Calling Asynchronous Methods from Synchronous Methods in C#

Asynchronous programming is a powerful tool for writing efficient and scalable code, but it can be challenging to integrate with existing synchronous codebases. In this tutorial, we will explore how to call asynchronous methods from synchronous methods in C#.

First, let’s consider the basics of asynchronous programming in C#. When you use the async keyword to define a method, you are indicating that the method contains asynchronous operations. The await keyword is used to suspend the execution of the method until the asynchronous operation completes.

However, when you need to call an asynchronous method from a synchronous method, things can get complicated. The problem arises because synchronous methods cannot use the await keyword, which means they cannot wait for the completion of an asynchronous operation without blocking the thread.

To address this issue, we will explore three different solutions:

Solution A: Using Task.WaitAndUnwrapException

One way to call an asynchronous method from a synchronous method is by using the Task.WaitAndUnwrapException method. This approach is suitable when the asynchronous method does not need to synchronize back to its context.

var task = MyAsyncMethod();
var result = task.WaitAndUnwrapException();

However, this solution has some limitations. The asynchronous method should not use await without ConfigureAwait(false), as this can cause a deadlock in certain situations.

Solution B: Using AsyncContext.RunTask

Another approach is to use the AsyncContext.RunTask method from the Nito.AsyncEx library. This method provides a nested context for the asynchronous operation, which allows it to complete without deadlocking.

var result = AsyncContext.RunTask(MyAsyncMethod).Result;

This solution is more robust than Solution A but requires the use of an external library.

Solution C: Using Task.Run

A third approach is to use Task.Run to start the asynchronous method on a background thread. This allows the synchronous method to continue executing without blocking.

var task = Task.Run(async () => await MyAsyncMethod());
var result = task.WaitAndUnwrapException();

However, this solution requires that the asynchronous method is designed to work in a thread pool context and does not attempt to access UI elements or the ASP.NET request context.

Best Practices

When calling asynchronous methods from synchronous methods, it’s essential to follow best practices to avoid deadlocks and ensure efficient execution. Here are some tips:

• Use ConfigureAwait(false) whenever possible to prevent deadlocks.
• Avoid using Task.Wait or Task.Result without WaitAndUnwrapException, as this can wrap exceptions in an AggregateException.
• Consider using external libraries like Nito.AsyncEx to provide a nested context for asynchronous operations.

By following these guidelines and choosing the right solution for your specific use case, you can effectively call asynchronous methods from synchronous methods in C#.