Why await Task.Run( () => SomeMethod() ) doesn't wait?

Asked Jul 20 '17 at 20:10

Active Jul 20 '17 at 20:16

Viewed 119 times

I tried to read Cleary's post and also googled around StackOverflow, but still doesn't get some behavior regarding async await vs await Task.Run()

My Code:

private async void ValidateLexisNexis()
    {
        _view.LogProcess(@"I'm Starting..", true);
        await Task.Run(() => SomeAsynchMethod());
        _view.LogProcess(@"Im out of SomeSynchMethod", true);
    }
private async void SomeAsynchMethod()
    {
        await Task.Delay(2000);
        MessageBox.Show(@"Hi I'm in");
    }

Now I expected:

Log I'm Starting...
Create a new thread and run SomeAsynchMethod(), wait for the response, Message "Hi I'm In"
Log I'm out of someAsynchMethod

Now, no 2 is my problem, the code continue to no 3 before finishing no 2, and I wonder, what's the purpose of the await before Task.Run ?? shouldn't the ValidateLexisNexis wait for the response if await Task.Run before continue to log I'm out??

P.S. - I know I can just use await SomeAsynchMehtod() without Task.Run and then it works as expected, but I'm trying to understand why with Task.Run the await doesn't really wait.

Thanks!!!!

asked Jul 20 '17 at 20:10

Roni Axelrad

1

You must never use `async void`. – SLaks Jul 20 '17 at 20:11
`I know I can just use await SomeAsynchMehtod() without Task.Run` Can you though? – Servy Jul 20 '17 at 20:11
@SLaks Except in all of the cases where it's appropriate... – Servy Jul 20 '17 at 20:12
1

@Servy There is only one case where its appropriate as far as I know (event handlers) – maccettura Jul 20 '17 at 20:12
@maccettura That's the most common case, not the only case. – Servy Jul 20 '17 at 20:13
Why not just `await SomeAsynchMethod()`? – Dai Jul 20 '17 at 20:13
@Dai Try it and see for yourself. – Servy Jul 20 '17 at 20:13
So that's because I return void and not Task ? – Roni Axelrad Jul 20 '17 at 20:15
1

OP, try your code like [this](https://pastebin.com/7DwXmv2z) – maccettura Jul 20 '17 at 20:16
3

Change `await Task.Run(() => SomeAsynchMethod());` to `await Task.Run(async () => await SomeAsynchMethod());`. Or better just `await SomeAsynchMethod()`. And use `Task` as return type. – NtFreX Jul 20 '17 at 20:16
Also learned from Stephen Cleary: never, ever use anything else than `Task` or `Task` as return value from an async function, with the one and only exception the event handler where no one is waiting for the result. Your compiler probably have warned you for this – Harald Coppoolse Jul 21 '17 at 06:33

Why await Task.Run( () => SomeMethod() ) doesn't wait?

0 Answers0