How to use Async/Await/Task in C#
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- čas přidán 18. 04. 2020
- In this tutorial we take a look at how to use async, await and Task in C#. Primarily looking at good practices and how to avoid common pitfalls such as creating unecessary state machines, blocking threads, using ConfigureAwait when making libraries and how to avoid async in constructors.
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Karel Zikmund • Async demystified - Ka...
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Very helpful follow up video for some solid DO's and DON'Ts fundamentals.
you're the man! thanks for your dedication
Thank you))
Wow, it has come such a long way. I remember about 10+ years ago, don’t really know how early WPF was at the time, was trying to understand MVVM patterns, XAML as the view, etc and the whole thing had a ‘Dispatcher’, ‘Context’, etc for jobs , to force the results to be piped to the main UI thread (if I remember right).
Now by default it joins the UI thread... and code is written quite linearly.
This is magic. Thanks for the dedication in sharing this.
Thank you for watching and sharing some history :)
good and simple example of using these topics. thanks for the video!
I learned fundamental more clearly.. great video. Thanks for your great dedications :)
Thank you :)
Awesome. Subscribed. Helped me a ton.
Awesome!
Very well explained. Thanks!
Thank you
Awesome delivery of the content: clear and engaging. 👍
Cheers)
Love your content! More power to you
Thank you
Thanks for video, that helps a lot!
Thanks for explanation!
Great video!
You make my day man.
Again, very good video, It was interesting and informative to watch the video. Could you please share some link with description, why we should avoid using of 'async' and 'Task' together in one method?
In my previous video I show you that async creates a state machine, you want to avoid making a state machine but not sacrifice readability.
Ur channel is a gold mine :D
👍 very nicely explained
Thank you
You really made my day.
Спасибо за видео!)
Спасибо что посмотрел )
@@RawCoding Do you speak Russian as well?
Yes
Nice content. I kind liked the idea to help fellow techies by creating videos. And that's why i also started doing Azure videos.
Awesome, wishing you luck :)
@@RawCoding Thanks!
would be cool to see why should we avoid those that you marked or said BAD/Dont do this, some explanation on what could go wrong with those
Cool
this is good. thanss
Cheers
I believe if we don't use ConfigureAwait or use ConfigureAwait(true), then after returning from await it does not execute on calling thread, it's just calling thread context is stored, and when network driver hands the result to one of the threadpool thread.. the saved context of the calling thread is copied into this threadpool thread (meaning the code after await still execute of the threadpool thread not on the calling thread). It's applicable for Dotnet framework not asp.net core since core do not have any SynchronizationContext .
Sounds reasonable
Thank you for another great video.
Question: On a web-app, should I await my task inside the view, or should I await the task in the controller, and then populate my view-model with the data?
Should a view-model contain tasks?
The View can contain and execute tasks with await, that's not a problem. But you want to create the model outside the view.
@@RawCoding Thank you for another great video. as you said, "The View can contain and execute tasks with await" so what if I use postman or jquery to send request ? Could it handle task or not ?
What? Task is a c# construct
Hi there, how does the runtime decides that the thread it frees while processing a long asynchronous task, will not be assigned to a synchronous task? Or can it be assigned to any request/task regardless of asynchronous or not?
It's a bit incorrect to think that you put tasks on threads, it's more like there is a pile of tasks (objects) and threads eat (process) from that pile.
1. eat task
2. reach await and stop eating
3. wait for interrupt from IO hardware component to reach runtime and then runtime instructs the thread pool to assign a thread to eating the task again
the "eating" motion is re-entering the task (state machine object), if the task contains a blocking operation (lock) the thread pool will be stuck trying to eat the task. A thread cannot eat 2 tasks at the same time. It can be told to eat 1 task and then once it completed a step in the state machine it can be told to eat another task.
Hope this helps
Great content,can you make some tutorials for SignalR?
I have one it’s not great.
