Asynchronous programming in ASP.NET
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The document covers asynchronous programming in ASP.NET, emphasizing the differences between synchronous and asynchronous operations, threading concepts, and the various async patterns supported by the .NET framework. It details implementations in ASP.NET WebForms, MVC, and WebAPI, including best practices and potential pitfalls. Key topics include handling timeouts, optimizing thread management, and ensuring performance through proper async usage.
![Timeouts in MVC and WebAPI
• Use AsyncTimeoutAttribute on async actions
• When timeout occurs TimeoutException is thrown
from action
• Default timeout is AsyncManager’s 45000 milliseconds
• Might want to catch errors
[AsyncTimeout(2000)]
[HandleError(ExceptionType=typeof(TimeoutException))]
public async Task<ActionResult> SomeMethodAsync(CancellationToken token)
{
// Pass down CancellationToken to other async method calls
…
}](https://image.slidesharecdn.com/asynchronousprogramminginasp-160724223206/85/Asynchronous-programming-in-ASP-NET-26-320.jpg)
Asynchronous programming in ASP.NET
- 2. Name: Role: https://nl.linkedin.com/in/alexthissen @alexthissen http://blog.alexthissen.nl Alex Thissen Lead Consultant, Xpirit Introducing myself
- 3. Agenda • Introduction on synchronicity • Threading and async programming in .NET • Details for • ASP.NET WebForms • ASP.NET MVC • ASP.NET WebAPI • ASP.NET SignalR • Gotchas • Questions and Answers
- 4. Talking about synchronicity Primer on async and multi-threading in Windows and .NET
- 5. (A)Synchronous in a web world Message Exchange Patterns Parallelization vs. multi- threading High Latency vs high throughput Asynchronicity is easy now Blocking operations Asynchronous is faster
- 6. A tale of fast food restaurants
- 7. Threading in Windows and .NET • Two concurrency types in Windows Operating System 1. Worker threads Physical units of work 2. IO Completion Ports Special construct for async I/O bound operations • Threads incur overhead • But threads waiting for IO Completion Port are efficient
- 8. .NET Threading primitives • System.Threading namespace • Threads: Thread and ThreadPool • Locks: Mutex, WaitHandle, Semaphore, Monitor, Interlocked • ThreadPool cannot scale hard (2 extra threads/second) • Each .NET logical thread adds overhead (1MB of managed memory) .NET 4.5 Worker Threads Completion Port Threads Minimum 4 4 Maximum 5000 (4095) 1000
- 9. Threading in ASP.NET Application Pool (w3wp.exe) CLR Threadpool Request Queue AppDomain Website http.sys IIS Unmanaged execution Kernel level … … Global Queue connectionManagement maxconnection httpRuntime/ minFreeThreads minLocalRequestFreeThreads processModel/ maxWorkerThreads minWorkerThreads maxIoThreads Outgoing connections applicationPool/ maxConcurrentRequestsPerCpu Worker Threads Completion Port Threads
- 10. Making a choice for (a)sync Synchronous • Operations are simple or short-running • Simplicity over efficiency • CPU-bound operations Asynchronous • Ability to cancel long- running tasks • Parallelism over simplicity • Blocking operations are bottleneck for performance • Network or I/O bound operations
- 11. Worker thread #1 Worker thread #2Worker thread #3 IO Completion Port Thread #3 Threads types and context switches ASP.NET Runtime Store Customers Async Windows IO Completion Port db.Save ChangesAsync Must support async pattern in some way As an example, Entity Framework 6 has support for async operations Unnecessary additional threads only occur overhead. Underlying SqlClient uses IO Completion Port for async I/O operation
- 12. Asynchronous programming .NET Framework support for async
- 13. History of .NET async programming Asynchronous Programming ModelAPM • Pairs of Begin/End methods • Example: FileStream.BeginWrite and FileStream.EndWrite • Convert using TaskFactory and TaskFactory<TResult> Event-based Asynchronous PatternEAP • Pairs of OperationAsync method and OperationCompleted event • Example: WebClient.DownloadStringAsync and WebClient.DownloadStringCompleted • TaskCompletionSource<T> to the rescue Task-based Asynchronous PatternTAP • Task and Task<T> • Preferred model
- 14. Async in .NET BCL classes • .NET Framework classes show each async style • Sometimes even mixed • Example: System.Net.WebClient • TPL (Task-based) APIs are preferred • Find and use new classes that support TAP natively
