Why Should You Avoid Async Void Methods in C#?

Why Async Void Isn't a Great Idea: Breaking Down the Reasons

While returning void from an async method may seem harmless in certain situations, industry best practices strongly discourage it. Here's why:

1. Exception Handling Oddities

Async void methods have unique error-handling semantics. Exceptions that escape from the async void method, such as "PrimeCustomTask" in the provided example, become awkward to catch and handle. This complicates error handling and makes debugging more challenging.

2. Compositional Challenges

Async void methods lack the ability to compose well with other async operations. The code within "PrimeCustomTask" exists in isolation and cannot be easily integrated into higher-level async constructs. This limits code maintainability and code reuse.

3. Testing Difficulties

Unit testing async void methods is notoriously difficult. Since the method returns void, it's challenging to create reliable assertions and test all possible execution paths. This makes it difficult to ensure the correctness of the code.

4. Exception Propagation

As noted in the answer, exceptions escaping from "PrimeCustomTask" are not propagated naturally to its callers. This can lead to unexpected behavior and make it difficult to handle errors effectively.

Modifying to Follow Conventions

To align with established conventions, you can modify the code in the example to use async Task methods:

protected override async Task OnLoad(EventArgs e)
{
  if (CustomTask == null)
    await PrimeCustomTask();
}

private async Task PrimeCustomTask()
...

By returning async Task, you benefit from:

• Clear and consistent exception handling
• Improved code composition and reusability
• Easier unit testing
• Natural exception propagation

By embracing these best practices, you'll write more maintainable, testable, and reliable code when utilizing async methods.

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