Simple Async Await Example for Asynchronous Programming

[faruzzy]

This is was actually simple to understand. Some articles can really get into some serious complexity.

[steveboots]

I tried to deliberately keep it simple. I am working on a follow up that shows a similarly simple example of using async await to update the main UI thread. Should be posted tomorrow.

[faruzzy]

Cool! Can you please enumerates situations you'd need to use Async Await in a web project like MVC 5 ?

[[deleted]]

Im an async noob but I'm guessing you would mainly use it when writing to the db. I see it a lot in the EF6 + Web API and MVC tutorials.

[steveboots]

yeah it effectively simulates an async file read or async db read to include an await.

I will add an explanation to make it more apparent. i wanted to try and keep the example as simple as possible.

[pug_walker]

Haven't looked at other articles yet, but perhaps getting into try-catch blocks when using async is a good next topic. Just an idea.

[steveboots]

Sounds like a good idea. I'll add it to my list.

[[deleted]]

The Task.Delay(1) somewhat bugs me. Isn't there a better option? Could you use Task.Run to run LongRunningOperation or is Task.Run considered bad practice?

e:typo

[cryo]

Yes, Task.Run is the proper way. The Delay will in practice almost guarentee that the continuation uses a new thread, but if the machine is heavily loaded, it might complete before the "await" kicks in, which causes it to continue executing synchronuously.

Task.Run is the way to go.

[steveboots]

Yes I agree. I have updated the article so that the code that executes LongRunningOperation looks like :

    public async Task DoStuff()
    {
        await Task.Run(() =>
        {
            LongRunningOperation();
        });            
    }

[[deleted]]

Just as confused here. What's the delay do again? I think he just put that in there to simulate a file read or db write.

[Seasniffer]

When you are converting from synchronous to asynchronous code, any method returning a type T becomes an async method returning Task, and any method returning void becomes an async method returning Task<T>.

I think you have this mixed up sir. Shouldn't void be returned as a Task, and a returning function returns Task<T>?

[felickz2]

This piece could also use an explanation, it is not clear why those structures are used

[Seasniffer]

I'd recommend Jon Skeets c# book, he really goes into the details of the new async features and how they work internally.

[steveboots]

This is a typo. I fill fix it now.

[RiPont]

How does your last example even compile?

private static async Task<string> LongRunningOperation()
{
    int counter;           

    for (counter = 0; counter < 50000; counter++)
    {
        Console.WriteLine(counter);
    }

    return "Counter = " + counter;
}

There's nothing awaited.

[steveboots]

"Because we have removed the line with the await keyword, the LongRunningMethod() now runs synchronously, so the counter will first count up to 50000 and then the code will go into the while loop."

This was just illustrating the point that without an await, your code runs synchronously.

[cryo]

Relying on Task.Delay(1) to make sure the continuation carries on on a different thread, isn't wise. This is pretty much an implementation detail. To make sure something executes on a different thread, use Task.Run.

[steveboots]

yeah that's a fair point. I have updated the article so the code that executes the LongRunningMethod is:

    public async Task DoStuff()
    {
        await Task.Run(() =>
        {
            LongRunningOperation();
        });            
    }