Can you explain what a CancellationException is and in what situations it is used?

CancellationException is a special exception in Kotlin Coroutines that signals that a coroutine has been canceled. It is used to manage the cancellation of asynchronous tasks and is usually not considered an error, but a normal way to interrupt execution.

When the coroutine's cancel method (cancel()) is called, a CancellationException is thrown inside it, allowing to stop execution and free resources. Handling this exception allows for proper task completion and avoiding leaks.

Example of usage:

val job = CoroutineScope(Dispatchers.Default).launch {
    try {
        // Long operation
        delay(10000)
    } catch (e: CancellationException) {
        println("Coroutine was canceled")
        throw e // it is important to rethrow the exception
    }
}

// Cancel the coroutine
job.cancel()

Thus, CancellationException is a mechanism that helps manage the lifecycle of coroutines and respond correctly to their cancellation.