Asynchronous programming is a powerful feature in ASP.NET Core that allows you to perform non-blocking operations, improving the scalability and responsiveness of your applications. By using asynchronous calls, you can free up threads to handle other requests while waiting for I/O operations, such as database queries or web service calls, to complete. This guide will explain how to handle asynchronous calls in ASP.NET Core, including the use of async and await keywords.

1. Understanding Asynchronous Programming

Asynchronous programming allows you to write code that can perform tasks in the background without blocking the main thread. In ASP.NET Core, this is particularly useful for I/O-bound operations, such as:

• Database queries
• File I/O operations
• HTTP requests to external services

By using asynchronous methods, you can improve the throughput of your application, allowing it to handle more concurrent requests.

2. Using async and await

In C#, you can define asynchronous methods using the async modifier. Inside these methods, you can use the await keyword to call other asynchronous methods. This allows the method to pause execution until the awaited task is complete, without blocking the thread.

Sample Code for Asynchronous Controller Action

        
            using Microsoft.AspNetCore.Mvc;
            using System.Collections.Generic;
            using System.Threading.Tasks;

            [ApiController]
            [Route("api/[controller]")]
            public class ProductsController : ControllerBase
            {
                private readonly IProductService _productService;

                public ProductsController(IProductService productService)
                {
                    _productService = productService;
                }

                [HttpGet]
                public async Task<ActionResult<IEnumerable<Product>>> GetProducts()
                {
                    var products = await _productService.GetProductsAsync();
                    return Ok(products);
                }
            }
            

In this example, the GetProducts action method is defined as asynchronous. It calls the GetProductsAsync method of the IProductService interface, which is expected to return a list of products asynchronously.

3. Implementing Asynchronous Methods in Services

To implement asynchronous behavior in your services, you can use asynchronous methods provided by libraries such as Entity Framework Core or HttpClient. Below is an example of an asynchronous method in a service that retrieves products from a database.

Sample Code for Asynchronous Service Method

        
            using System.Collections.Generic;
            using System.Threading.Tasks;
            using Microsoft.EntityFrameworkCore;

            public class ProductService : IProductService
            {
                private readonly MyDbContext _context;

                public ProductService(MyDbContext context)
                {
                    _context = context;
                }

                public async Task<IEnumerable<Product>> GetProductsAsync()
                {
                    return await _context.Products.ToListAsync();
                }
            }
            

In this example, the GetProductsAsync method uses Entity Framework Core's ToListAsync method to retrieve products from the database asynchronously.

4. Handling Exceptions in Asynchronous Methods

When working with asynchronous methods, it's important to handle exceptions properly. You can use try-catch blocks to catch exceptions that may occur during the execution of asynchronous calls.

Sample Code for Exception Handling

        
            [HttpGet("{id}")]
            public async Task<ActionResult<Product>> GetProduct(int id)
            {
                try
                {
                    var product = await _productService.GetProductByIdAsync(id);
                    if (product == null)
                    {
                        return NotFound();
                    }
                    return Ok(product);
                }
                catch (Exception ex)
                {
                    // Log the exception (not shown here)
                    return StatusCode(500, "Internal server error");
                }
            }
            

In this example, the GetProduct action method includes a try-catch block to handle any exceptions that may occur when retrieving a product by its ID.

5. Asynchronous Programming Best Practices

When working with asynchronous programming in ASP.NET Core, consider the following best practices:

• Use async all the way: If you start using asynchronous methods, try to make all layers of your application asynchronous, including controllers, services, and data access.
• Avoid blocking calls: Do not use blocking calls like .Result or .Wait() on asynchronous methods, as this can lead to deadlocks and performance issues.
• Return Task<IActionResult>: In your controller actions, return Task<IActionResult> instead of IActionResult to ensure the action is asynchronous.
• Use ConfigureAwait(false): When awaiting tasks in library code, consider using ConfigureAwait(false) to avoid capturing the synchronization context, which can improve performance.

6. Conclusion

Handling asynchronous calls in ASP.NET Core is essential for building scalable and responsive applications. By utilizing the async and await keywords, developers can perform non-blocking operations that enhance the user experience. The examples provided illustrate how to implement asynchronous methods in controllers and services effectively, along with best practices to follow for optimal performance.