C# Asynchronous Programming Full Tutorial : Async / Await / Task and Deadlock Fix by ConfigureAwait

[FurkanGozukara]

C# Asynchronous Programming Full Tutorial : Async / Await / Task and Deadlock Fix by ConfigureAwait

Full tutorial: https://www.youtube.com/watch?v=I4cnX_odC1M

In this lecture video, I am going to explain #asynchronous #programming concepts when using .NET Core 7 with C# #programming language. I will code a #WPF application to demonstrate #Async, #Await, #ConfigureAwait, and #Task concepts while doing asynchronous coding. I will show how ConfigureAwait is important to prevent deadlocks while using "async" and "await" keywords.

The code repository of this lecture :

https://github.com/FurkanGozukara/C-Async-Await-Task-Deadlock-Fix-by-ConfigureAwait-Full-Tutorial-Asynchronous-Programming

Moreover, we cover the following #howto topics:

• How to do asynchronous programming with C# and .NET

• How to use Async, Await and ConfigureAwait

• How to use Task, Task.Wait and ContinueWith

• How to utilize Dispatcher.BeginInvoke to update UI elements from different tasks, sub-tasks, threads

• How to utilize Thread.CurrentThread.ManagedThreadId to see which code is executed in which thread

• How to download source of a web page / URL asynchronously and properly with using HttpClient and Content.ReadAsStringAsync

00:00:00 Introduction Task, Async, Await and composing the demo application

00:02:18 Generating Async deadlock causing example

00:08:03 How to see thread IDs during the runtime

00:11:47 How to fix deadlock

00:13:50 How to use ConfigureAwait properly

00:14:48 How to make UI responsive with proper Async Await usage

00:17:09 How to make async but main thread blocking code with TaskFactory.StartNew and Task.Wait

00:20:52 How to make fully asynchronous and non-blocking UI with TaskFactory and ContinueWith

00:23:36 How to update UI thread from sub-thread with Dispatcher

We have manually corrected the subtitles for the video so watch the tutorial with subtitles on if you have a hard time understand

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Thumbnail: Freepik (@fullvector) - Data processing, software program development, code review, database concept. #dotnet #dotnet7 #csharp

Video Transcription

• 00:00:00 Hello everyone. I am Dr. Furkan Gözükara. In this  lecture video, I am going to explain asynchronous  

• 00:00:07 programming concepts when using .NET Core 7 with  C-Sharp programming language. I will code a WPF  

• 00:00:14 application to demonstrate async, await, configure  await and task concepts while doing asynchronous  

• 00:00:21 coding. I will show how ConfigureAwait is  important to prevent deadlocks while using  

• 00:00:27 async and await keywords. Let's start coding  with composing a .NET Core 7 WPF application.  

• 00:00:33 If your Visual Studio is lacking .NET Core 7,  just download latest Visual Studio Community  

• 00:00:39 Edition and update it to the latest version. Here  let me show you how to update your Visual Studio.  

• 00:01:01 As you can see, my Visual Studio is up  to date. Its version is 17.4.1. Okay,  

• 00:01:08 so let's start composing our WPF project.  I am going to pick WPF application. You  

• 00:01:15 can also look for it with searching WPF. And  then you see there is ASP.NET Core WPF app.  

• 00:01:24 Then click next. Okay, it will  be in my desktop. Let's say  

• 00:01:32 async programming. I am going to pick .NET  7 and this is .NET Core web app. Let's fix  

• 00:01:41 it quickly. Okay, here WPF application  and it is with .NET Core. Okay, next.  

• 00:01:53 You see it says that there is WPF  application. Okay .NET Core 7.  

• 00:02:06 Okay, application is started now. The  interface is loaded. So let's start  

• 00:02:14 with generating a button control. First I will  show you how a deadlock can happen when we are  

• 00:02:23 doing asynchronous programming with async and  await keywords. Let's say test async deadlock.  

• 00:02:42 Okay and with double clicking it I  am going to compose click event here.  

