Exception handling in async code in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of exception handling in async code?

Exception handling in async code helps catch and manage errors that happen during asynchronous operations, preventing the program from crashing and allowing graceful recovery.

beginner

How do you catch exceptions from an async method in C#?

You use a try-catch block around the await call to the async method. If the async method throws an exception, it will be caught in the catch block.

intermediate

What happens if you don't await an async method and it throws an exception?

If you don't await the async method, exceptions may go unobserved and can cause the program to crash later or behave unpredictably.

intermediate

Explain how to handle multiple exceptions from multiple awaited async calls.

You can use multiple try-catch blocks for each awaited call or use a single try-catch around all awaits. To handle multiple exceptions together, use Task.WhenAll and catch exceptions from the awaited task, which are wrapped in an AggregateException.

advanced

What is the role of AggregateException in async exception handling?

AggregateException groups multiple exceptions thrown by tasks running in parallel. When awaiting Task.WhenAll, exceptions are wrapped in AggregateException to handle them together.

Which keyword is used to wait for an async method to complete and catch exceptions it throws?

A await

B async

C try

D catch

The 'await' keyword waits for the async method to finish and allows exceptions to be caught in the surrounding try-catch.

What happens if you call an async method without awaiting it and it throws an exception?

A Program automatically retries the async method

B Exception is ignored and program continues safely

C Exception is caught immediately

D Exception may go unobserved and cause issues later

Without awaiting, exceptions may not be observed immediately and can cause crashes or unexpected behavior later.

How can you handle exceptions from multiple async tasks running in parallel?

A Use multiple try-catch blocks separately

B Ignore exceptions from parallel tasks

C Use Task.WhenAll and catch AggregateException

D Use async void methods

Task.WhenAll waits for all tasks and throws an AggregateException containing all exceptions, which you can catch and handle.

Which of these is NOT a good practice for exception handling in async code?

A Ignore exceptions from async methods

B Use try-catch around awaited calls

C Always await async methods

D Handle AggregateException when using Task.WhenAll

Ignoring exceptions can cause hidden bugs and crashes; always handle exceptions properly.

What type of exception wraps multiple exceptions from parallel async tasks?

A InvalidOperationException

B AggregateException

C NullReferenceException

D TimeoutException

AggregateException groups multiple exceptions thrown by parallel tasks.

Describe how you would catch and handle exceptions from an async method in C#.

Think about how you wait for the async method and where you put the try-catch.

Explain the role of AggregateException when working with multiple async tasks.

Consider what happens when many tasks fail at once.