Kotlin Coroutines Exception Handling Cheat Sheet

Exception Handling with Kotlin Coroutines is hard. I wrote an extensive article about it and gave talks about it at several conferences. Some developers suggested creating some kind of cheat sheet that could be helpful for implementing appropriate exception handling in coroutine-based code. Here it is 😉. It contains the six most important points. You can either download the PDF or read this article.

You can watch an even more comprehensive video about Exception Handling in Kotlin Coroutines here !

1) Exceptions can be handled directly in a Coroutine with a try-catch block. This way, the Coroutine doesn’t complete exceptionally.

2) If an exception is thrown in a Coroutine and not handled directly within the Coroutine with a try-catch block, the Coroutine completes exceptionally.

3) As a result, the exception is propagated up the job hierarchy until it reaches either the RootScope or a SupervisorJob. While the exception travels upwards, parent coroutines fail too and sibling coroutines get canceled. 

4) When the root coroutine was started with launch{}, the exception will be passed to an installed CoroutineExceptionHandler. 

When the root coroutine was started with async{}, the exception is encapsulated in the Deferred object.

5) The scoping function coroutineScope{} re-throws uncaught exceptions of its child Coroutines and so we can handle them with try/catch.

6) Keep in mind: 

  • When your Coroutine is not completing exceptionally, parent and sibling coroutines won’t be canceled. 
  • Suspend functions can throw a CancellationException at any point and by catching them, the Coroutine will keep on running.

Btw: I also cover exception handling in great detail in my course “Mastering Kotlin Coroutines for Android Development”.

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Lukas Lechner

I'm a Freelance Android Developer and Online Course Creator. I have many years of professional experience as an Android Developer and worked on some of the biggest mobile apps projects here in Austria. I like to write articles for my blog and speak at meetups and conferences.