Concurrency in C# (.NET): Asynchrony, Parallelism, and Multithreading

Modern applications must be fast and responsive. Users do not tolerate freezes, and server systems must handle thousands of requests simultaneously. The book "Concurrency in C# (.NET)" is a comprehensive guide to all aspects of parallel and asynchronous programming on the .NET platform, which will help you transition from sequential code to high-performance concurrent solutions.

What is this book about?

The book is structured from simple to complex and covers all key topics:

• Basics of Multithreading: what threads, thread pools are, and how to work with them in .NET.
• Asynchronous Programming: a deep dive into the async/await pattern, Task and ValueTask, and synchronization context management.
• Task Parallel Library (TPL): parallel loops, tasks, the Parallel class, and efficient data processing.
• Synchronization and Locking: monitors, mutexes, semaphores, ReaderWriterLockSlim, and lock-free approaches.
• Thread-Safe Collections: ConcurrentDictionary, ConcurrentQueue, BlockingCollection, and Channels.
• Error Handling and Debugging: how to catch exceptions in asynchronous code, avoid deadlocks and race conditions.
• Reactive Programming: an introduction to Rx.NET and working with event streams.
• Advanced Techniques: Dataflow (TplDataflow), IAsyncEnumerable, parallelism with Span and Memory.

Who is this book for?

The book will be useful for:

• C# Developers who want to understand how to write asynchronous code without errors and leaks.
• Software Architects designing high-load systems on .NET.
• Tech Leads who want to implement best practices of concurrency in their teams.
• Students and Juniors who want to master one of the most complex topics in programming.

Reading requires a solid knowledge of C# syntax and a basic understanding of how the operating system works.

What will you learn?

• How to correctly use async/await to avoid blocking the UI and killing server performance.
• How to parallelize computations on multi-core processors using TPL.
• How to safely share data between threads without the risk of races and deadlocks.
• How to test and debug multithreaded code.
• How to build data processing pipelines using TPL Dataflow.
• How to avoid common antipatterns (e.g., "sync over async").

All code examples are relevant for .NET 8 and later versions, including .NET 9. The book contains many practical exercises and ready-made solutions that can be immediately applied in real projects. Whether you are writing a desktop application in WPF, a web service in ASP.NET Core, or a cloud function on Azure, the knowledge from this book will help you make your code faster, more stable, and more scalable.