CSharp Assíncrono - Speaker Deck

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C# Assíncrono Os segredos por trás de async e await Alex Tercete tercete@vtex.com.br

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Assíncrono?

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https://www.flickr.com/photos/snekse/2501155494

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2 minutos 5 minutos

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8 funcionários 12 clientes atendidos 21 minutos

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Não funciona

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8 funcionários 16 clientes atendidos 19 minutos

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47% mais eficiente

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Síncrono Assíncrono

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I/O Rede Banco de dados Sistema de arquivos Paralelismo

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.NET 1.1+ APM public interface IAsynchronousProgrammingModel { IAsyncResult BeginSomething( AsyncCallback callback, object state); T EndSomething(IAsyncResult result); } https://gist.github.com/alextercete/f34691cb9e4df4d2e78b

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.NET 1.1+ APM public class AsynchronousProgrammingModelWrapper { private readonly IAsynchronousProgrammingModel _apm; // Constructor public Task SomethingAsync() { return Task.Factory.FromAsync( _apm.BeginSomething, _apm.EndSomething, null); } } https://gist.github.com/alextercete/f34691cb9e4df4d2e78b

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.NET 4.0+ TPL public interface IDependency { Task BeforeAsync(); Task AfterAsync(object result); } https://gist.github.com/alextercete/a011bafde7187104303b

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.NET 4.0+ TPL public interface IDependency { Task BeforeAsync(); Task AfterAsync(object result); } https://gist.github.com/alextercete/a011bafde7187104303b

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.NET 4.0+ TPL public class TaskParallelLibrary { private readonly IDependency _dependency; // Constructor public Task SomethingAsync() { return _dependency.BeforeAsync().ContinueWith( previous => _dependency.AfterAsync(previous.Result) ).Unwrap(); } } https://gist.github.com/alextercete/a011bafde7187104303b

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.NET 4.5+ async/await public class TaskParallelLibrary { private readonly IDependency _dependency; // Constructor public async Task SomethingAsync() { var result = await _dependency.BeforeAsync(); return await _dependency.AfterAsync(result); } } https://gist.github.com/alextercete/a011bafde7187104303b

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Use async/await

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Os 8 erros mais comuns O #5 vai fazer você se emocionar

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public interface IDependency { Task BeforeAsync(); Task AfterAsync(object result); Task SomethingAsync(); Task SomethingAsync(CancellationToken token); Task SomethingAsync( Func> callback); } https://gist.github.com/alextercete/1acbaf93605383fcea51

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#1 O código quase assíncrono

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public class TheAlmostAsync { // Private fields and constructor public T Something() { return SomethingAsync().Result; } public async Task SomethingAsync() { var result = await _dependency.BeforeAsync(); return await _dependency.AfterAsync(result); } } https://gist.github.com/alextercete/1acbaf93605383fcea51

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https://www.flickr.com/photos/justinjensen/4710621230

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return SomethingAsync().Result; Something Thread x

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return SomethingAsync().Result; Something Contexto Thread x

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return SomethingAsync().Result; Something SomethingAsync var result = await _dependency.BeforeAsync(); return await _dependency.AfterAsync(result); Contexto Thread y Thread x

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return SomethingAsync().Result; Something SomethingAsync var result = await _dependency.BeforeAsync(); return await _dependency.AfterAsync(result); Contexto Thread y Thread x

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public class TheAlmostAsyncFixed { // Private fields and constructor public T Something() { return SomethingAsync().Result; } public async Task SomethingAsync() { var result = await _dependency.BeforeAsync().ConfigureAwait(false); return await _dependency.AfterAsync(result).ConfigureAwait(false); } } https://gist.github.com/alextercete/1acbaf93605383fcea51

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Use .ConfigureAwait(false) em código de bibliotecas

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#2 O código pseudo-assíncrono

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public class ThePseudoAsync { public async Task SomethingAsync() { return default(T); } } https://gist.github.com/alextercete/1acbaf93605383fcea51

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public class ThePseudoAsync { public async Task SomethingAsync() { return default(T); } } https://gist.github.com/alextercete/1acbaf93605383fcea51

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Síncrono até encontrar o primeiro ponto de assincronia

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#3 O código super-assíncrono

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public class TheSuperAsync { // Private fields and constructor public async Task SomethingAsync() { return await _dependency.SomethingAsync( async result => await _dependency.AfterAsync(result)); } } https://gist.github.com/alextercete/1acbaf93605383fcea51

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public class TheSuperAsyncFixed { // Private fields and constructor public Task SomethingAsync() { return _dependency.SomethingAsync( result => _dependency.AfterAsync(result)); } } https://gist.github.com/alextercete/1acbaf93605383fcea51

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Evite async/await quando não for necessário

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#4 O retorno nulo

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public class TheNullReturn { // Private fields and constructor public Task AfterAsync(object result) { if (result == null) return null; return _dependency.AfterAsync(result); } } https://gist.github.com/alextercete/1acbaf93605383fcea51

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public class TheNullReturnFixed where T : class { // Private fields and constructor public Task AfterAsync(object result) { if (result == null) return Task.FromResult(null); return _dependency.AfterAsync(result); } } https://gist.github.com/alextercete/1acbaf93605383fcea51

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#5 O contexto perdido

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Verifique se isso está em seu Web.config

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public class TheMissingContext { // Private fields and constructor public async Task SomethingAsync() { var result = await _dependency.BeforeAsync() .ConfigureAwait(false); // HttpContext.Current == null return await _dependency.AfterAsync(result) .ConfigureAwait(false); } } https://gist.github.com/alextercete/1acbaf93605383fcea51

