A parametric naming would be better... But my fundamental question is that why isn't there a simple name property on the tasks there!

[mehrandvd]

I've checked the attribute. The Parallel Tasks window doesn't use it. Besides we could override the ToString() instead of using this attribute.

[Arvind Kumar Chaodhary]

Use these above two classes like following -NamedTaskSchedular.RunNamedTask( "1", Program.Act1); public static void Act1(){}

[Mike de Klerk]

@mehrandvd I think this should be the accepted answer :)

[Chris]

really like this one, but why not use ConcurrentDictionary?

[Mike de Klerk]

@Harry I think it depends on how the Tasks are tagged. Is that done in an async process? If that is the case then using a lock or ConcurrentDictionary is needed indeed. In my experience, tasks are not created (and thus Tagged/named) in async code by default.

[Theodor Zoulias]

There is already a built-in TaskFactory class. Creating a class with the same name that does something different could cause confusion.

[Kees van Zon]

Thanks for pointing that out Theodor; I changed the class name to avoid confusion.

[Dmitry Streblechenko]

It might also make sense for Tag() to return Task rather than void - this way you can chain the calls.