Await vs. ContinueWith in Asynchronous Programming: Making the Right Choice

Introduction

Asynchronous programming has become essential to modern software development, allowing applications to perform tasks efficiently without blocking the main thread. In C#, developers have access to powerful tools like await and ContinueWith to handle asynchronous operations. So what is ‘await vs. ContinueWith?

While both can be used to manage asynchronous workflows, it’s crucial to understand why you should favour await over ContinueWith.

In this blog post, we will explore the reasons behind this choice and provide insights into the best practices of asynchronous programming.

The Role of await and ContinueWith

Before delving into the reasons to prefer await, let’s briefly understand both await and ContinueWith:

await:

• await is a keyword in C# used within an async method to pause execution until a specified asynchronous operation is complete.
  
• It is designed to improve the readability and maintainability of asynchronous code by making it appear more like synchronous code.
  
• It automatically captures the current synchronisation context, ensuring that the continuation runs on the original context (e.g., UI thread in GUI applications) when necessary.

ContinueWith:

• ContinueWith is a method available on tasks that allows you to specify an action to be executed when the task is completed.
  
• It provides more explicit control over the flow of execution, enabling you to define custom continuation logic.
  
• However, it doesn’t capture the synchronisation context by default, potentially leading to issues when trying to update UI elements in GUI applications.

Reasons to Use await vs. ContinueWith

Now, let’s explore why await is generally preferred over ContinueWith in asynchronous programming:

1. Improved Readability and Maintainability:

• await makes asynchronous code more readable and resembles synchronous code, making it easier to understand and maintain.
  
• It reduces the need for explicit handling of task continuations, resulting in cleaner and less error-prone code.

2. Exception Handling:

• await handles exceptions more naturally. Exceptions thrown by the awaited task are automatically propagated to the calling method.
  
• In contrast, with ContinueWith, you need to explicitly check for exceptions using the Task.Exception property, making error handling less intuitive.

3. Synchronisation Context:

• await captures and respects the synchronisation context by default. This is crucial in GUI applications to ensure that UI updates occur on the UI thread.
  
• With ContinueWith, you must manually capture the synchronisation context using TaskScheduler.FromCurrentSynchronizationContext(), which can be error-prone and lead to subtle bugs.

4. Avoiding Task Continuation Chains:

• await allows you to create a linear flow of asynchronous code without nesting or chaining multiple ContinueWith calls.
  
• Chained ContinueWith calls can make code harder to read and maintain due to increased nesting levels.

5. Better Integration with async/await:

• await integrates seamlessly with other async/await code, creating a cohesive and consistent asynchronous programming model.
  
• Mixing await with ContinueWith can result in a less cohesive and more complex codebase.

When to Consider ContinueWith

While await is the preferred choice in most asynchronous programming scenarios, there are cases where ContinueWith may be useful:

• When you need fine-grained control over task continuations, such as executing multiple tasks concurrently and aggregating their results.
  
• When you have specific requirements for handling exceptions or controlling task scheduling.
  
• In advanced scenarios where await may not provide the desired level of control.

Conclusion

await is the recommended choice for most asynchronous programming scenarios due to its improved readability, exception handling, and built-in synchronisation context management.

By favouring await, you can write cleaner, more maintainable, and more reliable asynchronous code, enhancing the overall quality of your applications.

While ContinueWith has its place in specific situations, it should be used judiciously and with a clear understanding of its implications.

There is a good write-up about continuewith here: – https://learn.microsoft.com/en-us/dotnet/standard/parallel-programming/chaining-tasks-by-using-continuation-tasks

I have written a number of other posts on asynchronous programming here: – Understanding Task.Yield, Asynchronous Task.Delay.