Raw Coding hmm maybe create a playlist because i can’t find much high quality tutorials on it
In the future, SignalR isn’t complicated you shouldn’t have a problems implementing it.
I enjoy your videos and am watching more. I need to start a side ASYNC process that checks the internet API every 30 seconds and then updates a flag so I can set an icon to green, Been struggling with the ASYNC and wanted to know if you hve done this before and can offer some coaching?
Come ask your question on discord with code examples
@@RawCoding I am new to the youtube channel stuff. What is discord?
It’s like a server with chats n stuff for discussion, link is in the description of the video
Thanks for this awesome explanation!
I have one question. A process has thread(s) and within a process thread(s) share memory. Then why do we need a certain thread for UI?
The problem with the ui thread is something you don’t see you need something to say draw pixels on screen, having multiple threads write to screen is not a thing kind of like writing to the same file in parallel.
@@RawCoding Fair-enough :) Thank you!
@@RawCoding In web development, I think I found our UI thread. So in a Blazor Server app, I have a component:
Counter: @Counter
Start Timer
@code {
public int Counter { get; set; }
private void StartTimer()
{
Timer timer = new Timer(TimeCallBack, null, 1000, 1000);
}
private void TimeCallBack(object state){
if(Counter < 5)
{
Counter++;
Console.WriteLine("Counter " + Counter);
// Use InvokeAsync to switch back to the UI thread before triggering UI update
InvokeAsync(() => StateHasChanged());
// TimeCallBack method executed by another thread?
// StateHasChanged();
}
}
}
First I used StateHasChanged(); Simply, I wanted to re-render my component but I got this error: The current thread is not associated with the Dispatcher. Use InvokeAsync() to switch execution to the Dispatcher when triggering rendering or component state.
It seems like a perfect example of UI thread importance. Can you confirm my assumption?
I"m trying to learn sockets and I'm new to C# and am overwhelmed with all the different libraries you can use and all the ways to do it. Each example is pretty much incompatible with every other example. I came across one that used await and it's the only one that shows how a server can message a webpage. Anyway I can't get that example to receive a message. All I get is numbers. It seems that the best method for chat might be callbacks. So that's another situation where the same thing can be done in many ways. Callbacks vs async await. You would think that the machine could handle just waiting for a response in some cases just for development speed. Anyway I'm thinking the best way to explain things is to explain all the different ways to handle asynchronous programming. Another one is threads. I watched your other video and you brought in threads really quickly so I guess async must create a thread behind the scenes.
the async programming model is meant to be an abstraction on top of the threads/processors, and I bring them in because we were going under the hood. The reality is you don't need to be concerned with much of that stuff, because all you are doing is you are saying some external thing is going to do some work and you don't want your application to hang. For chat app I'd reccomend looking in to signalR it's pretty good :)
I have been doing some flutter tutorials, they are nice and all but there is no one explaining how I can link up an Api in core and flutter to do a crud is it possible for you to do a crud Api with flutter and .net core tutorial
Join for my Sunday streams, I’m currently hooking up a flutter app to identity server and going to be calling the api next, stream will be uploaded on Wednesday.
@@RawCoding can't wait
Let's say I have a method like this in a repository(It's not very correct):
Task Insert(T something) => _ctx.Add(something);
But as I'm gonna use this in a wpf app I need to add ConfigureAwait(false), now the Add method returns a ConfiguredTaskAwaitable. and I cannot return Task directly. It compiles this way:
async Task Insert(T something) => await _ctx.Add(something).ConfigureAwait(false);
Is there a way to avoid creating state machine in this method?
The caller of the task would have to configureAwait false. Make a distinction between creating a task (which is what we do if we don’t await it) and executing the task which is when we await it.
@@RawCoding Thanks for replying, but looks like I can't avoid nested asyncs in here.
is there more resources that make this more clear ,it still seems confusing to me ?
What are you confused about?
could you explain the use of lock() ?
you reserve a scope of code to only be executed by 1 process at a time.
