C# async, await

Question

I have simple code which I want to be executed asynchrounously:

public async Task EncryptAsync()
{
    for (int i = 0; i < 10; i++)
    {
        // shift bytes
        // column multiplication
        // and so on
    }
}

That is the way I call above method:

private async void Encryption()
{
    ShowBusyIndicator();

    await encryptor.EncryptAsync();

    HideBusyIndicator();
}

The point is, when I add await Task.Delay(1000); in this method, busi indicator is shown, but after 1 sec, application locks and waits SYNCHRONOUSLY for encryption complete. If I remove Task.Delay, application lock and unlocks after operation finished.

How to use properly await and asyc in my case? I want simply execute method encryptor.EncryptAsync() asynchronously.

Cryptography is hard. Do not invent your own encryption. — SLaks
– SLaks, Commented Jun 2, 2013 at 19:59
That's even worse. Do not mislead your users into thinking that you will actually protect their data. Creating a real security product along these lines is an extremely complicated task. Read Bruce Schneier's blog. — SLaks
– SLaks, Commented Jun 2, 2013 at 20:06
It's just a student's application. Simple, without any complex logic and secure systems. — Fka
– Fka, Commented Jun 2, 2013 at 20:12

SLaks · Accepted Answer · 2013-06-02 19:57:40Z

4

The async / await keywords do not allow you to create new asynchrony; instead, they simply allow you to wait for an existing asynchronous operation to complete.

You want to run your CPU-bound operation on a background thread to avoid blocking the UI.
To do that, call the synchronous blocking method inside a lambda passed to Task.Run().

You can then use await to wait for the resulting asynchronous operation (a Task instance).

answered Jun 2, 2013 at 19:57

SLaks

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11 Comments

ilansch Over a year ago

Try msdn.microsoft.com/en-us/library/vstudio/hh191443.aspx that is very basic article and good sample that contains waiting on async with Task that return int

Fka Over a year ago

I wrote: private async void Encryption() { ShowBusyIndicator(); await Task.Run(() => encryptor.EncryptAsync()); HideBusyIndicator(); } Works!

ilansch Over a year ago

Why do you await on Task.Run ?

SLaks Over a year ago

@ilansch: To make HideBusyIndicator() run after the task finishes.

ilansch Over a year ago

Pardon me asking but if you await a task, doesnt it start the task and wait for it to complete before heading the next line ?

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