Async Await Behind Scenes
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Did you know that the .NET compiler turns our async methods into classes? And that .NET adds a try/catch block to each of these classes, potentially hiding thrown exceptions? It's true! In this session, we will learn how to best use async/await in C# by analyzing how .NET compiles our async code. Join me as we take an existing app and optimize its async code together, showing off performance gains, better exception handling, improved run-time speed, and smaller app size!
![@TheCodeTraveler https://codetraveler.io/kcdc-async-await/
async Task ReadDataFromUrl(string url)
{
WebClient wc = new WebClient();
byte[] result = await wc.DownloadDataTaskAsync(url);
string data = Encoding.ASCII.GetString(result);
LoadData(data);
}](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
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Async Await Behind Scenes
- 2. @TheCodeTraveler https://codetraveler.io/kcdc-async-await/ async Task ReadDataFromUrl(string url) { WebClient wc = new WebClient(); byte[] result = await wc.DownloadDataTaskAsync(url); string data = Encoding.ASCII.GetString(result); LoadData(data); }
- 3. @TheCodeTraveler https://codetraveler.io/kcdc-async-await/ async Task ReadDataFromUrl(string url) { WebClient wc = new WebClient(); byte[] result = await wc.DownloadDataTaskAsync(url); string data = Encoding.ASCII.GetString(result); LoadData(data); } Thread 1
- 4. @TheCodeTraveler https://codetraveler.io/kcdc-async-await/ async Task ReadDataFromUrl(string url) { WebClient wc = new WebClient(); byte[] result = await wc.DownloadDataTaskAsync(url); string data = Encoding.ASCII.GetString(result); LoadData(data); } Thread 2* *Can be any thread other than Thread 1 e.g. Thread 32
- 5. @TheCodeTraveler https://codetraveler.io/kcdc-async-await/ async Task ReadDataFromUrl(string url) { WebClient wc = new WebClient(); byte[] result = await wc.DownloadDataTaskAsync(url); string data = Encoding.ASCII.GetString(result); LoadData(data); } Thread 1
- 7. @TheCodeTraveler https://codetraveler.io/kcdc-async-await/ async Task ReadDataFromUrl(string url) { WebClient wc = new WebClient(); byte[] result = await wc.DownloadDataTaskAsync(url); string data = Encoding.ASCII.GetString(result); LoadData(data); }
- 8. @TheCodeTraveler https://codetraveler.io/kcdc-async-await/ async Task ReadDataFromUrl(string url) { WebClient wc = new WebClient(); byte[] result = await wc.DownloadDataTaskAsync(url); string data = Encoding.ASCII.GetString(result); LoadData(data); } private sealed class <ReadDataFromUrl>d_1 : IAsyncStateMachine
- 9. @TheCodeTraveler https://codetraveler.io/kcdc-async-await/ async Task ReadDataFromUrl(string url) { WebClient wc = new WebClient(); byte[] result = await wc.DownloadDataTaskAsync(url); string data = Encoding.ASCII.GetString(result); LoadData(data); } private string <data>5_3; private byte[] <result>5_2; private WebClient <wc>5_1; public string url;
- 10. @TheCodeTraveler https://codetraveler.io/kcdc-async-await/ async Task ReadDataFromUrl(string url) { WebClient wc = new WebClient(); byte[] result = await wc.DownloadDataTaskAsync(url); string data = Encoding.ASCII.GetString(result); LoadData(data); } private void MoveNext();
- 11. @TheCodeTraveler https://codetraveler.io/kcdc-async-await/ public void MoveNext() { uint num = (uint)this.$PC; this.$PC = -1; try { switch (num) { case 0: this.<wc>__0 = new WebClient(); this.$awaiter0 = this.<wc>__0.DownloadDataTaskAsync(this.url).GetAwaiter(); this.$PC = 1; ... return; break; case 1: this.<result>__1 = this.$awaiter0.GetResult(); this.<data>__2 = Encoding.ASCII.GetString(this.<result>__1); this.$this.LoadData(this.<data>__2); break; default: return; } } catch (Exception exception) { ... } this.$PC = -1; this.$builder.SetResult(); }
- 12. @TheCodeTraveler https://codetraveler.io/kcdc-async-await/ public void MoveNext() { uint num = (uint)this.$PC; this.$PC = -1; try { switch (num) { case 0: this.<wc>__0 = new WebClient(); this.$awaiter0 = this.<wc>__0.DownloadDataTaskAsync(this.url).GetAwaiter(); this.$PC = 1; ... return; break; case 1: this.<result>__1 = this.$awaiter0.GetResult(); this.<data>__2 = Encoding.ASCII.GetString(this.<result>__1); this.$this.LoadData(this.<data>__2); break; default: return; } } catch (Exception exception) { ... } this.$PC = -1; this.$builder.SetResult(); } case 0: this.<wc>__0 = new WebClient(); this.$awaiter0 = this.<wc>__0.DownloadDataTaskAsync(this.url).GetAwaiter(); this.$PC = 1; ... return;
- 13. @TheCodeTraveler https://codetraveler.io/kcdc-async-await/ public void MoveNext() { uint num = (uint)this.$PC; this.$PC = -1; try { switch (num) { case 0: this.<wc>__0 = new WebClient(); this.$awaiter0 = this.<wc>__0.DownloadDataTaskAsync(this.url).GetAwaiter(); this.$PC = 1; ... return; break; case 1: this.<result>__1 = this.$awaiter0.GetResult(); this.<data>__2 = Encoding.ASCII.GetString(this.<result>__1); this.$this.LoadData(this.<data>__2); break; default: return; } } catch (Exception exception) { ... } this.$PC = -1; this.$builder.SetResult(); } case 1: this.<result>__1 = this.$awaiter0.GetResult(); this.<data>__2 = Encoding.ASCII.GetString(this.<result>__1); this.$this.LoadData(this.<data>__2); break;
- 14. @TheCodeTraveler https://codetraveler.io/kcdc-async-await/ public void MoveNext() { uint num = (uint)this.$PC; this.$PC = -1; try { switch (num) { case 0: this.<wc>__0 = new WebClient(); this.$awaiter0 = this.<wc>__0.DownloadDataTaskAsync(this.url).GetAwaiter(); this.$PC = 1; ... return; break; case 1: this.<result>__1 = this.$awaiter0.GetResult(); this.<data>__2 = Encoding.ASCII.GetString(this.<result>__1); this.$this.LoadData(this.<data>__2); break; default: return; } } catch (Exception exception) { ... } this.$PC = -1; this.$builder.SetResult(); } try { catch (Exception exception) { . . . }
Editor's Notes
- Every time we add the `async` keyword, the compiler creates a new class. Each class increases our app size by appx. 100 bytes
- Every time we add the `async` keyword, the compiler creates a new class. Each class increases our app size by appx. 100 bytes
- Every time we add the `async` keyword, the compiler creates a new class. Each class increases our app size by appx. 100 bytes