What extensions do u use to make VS symbols look pretty !?
JetBrains mono font
Thanks a lot 👊🏽
So, if you wanna do smth with the contents of a task, you have to retrieve with async/await and if you just pass the task around you can omit the async/await?
Yes
@@RawCoding I see, so a main controller method of a web api with db queries and/or email sending is likely to be async? (as an example), since we `await` to get the results of the query?
Yes
@@RawCoding Thank you
What keyboard are you using?
Flico Convertible 2 Tenkeyless MX brown, just to warn you the wireless Bluetooth isn’t perfect
@@RawCoding That's fine, thanks!
If I use Task as output in Method (without async/await) will it work asynchronous anyways? thnx!
Yes
👍🏽
)
Hi, thx for your videos. I have a question related to "do not use async in a constructor" - Why?
I've found answer for my question here -> czcams.com/video/J0mcYVxJEl0/video.html :)
What's the difference of just calling Notify() (without await) and Task.Run(() => Notify()) ?
It’s fire and forget, you never get the result back.
You say "still remain with non task main" should we always aim to have non async/task main?
It doesn't really matter that much :)
When does async and Task fit in event driven systems
At IO level
Also watch Writing async/await from scratch in C# with Stephen Toub --> czcams.com/video/R-z2Hv-7nxk/video.html
how to resolve cannot convert "void" to "system.threading.tasks.task" ??
public void Fn(){ } //
What happens if we do not await an awaitable?
You’ll never consume the result, and if you have closures they might get disposed of and crash the task
@@RawCoding but in your tutorial, you use Task. Run method like a fire and forget process. It Itslef returns a task object and we aren't awaitimg it anywhere. Whats the difference?
If the task is isolated it just runs in the background
I still can't figure out how I should avoid using state machine. In most of you examples you are using async which means using state machine. Can someone clarify this for me?
Task do() => someTask;
async Task do() => await someTask;
First example we just return the task - no need to await or use async no state machine. Second you are awaiting the task and having to use async for that - generates state machine.
You want to avoid 2 when it’s obvious. Otherwise you don’t have to worry about not creating a state machine.
@@RawCoding Thank you!
А зачем ты рекомендуешь не использовать .GetResult(), и в первой строчке входной точки программы используешь его?)
Имхо лучше показать людям как правильно, даже учитывая что компилятор все равно превратит это в .GetResult()
Прости немножко не понял, что привносится в GetResult()?
@@RawCoding возможно я не понял вопрос) но .GetResult() ведь блокирует поток и ожидает результата, а людям нужно объяснить что б использовали async/await во избежание этого)
Видео уже довольно старое, возможно мой комментарий неуместен и вы уже используете асинхронность во входной точке программы)
GetResult() блокирует и поэтому я не рекомендую его использовать; те кто понимают где это не составит проблем могут блокировать, я например пользуюсь этим в стартапе своей программы перед тем как она запускается
public async Task M1()
{
await Task.Delay(1000);
Console.Write("M1");
}
public Task M2()
{
Console.WriteLine("M2");
return Task.CompletedTask;
}
------then calling----
public async Task End1()
{
await M1();
await M2();
}
public async Task End2()
{
var t1 = M1();
var t2 = M2();
await t1;
await t2;
}
End1() call (=> M1M2) and End2() call (=> M2M1) have different results.
I dont understand why..could you explain please ? Thank you:)
End1 you await each task sequentially, end2 you kick off the 2nd task without waiting for the 1st to finish which has the delay
Please don't create new HttpClient for every request people. HttpClient is intended to be instantiated once and reused throughout the life of an application.
Tbh HttpClient is not the problem the handler is. But good advice to follow for newbies
Hey, great tutorial, thanks a lot, and i would like to recommend this video for you , because it mentions the benefits of using async/await
czcams.com/video/aaC16Fv2zes/video.html
do you have money?
Yes