Async Programming with async/await

55 min

async/await pattern simplifies asynchronous programming, enabling you to write asynchronous code that looks synchronous. async/await eliminates callback hell and makes asynchronous code readable. Async methods don't block threads, enabling better resource utilization. Understanding async/await enables responsive applications. async/await is essential for modern C#.

Async methods return Task (void-like) or Task<T> (returns T), representing ongoing asynchronous operations. Task represents a single operation. Task<T> represents an operation that returns a value. Tasks can be awaited, chained, and composed. Understanding Task types enables effective async programming. Tasks are the foundation of async/await.

await keyword pauses execution until the awaited task completes, without blocking the thread. await unwraps Task<T> to T. The method returns control to the caller while waiting. When the task completes, execution resumes. Understanding await enables non-blocking async code. await is the key to async/await.

Async programming is essential for I/O operations (file, network, database) and web requests, enabling applications to remain responsive during long-running operations. I/O operations are naturally asynchronous. Using async/await for I/O prevents thread blocking. Understanding async I/O enables scalable applications. Async I/O is critical for performance.

Best practices include using async/await for I/O operations, avoiding async void (use async Task), using ConfigureAwait(false) in library code, not blocking on async code (use await), and understanding that async doesn't mean parallel. Understanding best practices enables effective async code. Async programming requires understanding its behavior.

Best practices include using async/await for all I/O operations, returning Task/Task<T> from async methods, avoiding async void except for event handlers, using ConfigureAwait(false) in library code, and not mixing async and blocking code. Understanding async/await enables responsive, scalable applications. Async programming is essential for modern applications.

Key Concepts

async/await pattern simplifies asynchronous programming.
Async methods return Task or Task<T>.
await keyword pauses execution without blocking threads.
Async programming is essential for I/O operations.
Tasks represent ongoing asynchronous operations.

Learning Objectives

Master

Creating async methods with async/await
Understanding Task and Task<T> return types
Using await for non-blocking operations
Handling async exceptions and cancellation

Develop

Understanding asynchronous programming concepts
Designing responsive, scalable applications
Appreciating async/await's role in modern C#

Tips

Use async/await for all I/O operations (file, network, database).
Return Task or Task<T> from async methods, not void.
Use await instead of .Result or .Wait() to avoid deadlocks.
Use ConfigureAwait(false) in library code to avoid context capture.

Common Pitfalls

Using async void, making exceptions unhandled.
Blocking on async code with .Result or .Wait(), causing deadlocks.
Not using async/await for I/O, blocking threads unnecessarily.
Not understanding that async doesn't mean parallel.

Summary

async/await simplifies asynchronous programming.
Async methods return Task or Task<T>.
await pauses execution without blocking threads.
Async programming is essential for I/O operations.
Understanding async/await enables responsive applications.

Exercise

Create async methods to simulate web requests and file operations.

using System;
using System.Threading.Tasks;

class Program
{
    // Simulate a web request
    static async Task<string> FetchDataAsync(string url)
    {
        Console.WriteLine($"Starting request to {url}...");
        await Task.Delay(2000); // Simulate network delay
        return $"Data from {url}";
    }
    
    // Simulate file reading
    static async Task<string> ReadFileAsync(string filename)
    {
        Console.WriteLine($"Reading file {filename}...");
        await Task.Delay(1000); // Simulate file I/O
        return $"Content of {filename}";
    }
    
    static async Task Main(string[] args)
    {
        Console.WriteLine("Starting async operations...");
        
        // Sequential execution
        var data1 = await FetchDataAsync("https://api.example.com/data1");
        var data2 = await FetchDataAsync("https://api.example.com/data2");
        
        Console.WriteLine(data1);
        Console.WriteLine(data2);
        
        // Parallel execution
        Console.WriteLine("\nStarting parallel operations...");
        var task1 = FetchDataAsync("https://api.example.com/parallel1");
        var task2 = FetchDataAsync("https://api.example.com/parallel2");
        var task3 = ReadFileAsync("config.txt");
        
        // Wait for all tasks to complete
        await Task.WhenAll(task1, task2, task3);
        
        Console.WriteLine("All operations completed!");
    }
}

Async Programming with async/await