What is the difference between Task.Run() and await Task.Run()?

Question

Following program is designed using general Task.Run() and using async and await (asynchronous). In both cases a different Thread is taken from Thread pool for new task. So, what is the difference? Asynchronous means it should use the main thread and free it until task completed. But it is also using another thread rather than using main thread.

public class Worker2
{
    public bool IsComplete { get; private set; }
    internal void DoWork()
    {
        this.IsComplete = false;
        Console.WriteLine("Doing Work.");
        Task.Run(new Action(LongOperation));
        Console.WriteLine("Work Completed");
        IsComplete = true;
    }

    private void LongOperation()
    {
            Console.WriteLine("long operation thread thread :" + Thread.CurrentThread.ManagedThreadId);//Thread Id = 7. it is different from main thread id.
            Console.WriteLine("Working!");
            Thread.Sleep(3000);
    }
}

//And asynchronous

public class Worker2
{
    public bool IsComplete { get; private set; }
    internal async void DoWork()
    {
        this.IsComplete = false;
        Console.WriteLine("Doing Work.");       
        await LongOperation();
        Console.WriteLine("Work Completed");
        IsComplete = true;
    }

    private Task LongOperation()
    {

        return Task.Run(() =>
            {
                Console.WriteLine("long operation thread thread :" + Thread.CurrentThread.ManagedThreadId);
                Console.WriteLine("Working!");
                Thread.Sleep(3000);
            });
    }
}

Answer 1

What is the difference between Task.Run() and await Task.Run()?

The first starts a task and then does the work immediately after that task, before the task completes.

The second starts a task and then does different work until the task is completed, at which point it does the work after the task.

Let's make an analogy. Your first program is like doing this:

• Hire someone to mow the lawn.
• Tell your spouse the lawn is mowed.
• Go watch Netflix.

Your second program is:

• Hire someone to mow the lawn.
• Watch Netflix while the lawn is being mowed.
• When the lawn is done being mowed and the movie is over, tell spouse the lawn is mowed.

Clearly those are very different workflows. Both are asynchronous, but only the latter has an asynchronous wait in it. We asynchronously wait to tell the spouse that the lawn is mowed until it actually is mowed.