Reference

  • It’s easier to understand if you think of a thread’s interrupt as a job’s cancel.
  • When using runCatching, you must write code to rethrow the CancellationException. Kotlin does not provide a convenience method for this. - Related Issue

Reason

When a job is cancelled, it should not continue running. However, if you catch a CancellationException, the job may continue to run, so it is recommended to rethrow it.

Problematic Code

If you do not rethrow, a job that is already cancelled may continue to run.

problem-code

For example, launch { testTask() } continues to run even after its state has changed to cancelled, so both apiCall Start and CancellationException are printed in sequence.

Correct Code

Therefore, if the job is finished, no more code should be executed, so you must throw a CancellationException to end code execution.

correct-code

The principle is simple. If a function throws an exception, it will not execute any further.

Reference

Kotlin Deep Dive - It is recommended to rethrow CancellationException.

deep-dive

Code Example - Coroutine Deep Dive

https://github.com/MarcinMoskala/kotlin-coroutines-recipes/blob/master/src/commonMain/kotlin/retryWhen.kt#L19-L21

code-example