async

ASP.NET Core – Control the graceful shutdown time for background services

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ASP.NET Core gives you a chance to gracefully shutdown your background services (such as cleaning up and/or finishing in-progress work). By default, you’re given a grand total of 5 seconds to shutdown all background services. If you need more time than this, there are a few ways to control the graceful shutdown time, which I’ll … Read more

How to debug .NET source code in Visual Studio

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When you’re using the Visual Studio debugger to step through your code, sometimes it’s useful to be able to step into the .NET source code. I had to do this recently to figure out why my ASP.NET Core code wasn’t behaving as expected. You can enable .NET source code debugging with the following steps: Now … Read more

ASP.NET Core – Receive a request with CSV data

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There are two ways to receive CSV data in a web API: In this article, I’ll show examples of both of these approaches. I’ll be using the CsvHelper library to parse CSV data into model objects and then do model validation. Note: To use CsvHelper, install the CsvHelper package (Install-Package CsvHelper). Or use whichever parser … Read more

ASP.NET Core – How to unit test a custom InputFormatter

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In this article, I’ll show how to unit test a custom InputFormatter. The main thing to test is the output of the ReadRequestBodyAsync() method. To test this, you have to pass in an InputFormatterContext object containing the request body. As an example, I’ll show how to unit test the following ReadRequestBodyAync() method: Note: This parses … Read more

ASP.NET Core – How to receive a request with text/plain content

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When a request comes in and your action method has parameters, the framework tries to find the appropriate InputFormatter to handle deserializing the request data. There’s no built-in text/plain InputFormatter though, so when you send a request with text/plain content, it fails with a 415 – Unsupported Media Type error response. In this article, I’ll … Read more

Redirect a request in ASP.NET Core

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Redirecting a request means returning a response with redirect status code (3xx) and a redirect URL in the Location header. The client uses this info to follow the redirect (which means making a request to the redirect URL). You can redirect by using a helper method (from ControllerBase) or returning a RedirectResult. I’ll show several … Read more

Control ASP.NET behavior when background service crashes

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When a background service throws an unhandled exception in ExecuteAsync(), you have two options: You can change the behavior if the default isn’t what you want (notice the default behavior changed in .NET 6). In .NET 6+, you can configure the behavior in the initialization code. Here’s an example of making it ignore crashed background … Read more

C# – How to batch read with Threading.ChannelReader

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In a consumer/producer scenario, there are many reasons why you might want the consumer to read a batch of items. Maybe you’re bulk inserting into the database, or sending a payload with HttpClient. Sending lots of individual items over the network can be costly, and waiting for a full batch of items before sending is … Read more

C# – Async/await with a Func delegate

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To make a Func delegate awaitable, you have to make its out parameter a Task, like this: This Func accepts an int parameter and returns a Task. Since it returns a Task, it can be awaited. Notice that this isn’t returning a value. Normally you’d use an Action delegate if you didn’t want to return … Read more

C# – Handle a faulted Task’s exception

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When a Task throws an exception and stops running, it has faulted. The question is, how do you get the exception that was thrown from the faulted Task? This depends on if you’re awaiting the Task or not. This article shows how to handle a faulted Task’s exception in two scenarios: when you’re awaiting the … Read more

C# – Using Channel as an async queue

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The Channel class (from System.Threading.Channels) is a non-blocking async queue. It implements the producer-consumer pattern, which has two parts: Compare this with using BlockingCollection, which is a blocking concurrent queue. In this article, I’ll show how to use a Channel. 1 – Create the Channel The first step is to create the Channel object. Here’s … Read more

C# – Async Main

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The Async Main feature was added in C# 7.1 and works with all overloads of the Main() method. To make the Main() method async, add async Task to the method signature, like this: This is syntax sugar that compiles down to calling GetAwaiter().GetResult() on whatever you’re awaiting. In other words, it’s equivalent to doing the … Read more

C# – How to unit test async methods

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Let’s say you have the following async method you want to test: Here’s how to unit test this: This is awaiting the method you’re testing. To await it, you must make the unit test method return async Task. This example is a bit simplistic. In the real world when you are working with async methods, … Read more

C# – Fixing the Sync over Async antipattern

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The Sync over Async antipattern is when you’re using a blocking wait on an async method, instead of awaiting the results asynchronously. This wastes the thread, causes unresponsiveness (if called from the UI), and exposes you to potential deadlocks. There are two causes: In this article I’ll show an example of the Sync over Async … Read more

How to set a timeout for TcpClient.ConnectAsync()

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TcpClient has no direct way to set the connection timeout. It doesn’t have any parameters that allow you to control it, and SendTimeout / ReceiveTimeout don’t apply to the initial connection. The way I control the connection timeout is by awaiting a Task.WhenAny() with TcpClient.ConnectAsync() and Task.Delay(). Task.WhenAny() returns when any of the tasks complete. … Read more