Short answer A virtual method may be marked as async An abstract method cannot be marked as async The reason for this is async is not actually part of the method signature. It simply tells the compiler how to handle the compilation of the method body itself (and does not apply to overriding methods). Since … Read more
Two new keywords added to the C# 5.0 language are async and await, both of which work hand in hand to run a C# method asynchronously without blocking the calling thread. That gets across the purpose of the feature, but it gives too much “credit” to the async/await feature. Let me be very, very clear … Read more
There are probably several reasons. Here are some: Huge backwards compatibility problems How would you write the definition of ICollection<T>? This looks natural: interface ICollection<T> : IReadOnlyCollection<T> { int Count { get; } } But it has a problem, because IReadOnlyCollection<T> also declares a Count property (the compiler will issue a warning here). Apart from … Read more
I believe the TPL (TaskFactory.Startnew) works similar to ThreadPool.QueueUserWorkItem in that it queues up work on a thread in the thread pool. Pretty much. From what i’ve been reading it seems like async/await only “sometimes” creates a new thread. Actually, it never does. If you want multithreading, you have to implement it yourself. There’s a … Read more
I believe this is expected behavior because you’re running in to a variation of a race condition. From How to: Cancel a task and its children: The calling thread does not forcibly end the task; it only signals that cancellation is requested. If the task is already running, it is up to the user delegate … Read more
Avoid async void. It has tricky semantics around error handling; I know some people call it “fire and forget” but I usually use the phrase “fire and crash”. The question is: Given a synchronous method A(), how can I call it asynchronously using async/await in a fire-and-forget manner without getting a solution that is more … Read more
UPDATE: Async versions of File.ReadAll[Lines|Bytes|Text], File.AppendAll[Lines|Text] and File.WriteAll[Lines|Bytes|Text] have now been merged into .NET Core and shipped with .NET Core 2.0. They are also included in .NET Standard 2.1. Using Task.Run, which essentially is a wrapper for Task.Factory.StartNew, for asynchronous wrappers is a code smell. If you don’t want to waste a CPU thread by … Read more
They just talked about this at PDC yesterday! Await is used in conjunction with Tasks (parallel programming) in .NET. It’s a keyword being introduced in the next version of .NET. It more or less lets you “pause” the execution of a method to wait for the Task to complete execution. Here’s a brief example: //create … Read more
Update: C# 6.0 supports await in catch Old Answer: You can rewrite that code to move the await from the catch block using a flag: WebClient wc = new WebClient(); string result = null; bool downloadSucceeded; try { result = await wc.DownloadStringTaskAsync( new Uri( “http://badurl” ) ); downloadSucceeded = true; } catch { downloadSucceeded = … Read more
async void methods should be considered as “Fire and Forget” – there is no way to wait for them to finish. If Visual Studio were to start one of these tests, it wouldn’t be able to wait for the test to complete (mark it as successful) or trap any exceptions raised. With an async Task, … Read more