Understanding Async/Await in C#: A Deep Dive

Introduction

• Speakers: Scott Hanselman and Steven Tobe
• Topic: Understanding the async/await pattern in C#
• Context: 12-13 years since async/await was introduced (around 2010).
• Goal: To explore the underlying implementation of async/await and improve programming skills.

Async/Await Overview

• Async and Await: Patterns extending beyond C#; have influenced numerous programming languages.
• Misconceptions: Despite its age, developers often misunderstand async/await due to its complexity.

Implementing Async/Await from Scratch

• Objective: Simulate a simple version of async/await to grasp its core concepts.
• Tools Used: Visual Studio, .NET, C#

Asynchrony vs. Concurrency

• Asynchrony: Launching a task that may not complete immediately, allowing other tasks to run concurrently.
• Concurrency: Multiple tasks running at the same time.
• Key Point: Asynchrony can exist without concurrency, but not vice versa.

Thread Pool Basics

• Thread Pool: A core component to support concurrency by managing multiple threads.
• Example: Implement a simple thread pool and explore its implications on concurrent execution.
• Challenge: Understanding variable scope and concurrent execution effects.

Execution Context and Async Local

• Execution Context: Mechanism for flowing thread state across asynchronous calls.
• Async Local: Allows data to be shared in the context of async operations without global/static state conflicts.

Task Implementation

• Task Class: Represents asynchronous operations and allows querying and waiting for completion.
• Features:
  • isCompleted: Check if a task is done.
  • setResult, setException: Mark task as completed successfully or with an error.
  • continueWith: Register a callback for task completion.
• Synchronization: Importance of thread-safe operations using locks and interlocks.

Building Higher-Level Constructs

• Task Extensions:
  • whenAll: Wait for multiple tasks to complete.
  • delay: Introduce an asynchronous delay without blocking threads.

Iterators and Async/Await

• Yield and Iterators: Analogies to understanding async patterns.
• Custom Iteration: Implementing an async-like iteration pattern.

Integrating Await with Custom Tasks

• Awaiter Pattern: Adapting custom tasks to support await using IAsyncResult.
• Syntactic Sugar: Making async code more readable and maintainable.

Conclusion

• Layer Understanding: Encouragement to understand the underlying mechanics of tools used.
• Benefits: Better usage in practical applications, even if not implementing from scratch.
• Engagement: Importance of continued learning and exploration of lower-level concepts.