• 00:02:49 Okay, so let's assume that we have an  async method that will return a string.  

• 00:02:57 Let's say return source code of  a web page as a string. Okay.  

• 00:03:18 I will use HTTP client.  

• 00:03:24 Okay and inside here we will use.  

• 00:03:34 We will use HTTP response.  

• 00:03:40 Okay. Sorry not not necessarily we need that.  

• 00:03:56 You see it has suggested me to auto complete is  like this and it's correct. And we will return.  

• 00:04:09 Response request. Content. Okay,  then let's see. Okay, like this.  

• 00:04:24 All right. However, since this is asynchronous  with async keyword. We need to say await here.  

• 00:04:34 And since this is an async method, we can't just  return it like this. We have to return a task  

• 00:04:43 like this. Okay. And let's add a label or a text  

• 00:04:49 block to display source code.  I'm going to pick a text block.  

• 00:04:57 Okay, let's name it as block source code.  

• 00:05:05 Okay, I have named it as txt block source code.  

• 00:05:10 Then let's assign text of txt block  source code equal to return source code of  

• 00:05:21 my developed web game web based game, which  is HTTPS www monsters MMORPG.com. Okay.  

• 00:05:33 However, to access result of async method, we  have to get result. So what does this async do?  

• 00:05:45 Async means that that method is asynchronous and  it will not block the thread that it is executed.  

• 00:05:58 However, to get its result,  I need to use await keyword.  

• 00:06:04 And when you use await keyword, then  you don't need to access it by result.  

• 00:06:12 So when I run this code, what will happen? Let's  see. Let's run and run our application and see.  

• 00:06:26 Okay, I am clicking it and you see it has returned  the result as expected. Because because there is a  

• 00:06:39 key issue here, you see my button click is now  also asynchronous. However, if I don't want to  

• 00:06:48 make it asynchronous, then I need to return  async keyword here that the Visual Studio  

• 00:06:54 did put automatically and I need to use result  like this. Okay, let's see now what happens.  

• 00:07:06 Okay, I'm clicking and my application  is completely frozen. Do you know why?  

• 00:07:13 Because currently the UI thread  is blocked. The reason is that UI  

• 00:07:20 thread is waiting to waiting the result  of this method call and this method call  

• 00:07:28 is not able to execute because the UI thread is  already frozen. So how can I solve this problem?  

• 00:07:40 So for solving this problem, I can use configure  await. So when you set configure await false  

• 00:07:49 on an async method, this means that this  method can now run on a different thread.  

• 00:07:59 Okay, so to see the thread IDs that each method  is running, let's use managed thread ID code.  

• 00:08:11 Okay, let's write it to our  output window with thread.  

• 00:08:23 Okay, current thread manage thread  ID. Okay, so it says that thread is  

• 00:08:27 not existing in the current context  for that I am adding using threads.  

• 00:08:34 Okay, so this will print the thread ID of the  thread that this line is executed. Then let's  

• 00:08:42 also see the thread ID here. Let's also  add some extra information as the inside  

• 00:08:54 here. Then let's also write it as like  this inside here. And then one second.  

• 00:09:08 Okay, inside the first using statement inside  using HTTP client and inside here. Okay, so  

• 00:09:28 first, let's run it without configure,  await and see which output we are getting.  

• 00:09:40 Okay, let's check out the output window. So, okay,  we see that inside btnTestAsyncDeadLock_Click,  

• 00:09:51 which is here, the thread ID is one. It is  expected because we are currently inside  

• 00:09:58 the main UI thread, and it is one and in the  source code. So it has entered here, we are  

• 00:10:06 still inside thread ID one. And then we have  entered here as well inside using HTTP client.  

• 00:10:16 However, since we are doing await here,  now it becomes asynchronous call and it  

• 00:10:27 locks our execution. And you see we didn't  enter inside here because the UI thread is  

• 00:10:37 now awaiting that response. So the main  thread is UI thread is locked, frozen.  

• 00:10:46 And this execution is waiting that thread to be  released. Okay, so when I add this execution,  

• 00:11:00 configure await as false. Now let's see  how to output. Let's see the output again.  

