C# Exception Handling Best Practices

Previously I’ve written about exception handling best practices in .Net here and the best practices related to expectation handling in async cases here. But those post have a kind of long format which is not suitable for someone who is short on time. So, in this post I’m going to go through some of the best practices in that post, but I make it short this time. In other words this post is meant to take a short look at those best practices without going too much into details.

I’m going to separate each case where exception handling consideration might be different into its own section. Such as regular exception handling, exception handling when there async code involved etc.

General Exception Handling

1. Catch Specific Exceptions: Only catch exceptions you are expecting and can handle meaningfully.
2. Avoid Swallowing Exceptions: Never catch and suppress exceptions without handling them.
3. Proper Use of throw: Use throw instead of throw ex to preserve the original stack trace.
4. Logging: Log exceptions to provide more information about the cause of the problem.
5. Level of Abstraction: Handle exceptions at the right abstraction level, so higher-level code isn’t affected by lower-level exceptions.
6. Resource Management with try-catch-finally: Ensure resources are released properly, even if an exception occurs.
7. Use using Statement: Automatically dispose of resources even if an exception is thrown.
8. Custom Exceptions with ApplicationException: Create custom exceptions specific to your application.
9. Avoid Exceptions in Property Accessors: Exceptions in getters/setters can lead to unexpected behavior.
10. Exception Filters: Use them for more specific handling.
11. Avoid Exceptions for Control Flow: It makes code difficult to read and understand.
12. Meaningful Messages: Use Exception.Message for clear error messaging.
13. Stack Trace Logging: Utilize Exception.StackTrace for detailed error location.
14. Inner Exceptions: Use InnerException for underlying cause details.
15. Use of finally: Ensure resource release even when exceptions occur.
16. Avoid Exceptions for Expected Errors: Use return values or status codes for common issues.
17. Assertion in Development: Use Debug.Assert for conditions that must always be true.
18. Argument Validation: Use ArgumentNullException for null arguments, ArgumentException for invalid arguments, and ArgumentOutOfRangeException for arguments outside valid range.
19. State Validation: Use InvalidOperationException for invalid operation states.
20. Performance Consideration: Minimize exceptions in performance-critical sections.
21. Handling Multiple Exceptions: Use AggregateException for simultaneous exceptions.
22. Avoid Null Returns on Exceptions: It obscures error causes.
23. Immediate Termination for Critical Errors: Use Environment.FailFast. That will help conserving resources in cases when the precondition for the success of the operation is not met.
24. Precondition Validation in Methods: Connected to the previous case, we should make it a habit to validate the preconditions of our methods and terminate if each step if those preconditions are not met.

Exception Handling in Asynchronous Code

Async Exception Wrapping: Be aware that exceptions in async code are often wrapped in AggregateException.
Awaiting Tasks: When you await a Task, exceptions are re-thrown, so catch them as you would in synchronous code.
Handling Exceptions in Task Chains: When chaining tasks, handle exceptions in each task or at the end of the chain.
Catching Exceptions in Continuations: Use Task.ContinueWith with a continuation for handling exceptions.
Configuring Task Continuation for Exceptions: Use TaskContinuationOptions to fine-tune exception handling in task continuations.
Synchronization Context Awareness: Understand how the synchronization context affects exception handling in async code.
Avoid Blocking on Async Code: Using .Result or .Wait() can lead to deadlocks and obscure exceptions. Prefer await.

