Where and how to place await keyword

Question

I'm trying to understand how asynchronous works. This is my code:

class Program
{
    static void Main(string[] args)
    {
        Task<string> strReturned = returnStringAsync();
        Console.WriteLine("hello!");
        string name = await strReturned; //error: The 'await' operator can only be used 
                                         //within an async method. Consider marking this 
                                         //method with the 'async' modifier and changing 
                                         //its return type to 'Task'

        Console.WriteLine(name);
    }

    static async Task<string> returnStringAsync()
    {
        Thread.Sleep(5000);
        return "Richard"; 
    }
}

Any thing wrong?

I saw that, but the error message explains very well what is wrong with what you tried. So what did you not get? — poke, Jan 06 '14 at 02:23
In an `async` method, you should use [`await Task.Delay(5000)`](http://msdn.microsoft.com/en-us/library/hh194873.aspx) instead of `Thread.Sleep(5000)`. — Sam Harwell, Jan 06 '14 at 02:28
check http://stackoverflow.com/questions/14658001/cannot-implicitly-convert-type-string-to-system-threading-tasks-taskstring — techBeginner, Jan 06 '14 at 02:29
Two things I see that are wrong. First, if you added the async keyword to the main method, it might even compile, but what do you expect it to do? When it hits the await keyword the whole method will unwind and the program will end. What are you trying to do? — Phillip Scott Givens, Jan 06 '14 at 02:34
@280Z28, replacing Thread.Sleep with await Task.Delay solved the problem. — Richard77, Jan 06 '14 at 02:36
@Richard77: You may find my [async/await intro](http://blog.stephencleary.com/2012/02/async-and-await.html) helpful. — Stephen Cleary, Jan 06 '14 at 12:43

score 1 · Answer 1 · answered Jan 06 '14 at 02:39

1

This works

class Program
{
    static void Main(string[] args)
    {
        Task<string> str = returnStringAsync();
        Console.WriteLine("hello!");

        string name = str.Result;

        Console.WriteLine(name);
    }

    static async Task<string> returnStringAsync()
    {
        await Task.Delay(5000);
        return "Richard"; 
    }
}

answered Jan 06 '14 at 02:39

Richard77

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Yes, this works, but it's pretty much the only case where it's a good idea to call `Result` (or `Wait()`) on an `async` `Task`. In most other cases, doing that would cause a deadlock. – svick Jan 06 '14 at 10:43
@svick. Then give a better way to write this code. In fact, this is the very first time I've even written a code on async and await. Everything is still new to me in that field. – Richard77 Jan 06 '14 at 23:05
In this specific case (console application running `async` code), using `Result` *is* the right way. But in most other cases, it's not. – svick Jan 07 '14 at 01:43

Where and how to place await keyword

1 Answers1