• 00:11:11 Okay, the button is still frozen because it is  not anymore asynchronous. However, now we can  

• 00:11:17 see inside using response. You see inside here now  running in a different thread and the thread ID is  

• 00:11:24 six. Okay, so this is where configure await is  very useful because when you set ConfigureAwait  

• 00:11:36 false, then that asynchronous method call becomes,  starts running in a different thread. Okay,  

• 00:11:48 so if we don't want the interface to be  frozen, let's copy and paste this button.  

• 00:11:54 And let's say btn test proper async  code. Okay, proper async code.  

• 00:12:05 Okay, so this will cause a deadlock,  so I'm going to delete this.  

• 00:12:13 All right. Oh, we don't need that actually.  So this is return source code with  

• 00:12:23 or let's say let's add an option here.  Bool cause deadlock equal to false. Okay.  

• 00:12:37 Okay, so if you don't want to cause deadlock,  then configure await. Then I need to  

• 00:12:46 give opposite of this. So by default it will  cause a deadlock and to cause a deadlock. We need  

• 00:12:54 to give configure await true. Okay. Maybe this  make make you confused. So let's say bl configure  

• 00:13:06 await by default. Let's make it  false so it won't cause a deadlock.  

• 00:13:13 Okay, now it won't cause a deadlock. So to cause  a deadlock, I need to provide it true. Okay. Yes,  

• 00:13:25 now it will cause a deadlock. Let's try. Okay,  so you see we are never getting inside here.  

• 00:13:36 So now it is deadlocked because main thread the  UI thread is awaiting the result and the result  

• 00:13:45 is awaiting main thread UI thread to be released  to run. Okay, so each one is awaiting each one  

• 00:13:54 and it causes a deadlock. All right, so let's  make this as none that's locking or let's say  

• 00:14:07 configure await asynchronous code. Okay,  I need to change its click event. We can  

• 00:14:18 configure await async code. Okay. This time we  are just going to run it with false and let's try.  

• 00:14:36 Okay, still, the interface is frozen during  the runtime because this button click is not  

• 00:14:42 asynchronous. However, it is not that locked.  Okay. And let's also add another button, which  

• 00:14:52 will be responsive. We can responsive. Okay, async  click. Let's say it as responsive async click.  

• 00:15:08 Okay, and I need to generate a new click event.  Okay, so I'm going to mark this method as async  

• 00:15:20 and I can also let Visual Studio to mark  it as async automatically with await.  

• 00:15:30 Okay, now you see it is  automatically marked as async. Okay,  

• 00:15:38 now in this case, it will not freeze the  interface. Let's try. Okay, let's try again.  

• 00:15:49 Okay, the interface is not freezing. However,  meanwhile, the text block is getting updated.  

• 00:15:56 During that time, the interface will freeze,  of course, because it is getting updated.  

• 00:16:02 And since source code is pretty big,  it is not displayed entirely here.  

• 00:16:09 It takes some time. Actually, maybe we can  fix it with. Okay. I don't know. Let's see.  

• 00:16:19 Max with max height, for example, let's  say 6000 and let's see what happens.  

• 00:16:28 Okay, probably we need to add scroll bars.  Let's see horizontal alignment. No scroll,  

• 00:16:37 scroll bar. Okay, scroll. No. Okay, anyway, it is  not important for this lecture. And there is one  

• 00:16:48 another methodology, one more method, actually  two more methodology. So let's also see them.  

• 00:16:54 I'm going to expand this a  little bit more. Why? Okay,  

• 00:17:07 here. Okay. Now I will use task  methodology. Okay, so btnTaskExample.  

• 00:17:17 I will call this as task version one. Okay, and  let's generate this click event. So this time I  

• 00:17:28 will start this code inside or let's say as a task  task. Let's say var task = Task.Factory.StartNew.  

• 00:17:42 Okay. It automatically completes. Very  nice. And let's call it like this.  