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public class TheMissingContextFixed { // Private fields and constructor public async Task SomethingAsync() { var context = HttpContext.Current; var result = await _dependency.BeforeAsync() .ConfigureAwait(false); HttpContext.Current = context; return await _dependency.AfterAsync(result) .ConfigureAwait(false); } } https://gist.github.com/alextercete/1acbaf93605383fcea51

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#6 A chamada esquecida

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public class TheForgottenCall { // Private fields and constructor public Task SomethingAsync() { SomethingNotAsync(); return CompletedTask; } private async void SomethingNotAsync() { await _dependency.BeforeAsync(); } } https://gist.github.com/alextercete/1acbaf93605383fcea51

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https://gist.github.com/alextercete/1acbaf93605383fcea51 public class TheForgottenCall { // Private fields and constructor public Task SomethingAsync() { SomethingNotAsync(); return CompletedTask; } private async void SomethingNotAsync() { await _dependency.BeforeAsync(); } } private static Task CompletedTask { get { return Task.FromResult(0); } }

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public class TheForgottenCallFixed { // Private fields and constructor public async Task SomethingAsync() { await SomethingNowAsync(); } private async Task SomethingNowAsync() { await _dependency.BeforeAsync(); } } https://gist.github.com/alextercete/1acbaf93605383fcea51

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Nunca use async void

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public class TheForgottenCall { // Private fields and constructor public Task AfterAsync(object result) { _dependency.AfterAsync(result); return CompletedTask; } } https://gist.github.com/alextercete/1acbaf93605383fcea51

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public class TheForgottenCallFixed { // Private fields and constructor public async Task AfterAsync(object result) { await _dependency.AfterAsync(result); } } https://gist.github.com/alextercete/1acbaf93605383fcea51

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public class TheForgottenCallReallyFixed { // Private fields and constructor public Task AfterAsync(object result) { return _dependency.AfterAsync(result); } } https://gist.github.com/alextercete/1acbaf93605383fcea51

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#7 O cancelamento ignorado

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public class TheIgnoredCancellation { // Private fields and constructor public Task SomethingAsync(CancellationToken token) { return _dependency.SomethingAsync(); } } https://gist.github.com/alextercete/1acbaf93605383fcea51

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public class TheIgnoredCancellationFixed { // Private fields and constructor public Task SomethingAsync(CancellationToken token) { return _dependency.SomethingAsync(token); } } https://gist.github.com/alextercete/1acbaf93605383fcea51

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O cancelamento depende de quem observa o token

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#8 A disputa pelas threads

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public class TheThreadsDispute { // Private fields and constructor public T Something() { return Task.Run(() => _dependency.SomethingAsync()).Result; } public IList Somethings(int count) { var results = new List(count); Parallel.For(0, count, i => results[i] = _dependency.SomethingAsync().Result); return results; } } https://gist.github.com/alextercete/1acbaf93605383fcea51

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https://www.flickr.com/photos/eustaquio/10556254584

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Thread Pool Requests Queue

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Thread Pool Requests Queue

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Thread Pool Requests Queue

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Thread Pool Requests Queue

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Thread Pool Requests Queue

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Thread Pool Requests Queue

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Thread Pool Requests Queue

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Thread Pool Requests Queue

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Thread Pool Requests Queue

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Thread Pool Requests Queue

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Thread Pool Requests Queue

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Thread Pool Requests Queue

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Thread Pool Requests Queue

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Em cenários de alta concorrência, economize threads

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public class TheThreadsDisputeFixed { // Private fields and constructor public T Something() { return _dependency.SomethingAsync().Result; } public IList Somethings(int count) { var results = new List(count); Parallel.For(0, count, i => results[i] = _dependency.SomethingAsync().Result); return results; } } https://gist.github.com/alextercete/1acbaf93605383fcea51

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public class TheThreadsDisputeFixed { // Private fields and constructor public T Something() { return _dependency.SomethingAsync().Result; } public IList Somethings(int count) { var tasks = Enumerable.Range(0, count).Select( i => _dependency.SomethingAsync()); return Task.WhenAll(tasks).Result; } } https://gist.github.com/alextercete/1acbaf93605383fcea51

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public class TheThreadsDisputeReallyFixed { // Private fields and constructor public Task SomethingAsync() { return _dependency.SomethingAsync(); } public async Task> SomethingsAsync(int count) { var tasks = Enumerable.Range(0, count).Select( i => _dependency.SomethingAsync()); return await Task.WhenAll(tasks); } } https://gist.github.com/alextercete/1acbaf93605383fcea51

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https://www.flickr.com/photos/eschipul/4160817135

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https://www.flickr.com/photos/22897666@N00/6883636817

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3 minutos 15 segundos

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Se a espera for pequena, a troca de contexto não compensa

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1 minuto 10 minutos

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21 0 t

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Sempre haverá um gargalo

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5 minutos 3 minutos

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http://commons.wikimedia.org/wiki/File:Israel_Austerity.jpg

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Se a fila estiver grande, os clientes irão embora

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Dúvidas?

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Obrigado! Alex Tercete tercete@vtex.com.br

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Referências Blogs: – http://blogs.msdn.com/b/pfxteam/ – http://blog.stephencleary.com/ Talks: – The zen of async: Best practices for best performance – Async'ing Your Way to a Successful App with .NET – Async in ASP.NET

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Créditos – http://thenounproject.com/term/cash-register/41958/ – http://thenounproject.com/term/lunch/62503/ – http://thenounproject.com/term/server/33544/ – http://thenounproject.com/term/server/32430/ – http://thenounproject.com/term/server/32429/ – http://thenounproject.com/term/server/32431/ – http://thenounproject.com/term/lock/5427/ – http://thenounproject.com/term/hour-glass/16705/ – http://thenounproject.com/term/money/27047/ – http://thenounproject.com/term/printer/1235/