Brad Wilson

Task Parallel Library and Servers, Part 4: TaskHelpers

This is part 4 in a series on using Task Parallel Library when writing server applications, especially ASP.NET MVC and ASP.NET Web API applications.

1. Introduction
2. SynchronizationContext
3. ContinueWith
4. TaskHelpers

Simple Task Helpers

I know we left off in part 3 with a problem, but we're not going to solve it yet, because we still need to build some foundation helper classes that will make it easier to do that. In particular, there are some good practices we can codify around the creation and conversion of tasks that led us to write the TaskHelpers class that we use today in ASP.NET Web Stack.

Task Parallel Library and Servers, Part 3: ContinueWith

This is part 3 in a series on using Task Parallel Library when writing server applications, especially ASP.NET MVC and ASP.NET Web API applications.

1. Introduction
2. SynchronizationContext
3. ContinueWith
4. TaskHelpers

What ContinueWith Really Does

I promised that we had a bug in our previous code, and we did... sort of. Calling ContinueWith without any special flags will cause your continuation to always run, regardless of the final state of the task. We wrote our continuation under the assumption that the Task had completed successfully, which can lead to some very odd and hard to debug problems. Luckily, in our code, we ended up calling Result on the Task object, which turns around and throws an exception if the task had ended in a faulted or canceled state. But what if we'd had a Task rather than a Task<T>? Or what if we hadn't called Result? In .NET 4, this is considered a fatal error condition, and when the task object got garbage collected, its finalizer would've thrown an exception that takes down your AppDomain because you had an unobserved fault! Definitely not good.

Task Parallel Library and Servers, Part 2: SynchronizationContext

This is part 2 in a series on using Task Parallel Library when writing server applications, especially ASP.NET MVC and ASP.NET Web API applications.

1. Introduction
2. SynchronizationContext
3. ContinueWith
4. TaskHelpers

Introduction to SynchronizationContext

An important part of the work in properly handling tasks on the server is supporting the synchronization context. When you’re using .NET 4.5, then the await keyword automatically does this for you. When you’re consuming Task objects on .NET 4, though, getting yourself back onto the right synchronization context is critical; otherwise, you may cause errors in your application when trying to access things which touch the HttpContext in ASP.NET.

Task Parallel Library and Servers, Part 1: Introduction

This is part 1 in a series on using Task Parallel Library when writing server applications, especially ASP.NET MVC and ASP.NET Web API applications.

1. Introduction
2. SynchronizationContext
3. ContinueWith
4. TaskHelpers

Okay, let’s just get this out of the way:

Asynchronous (multi-threaded) programming is not easy.

This warning really has nothing to do with .NET in particular, because it can be quite challenging to do correctly on any framework, but here’s the good news:

Asynchronous programming with .NET 4 is a little easier.
Asynchronous programming with .NET 4.5 is a lot easier.