Exception Handling Additional Considerations

Centralized Exception Handling In applications with multiple layers, centralized exception handling simplifies error management by reducing redundant code and ensuring consistent handling strategies. For example, in ASP.NET Core, you can use middleware to catch exceptions from various parts of your application, log them, and return standardized error responses to the client. This approach not only declutters individual modules from repetitive try-catch blocks but also allows for more sophisticated error handling strategies like conditionally handling exceptions based on types or other criteria.
Exception Propagation Effective exception propagation involves deciding whether to handle an exception immediately or to allow it to bubble up to a higher level. In C#, this often means catching exceptions at a level where you can meaningfully react to them. For instance, a low-level method might throw an IOException, but it’s the higher-level method that knows whether to retry the operation, prompt the user, or abort the process. Propagating exceptions properly helps maintain clear separation of concerns and keeps the error-handling logic organized.
Custom Exception Classes Creating custom exception classes in C# is beneficial when you need to convey specific error information. Derive from System.Exception or a more specific exception subclass, and add relevant properties to carry additional data about the error. For instance, if you’re building an e-commerce application, a ProductNotFoundException with ProductId property can provide more context than a generic NotFoundException. Remember to mark your custom exceptions with the [Serializable] attribute for cross-boundary exception handling.
Retry Policies Implementing retry policies is crucial for handling transient failures in network operations or database connections. In C#, you might use the Polly library to define a retry policy with exponential backoff, which gradually increases the wait time between retries to reduce the load on the system. A circuit breaker pattern can also be used to temporarily halt operations when a certain threshold of failures is reached, preventing a cascade of failures in unstable system states.
Error Codes vs. Exception Types While exceptions are great for conveying error contexts, sometimes using error codes can be more practical, especially in API responses. In C#, you might define an ErrorCode enum and include it in your custom exceptions. This approach offers a clear, standardized way of indicating errors, which can be particularly useful in cross-language or cross-platform scenarios where exception details may not be easily interpretable.
Dependency Injection and Exception Handling Dependency injection (DI) frameworks in C# can be used to manage exception handling policies. For example, you can create a service to handle exceptions and register it with the DI container. This service can then be injected wherever needed, promoting reusability and separation of concerns. This approach is beneficial in large applications where you want to maintain consistent exception handling strategies across different modules.
Localized Error Messages For applications targeting a global audience, localizing error messages is essential. In C#, you can store error messages in resource files and use ResourceManager to retrieve the appropriate message based on the user’s locale. This ensures that error messages are understandable to users from different cultural and linguistic backgrounds, improving the overall user experience.
Exception Handling in Event Handlers In event-driven architectures, handling exceptions in asynchronous event handlers requires careful consideration. In C#, unhandled exceptions in event handlers can cause the application to crash. To prevent this, wrap the event handler code in a try-catch block and consider logging the exception or implementing a strategy to retry the operation, depending on the application’s requirements.
Testing Exception Handling Testing exception handling in C# can be achieved using unit testing frameworks like NUnit or xUnit. You can write tests that intentionally trigger exceptions to ensure that your code handles them correctly. For example, if you have a method that throws an ArgumentException for invalid input, your test should assert that this exception is thrown as expected under those conditions. Mocking frameworks like Moq can be used to simulate exceptional scenarios in dependent services or components.
Fail-Safe Mechanisms Implementing fail-safe mechanisms is crucial in systems where continuity is critical. In C#, consider using try-catch blocks at the top level of your application to catch any unhandled exceptions and perform necessary cleanup or state preservation operations before shutting down. Additionally, you might implement a watchdog timer that restarts the application if it becomes unresponsive due to an unrecoverable error.
Exception Handling and Clean Code Practices Integrating exception handling with clean code practices in C# involves writing clear, maintainable, and self-documenting exception handling code. Avoid complex try-catch blocks or nested exception handling that can make the code hard to read and maintain. Use meaningful exception names and error messages, and consider creating separate methods or classes for handling specific types of exceptions to keep your code organized and readable.
Exception Handling in Different Programming Paradigms Exception handling varies across programming paradigms. In C#’s object-oriented programming (OOP), exceptions are typically handled using try-catch blocks. In contrast, functional programming paradigms might use monadic error handling (like Option or Either types) to represent errors as first-class citizens without throwing exceptions. Understanding these differences is crucial when working in a multi-paradigm language like C#.
Versioning and Exceptions Handling exceptions across different versions of an API or library in C# requires careful planning to maintain backward compatibility. Avoid changing the exceptions thrown by a method in a way that would surprise existing clients. If a new version of a method needs to throw additional exceptions, consider creating a new version of the method or API endpoint, leaving the old one intact for backward compatibility.
Impact on Application Performance Exception handling can impact application performance in C#. Throwing and catching exceptions is relatively expensive in terms of system resources. Therefore, use exceptions judiciously, particularly in performance-critical sections of your application. Prefer validation and error-checking mechanisms to avoid exceptions as part of the normal control flow.

Other Distinct Cases About Exception Handling

Concurrency Exceptions: In multi-threaded environments, handle race conditions and synchronization issues carefully.
I/O Exceptions: Differentiate between recoverable and non-recoverable I/O errors, handling each appropriately.
Security Exceptions: Be cautious with information revealed in exceptions to avoid security vulnerabilities.
Database Exceptions: Handle database-specific exceptions like connection failures or query errors distinctly.
Network Exceptions: For network operations, handle timeouts, connection failures, and protocol errors appropriately.
Third-party Library Exceptions: Understand and handle exceptions thrown by external libraries or frameworks.

Various Other Exception Handling Best Practices

Consistent Strategy: Apply a consistent exception handling strategy across your application.
Documentation: Document your exception handling policies and the rationale behind them.
Testing: Include exception scenarios in your testing processes to ensure robustness.
User-Friendly Error Reporting: When showing errors to users, make them understandable and not intimidating. Avoid exposing technical details.
Monitoring and Alerting: Implement monitoring for exceptions to detect and address issues proactively.

Hamid Mosalla

Programming Adventures