In the kindergarden around the corner they use a SemaphoreSlim to control how many kids can play in the PE room. They painted on the floor, outside of the room, 5 pairs of footprints. As the kids arrive, they leave their shoes on a free pair of footprints and enter the room. Once they are … Read more
When targeting .NET 4.5 you can use Task.FromResult: public static Task<TResult> FromResult<TResult>(TResult result); To create a failed task, use Task.FromException: public static Task FromException(Exception exception); public static Task<TResult> FromException<TResult>(Exception exception); .NET 4.6 adds Task.CompletedTask if you need a non generic Task. public static Task CompletedTask { get; } Workarounds for older versions of .NET: When … Read more
SLaks and Killercam’s answers are good; I thought I’d just add a bit more context. Your first question is essentially about what methods can be marked async. A method marked as async can return void, Task or Task<T>. What are the differences between them? A Task<T> returning async method can be awaited, and when the … Read more
async Task<int> LongTask1() { … return 0; } async Task<int> LongTask2() { … return 1; } … { Task<int> t1 = LongTask1(); Task<int> t2 = LongTask2(); await Task.WhenAll(t1,t2); //now we have t1.Result and t2.Result }
You can definitely do this in the latest versions of async for .NET, using .NET 4.5 Beta. The previous post from ‘usr’ points to a good article written by Stephen Toub, but the less announced news is that the async semaphore actually made it into the Beta release of .NET 4.5 If you look at … Read more
You don’t have to do anything special, Parallel.Foreach() will wait until all its branched tasks are complete. From the calling thread you can treat it as a single synchronous statement and for instance wrap it inside a try/catch. Update: The old Parallel class methods are not a good fit for async (Task based) programming. But … Read more
It turns out that the following works: Task<x> DoStuff(…., CancellationToken ct = default(CancellationToken)) …or: Task<x> DoStuff(…., CancellationToken ct = default) // C# 7.1 and later which, according to the documentation, is interpreted the same as CancellationToken.None: You can also use the C# default(CancellationToken) statement to create an empty cancellation token.
Here’s the sequence of code snippets I recently used to illustrate the difference and various problems using async solves. Suppose you have some event handler in your GUI-based application that takes a lot of time, and so you’d like to make it asynchronous. Here’s the synchronous logic you start with: while (true) { string result … Read more
I was involved in the design and implementation of these classes. The short answer is “separation of concerns“. It is quite true that there are various implementation strategies and that some are simpler at least regarding the type system and initial learning. However, CTS and CT are intended for use in a great many scenarios … Read more
Yes, use WhenAll because it propagates all errors at once. With the multiple awaits, you lose errors if one of the earlier awaits throws. Another important difference is that WhenAll will wait for all tasks to complete even in the presence of failures (faulted or canceled tasks). Awaiting manually in sequence would cause unexpected concurrency … Read more