• 00:17:50 And by the way, still this is a async  method. So I need to call await.  

• 00:17:59 And I need to assign this into a string  variable. Let's say string source.  

• 00:18:10 Like this. And let's say the source  is equal to await.result. Okay. Okay.  

• 00:18:24 I need to provide the source code, of course.  I mean the URL. All right. And no result. Okay.  

• 00:18:34 And then what do I need to do is. I can do  task.wait. This will make it synchronous.  

• 00:18:45 And then I can assign the source like this.  Okay. It says that this can be null here. So  

• 00:18:57 let's initialize it like this. All right.  You see, it is still pretty responsive.  

• 00:19:08 But we never get the result. So in this  case. We need to set configure await true.  

• 00:19:20 Otherwise it will return from that asynchronous  and the task wait will never work. I suppose.  

• 00:19:28 Let's try. Yes, we did enter inside the request.  Okay. All right. This is the sound of my girl.  

• 00:19:42 Okay, we do. We do enter inside the request.  However, it is obvious that the source code  

• 00:19:52 is immediately executed without waiting. So  the task is completed immediately. Since we  

• 00:20:00 are doing an asynchronous call here. And  therefore, maybe we need to do. Let's see.  

• 00:20:11 Okay, we need to turn this asynchronous call into  a synchronous call because we are already spawning  

• 00:20:18 a new task. And here we just need to provide  or let's say, get result. Okay. And we need to  

• 00:20:28 remove the wait keyword. All right. Now, since  this will run inside a different thread than the  

• 00:20:37 main thread, then it won't cause any problem as  a deadlock. However, our interface will be still  

• 00:20:46 frozen. Let's try. Okay. It is working. Now let's  make another example of task with ContinueWith. So  

• 00:20:58 I will call this task as version two. Okay.  And let's say btn task version two. All right.  

• 00:21:11 Okay. Okay. So in this case, we are  going to use a different methodology as  

• 00:21:23 continue with. All right. And it says we need a  new action. Okay. Action. Okay. And. It says task.  

• 00:21:43 Okay, one moment. It is pretty simple, actually.  So we are going to call this T1 parameter,  

• 00:21:53 which will be when we hover it, we see that it  is task T1. So this means that it is the result  

• 00:21:59 of execution of this task. Okay. And inside that  we will have the result of the task. Therefore,  

• 00:22:10 I will assign. I don't need this  anymore. The text as equal to Ok.  

• 00:22:21 T1. Okay. Result. Okay. And I just need to  return the result of the inner execution. Okay.  

• 00:22:35 Now this is supposed to not block anything  and update the text block. Let's try. Okay.  

• 00:22:41 It is not block it. Okay. Inside is called. All  right. So we have a little bit. Another problem.  

• 00:22:51 Okay. Which is this is task return. Okay.  We are waiting it. We are locking it.  

• 00:22:59 So let's try. Maybe we didn't wait. Okay. We  did enter inside. Oh, we have a system invalid  

• 00:23:08 operation exception somewhere. Okay. Let's put  a break point here. Maybe our error is there.  

• 00:23:17 Okay. And. When we debug the result. Okay. The  result is there as well. Oh, I know the reason.  

• 00:23:26 I know the problem. The problem is we cannot  update the UI element inside another task. So  

• 00:23:37 I need to do use dispatcher.  Let's say begin invoke new action.  

• 00:23:45 And inside that I need to assign it. Okay. So you  see it defines a new action like this. And it's  

• 00:23:54 anonymous call because we don't get we don't  need any parameter. Actually, it is like here,  

• 00:24:00 as you can see. But this is empty action.  And yes, now it should work. Let's try.  

• 00:24:10 OK. All right. I have shown multiple ways to use  async and task to do asynchronous programming.  

• 00:24:22 I hope you have enjoyed. Please ask your questions  in the comments section. Hopefully see you  

• 00:24:30 in another video. Let me know through comment  section that what questions do you have? What  

• 00:24:39 topics do you wonder? What would you like to see  in my next video? OK. Hopefully see you later.