Read up on Cancellation (which was introduced in .NET 4.0 and is largely unchanged since then) and the Task-Based Asynchronous Pattern, which provides guidelines on how to use CancellationToken with async methods. To summarize, you pass a CancellationToken into each method that supports cancellation, and that method must check it periodically. private async Task TryTask() … Read more
After you use WhenAll, you can pull the results out individually with await: var catTask = FeedCat(); var houseTask = SellHouse(); var carTask = BuyCar(); await Task.WhenAll(catTask, houseTask, carTask); var cat = await catTask; var house = await houseTask; var car = await carTask; You can also use Task.Result (since you know by this point … Read more
It’s somewhat weird to read but yes, the exception will bubble up to the calling code – but only if you await or Wait() the call to Foo. public async Task Foo() { var x = await DoSomethingAsync(); } public async void DoFoo() { try { await Foo(); } catch (ProtocolException ex) { // The … Read more
Task.WaitAll blocks the current thread until everything has completed. Task.WhenAll returns a task which represents the action of waiting until everything has completed. That means that from an async method, you can use: await Task.WhenAll(tasks); … which means your method will continue when everything’s completed, but you won’t tie up a thread to just hang … Read more
This is likely TL;DR for many, but, I think comparing await with BackgroundWorker is like comparing apples and oranges and my thoughts on this follow: BackgroundWorker is meant to model a single task that you’d want to perform in the background, on a thread pool thread. async/await is a syntax for asynchronously awaiting on asynchronous … Read more
Updated: the latest version of the WebBrowser-based console web scraper can be found on Github. Updated: Adding a pool of WebBrowser objects for multiple parallel downloads. Do you have an example of how to do this in a console app by any chance? Also I don’t think webBrowser can be a class variable because I … Read more
Update: ASP.NET Core does not have a SynchronizationContext. If you are on ASP.NET Core, it does not matter whether you use ConfigureAwait(false) or not. For ASP.NET “Full” or “Classic” or whatever, the rest of this answer still applies. Original post (for non-Core ASP.NET): This video by the ASP.NET team has the best information on using … Read more
If you just want simple parallelism, you can do this: var bag = new ConcurrentBag<object>(); var tasks = myCollection.Select(async item => { // some pre stuff var response = await GetData(item); bag.Add(response); // some post stuff }); await Task.WhenAll(tasks); var count = bag.Count; If you need something more complex, check out Stephen Toub’s ForEachAsync post.
In computer science terms, a Task is a future or a promise. (Some people use those two terms synonymously, some use them differently, nobody can agree on a precise definition.) Basically, a Task<T> “promises” to return you a T, but not right now honey, I’m kinda busy, why don’t you come back later? A Thread … Read more
The whole idea behind Parallel.ForEach() is that you have a set of threads and each thread processes part of the collection. As you noticed, this doesn’t work with async–await, where you want to release the thread for the duration of the async call. You could “fix” that by blocking the ForEach() threads, but that defeats … Read more