I want to create three tasks a,b,c and run in order a,b,c using task chaining by using Task.continueWith

Question

I want to create three tasks a,b,c and run in order a,b,c using task chaining by using Task.continueWith

Vishal2 Bansal 265

Following is the code block:-

		public static async Task task1()
         {
            await Task.Delay(4000);
             Console.WriteLine("Task 1 completed");
             
         }
        public static async Task task2()
        {
            await Task.Delay(1000);
            
                Console.WriteLine("Task 2 completed");
        }
        public static async Task task3()
        {
            await Task.Delay(2000);
            
                Console.WriteLine("Task 3 completed");
            
        }
        static void Main(string[] args)
        {
            Task t = Task.Run(() => { });
            t = t.ContinueWith(t =>
            {
                task1();
            });
            t = t.ContinueWith(t =>
            {
                task2();
            });
            t = t.ContinueWith(t =>
            {
                task3();
            });
            Console.ReadLine();
        }

Current Output of Above Code:-

Task 2 completed
Task 3 completed
Task 1 completed

Expected Output(what i want) :-

Task 1 completed
Task 2 completed
Task 3 completed

Please help and point out any mistake if i am doing...

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Answer 1

Hi @Vishal2 Bansal , Welcome to Microsoft Q&A,

You call each task in the ContinueWith method, but you don't use await to wait for those tasks to complete. Therefore, the tasks are executed concurrently, causing the output to be in a different order than you expect.

You could try the following code to get what you wanted.

static void Main(string[] args)
{
    Task t = Task.Run(() => { });

    t = t.ContinueWith(_ =>
    {
        return Task1();
    }).Unwrap();

    t = t.ContinueWith(_ =>
    {
        return Task2();
    }).Unwrap();

    t = t.ContinueWith(_ =>
    {
        return Task3();
    }).Unwrap();

    t.Wait(); 

    Console.ReadLine();
}

Use the ContinueWith method to ensure that each task starts executing after the previous task completes. Use the Unwrap method to flatten nested tasks (since ContinueWith returns a Task<Task>). Finally, call the Wait method to wait for all tasks to complete.

Or

 static async Task Main(string[] args)
    {
        await Task1();
        await Task2();
        await Task3();
        Console.ReadLine();
    }

Best Regards,

Jiale

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Vishal2 Bansal 265 Reputation points

2024-02-09T11:06:29.79+00:00

Thank you @Anonymous . But I have one more query i don't want to create different task variables. I only want to maintain one or i can you task array. But i have some doubts. a) If I use one task variable then how to assign other tasks to this variable while previous tasks are pending. b) I i use task array to insert tasks in it. Then according to my program i have multiple tasks which are generated at variable times each must be finished after previous other tasks are finished. Then my task array size will increase with time and my performance of program reduced drastically by using taskArray.waitAll(). So how to flush off completed tasks from the array.?

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I want to create three tasks a,b,c and run in order a,b,c using task chaining by using Task.continueWith

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