Async in C# 5.0

Preface

Async is a powerful feature added to the C# programming language in C# 5.0. It comes at a time when performance and parallelization are becoming a major concern of software developers. Used correctly, it can help to write programs with performance and parallelization properties that would have needed reams of code without it. However, what it does to your program is complex, and there are plenty of aspects to how it works that aren’t immediately obvious.

Excepting Visual Basic .NET, which added async at the same time as C#, no other mainstream programming languages offer capabilities equivalent to async. Experience and guidance in using it in real-world programs is rare. This book is the guidance from my experience using async, as well as ideas drawn from the designers of C# and computer science theory. More importantly, it shows what async is, how it works, and why you might want to use it.

Intended Audience

This book is intended for people who are already confident C# programmers. Perhaps you are looking to understand async, to choose whether to start using it. Perhaps you have already started using async, but need to learn advanced techniques and caveats to make best use of it.

Having said that, it doesn’t assume knowledge of other advanced C# features, so the book is approachable to C# beginners, as well as programmers confident in other languages.

C# is used in many kinds of application, and async is useful for different reasons in each of these. For that reason, this book looks at async from both client and server points of view, including chapters specifically for ASP.NET and WinRT.

How to Read This Book

This book is primarily designed to be read from beginning to end, as a way to learn about async. It introduces concepts in order, helping you to understand with examples before relying on that understanding. This is especially true of the first five chapters of the book.

The best way to learn is by doing, so I recommend that you try out code examples yourself. For this, you’ll need a C# development environment, like Microsoft Visual Studio or MonoDevelop. Take opportunities to extend the examples and work on your own programs while reading, to understand the ideas fully.

After reading the book, you may want to go back and use the sixth chapter onwards as a reference for advanced topics in the use of the async. These chapters are organized into self-contained topics.

• Chapters 6 and 7 focus on techniques to use in async code

• Chapters 8 and 9 focus on complex behaviors of async

• Chapters 10 to 13 discuss situations where async is useful

• Chapters 14 and 15 look at how async works internally

Conventions Used in This Book

The following typographical conventions are used in this book:

Italic

Indicates new terms, URLs, email addresses, filenames, and file extensions.

Constant width

Used for program listings, as well as within paragraphs to refer to program elements such as variable or function names, databases, data types, environment variables, statements, and keywords.

Constant width italic

Shows text that should be replaced with user-supplied values or by values determined by context.

Note

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Using Code Examples

This book is here to help you get your job done. In general, you may use the code in this book in your programs and documentation. You do not need to contact us for permission unless you’re reproducing a significant portion of the code. For example, writing a program that uses several chunks of code from this book does not require permission. Selling or distributing a CD-ROM of examples from O’Reilly books does require permission. Answering a question by citing this book and quoting example code does not require permission. Incorporating a significant amount of example code from this book into your product’s documentation does require permission.

We appreciate, but do not require, attribution. An attribution usually includes the title, author, publisher, and ISBN. For example: “Async in C# 5.0 by Alex Davies (O’Reilly). Copyright 2012 Alex Davies, 978-1-449-33716-2.”

If you feel your use of code examples falls outside fair use or the permission given above, feel free to contact us at [e-mail].

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Acknowledgments

I’d like to thank Stephen Toub for reviewing the book, not just technically, but lending me his experience in getting across parallel computing concepts. His blog was also the first place I saw a lot of the ideas I’ve explained here. Thank you to Hamish for proof-reading, and to Katie for bringing me tea while writing.

Thanks also to Rachel Roumeliotis, my editor, and the team at O’Reilly who have been very helpful while I’ve been writing.

I thank my family, especially my Mum, who looked after me during the recovery from surgery in which most of the book was written. Finally, I’d like to thank my colleagues at Red Gate, who encouraged the atmosphere of experimentation that led me to learn about async at work.