- 15. Async constructs in ASP.NET • ASP.NET runtime • Async Modules • Async Handlers • ASP.NET WebForms • AddOnPreRenderComplete • PageAsyncTask • ASP.NET MVC and WebAPI • Async actions
- 16. ASP.NET WebForms ASP.NET specifics part 1
- 17. Asynchronous programming in WebForms Your options: 1. Asynchronous pages 2. AsyncTasks It all comes down to hooking into async page lifecycle
- 18. Normal synchronous page lifecycle for ASP.NET WebForms … … LoadComplete PreRender PreRenderComplete SaveViewState Client Request page Send response Render … Thread 1
- 19. Switch to asynchronous handling … … LoadComplete PreRender PreRenderComplete SaveViewState Client Send response Render … Thread 1 Thread 2 IAsyncResult Request page
- 20. Async pages in WebForms Recipe for async pages • Add async="true" to @Page directive or <pages> element in web.config • Pass delegates for start and completion of asynchronous operation in AddOnPreRenderCompleteAsync method • Register event handler for PreRenderComplete private void Page_Load(object sender, EventArgs e) { this.AddOnPreRenderCompleteAsync( new BeginEventHandler(BeginAsynchronousOperation), new EndEventHandler(EndAsynchronousOperation)); this.PreRenderComplete += new EventHandler(LongRunningAsync_PreRenderComplete); }
- 21. PageAsyncTasks • Single unit of work • Encapsulated by PageAsyncTask class • Support for APM and TPL (new in ASP.NET 4.5) • Preferred way over async void event handlers • Can run multiple tasks in parallel // TAP async delegate as Page task RegisterAsyncTask(new PageAsyncTask(async (token) => { await Task.Delay(3000, token); }));
- 22. ASP.NET MVC and WebAPI ASP.NET specifics part 2
- 23. Async support in MVC • AsyncController (MVC3+) • Split actions in two parts 1. Starting async: void IndexAsync() 2. Completing async: ActionResult IndexCompleted(…) • AsyncManager • OutstandingOperations Increment and Decrement • Task and Task<ActionResult> (MVC 4+) • Async and await (C# 5+)
- 24. Async actions in ASP.NET MVC From synchronous public ActionResult Index() { // Call synchronous operations return View("Index", GetResults()); } To asynchronous public async Task<ActionResult> IndexAsync() { // Call operations asynchronously return View("Index", await GetResultsAsync()); }
- 25. Timeouts • Timeouts apply to synchronous handlers • Default timeout is 110 seconds (90 for ASP.NET 1.0 and 1.1) • MVC and WebAPI are always asynchronous • Even if you only use synchronous handlers • (Server script) timeouts do not apply <system.web> <compilation debug="true" targetFramework="4.5"/> <httpRuntime targetFramework="4.5" executionTimeout="5000" /> </system.web>
- 26. Timeouts in MVC and WebAPI • Use AsyncTimeoutAttribute on async actions • When timeout occurs TimeoutException is thrown from action • Default timeout is AsyncManager’s 45000 milliseconds • Might want to catch errors [AsyncTimeout(2000)] [HandleError(ExceptionType=typeof(TimeoutException))] public async Task<ActionResult> SomeMethodAsync(CancellationToken token) { // Pass down CancellationToken to other async method calls … }
- 27. ASP.NET SignalR async notes • In-memory message bus is very fast • Team decided not to make it async • Sending to clients is • always asynchronous • on different call-stack
- 28. Beware of the async gotchas • Cannot catch exceptions in async void methods • Mixing sync/async can deadlock threads in ASP.NET • Suboptimal performance for regular awaits Best practices for async: • Avoid async void • Async all the way • Configure your wait
- 29. Tips • Don’t do 3 gotcha’s • Avoid blocking threads and thread starvation • Remember I/O bound (await) vs. CPU bound (ThreadPool, Task.Run, Parallel.For) • Thread management: • Avoid creating too many • Create where needed and reuse if possible • Try to switch to IO Completion Port threads • Look for BCL support
- 30. Summary • Make sure you are comfortable with • Multi-threading, parallelism, concurrency, async and await • ASP.NET fully supports TPL and async/await • WebForms • MVC • WebAPI • Great performance and scalability comes from good thread management • Be aware of specific ASP.NET behavior
Editor's Notes
- #10: http://support.microsoft.com/kb/821268
- #11: http://www.asp.net/web-forms/overview/performance-and-caching/using-asynchronous-methods-in-aspnet-45
- #22: http://blogs.msdn.com/b/pfxteam/archive/2012/05/31/what-s-new-for-parallelism-in-visual-studio-2012-rc.aspx
- #28: http://stackoverflow.com/questions/19193451/should-signalr-server-side-methods-be-async-when-calling-clients
- #29: http://msdn.microsoft.com/en-us/magazine/jj991977.aspx