The launch function returns an instance of the Job class, which means that a coroutine can be cancelled at any time. In this case, if we have a long-term operation in the finally block, JobCancellationException will be thrown.

The following example shows a case like this:

fun main(args: Array<String>) = runBlocking<Unit> {
    val job = launch {
        try {
            delay(1000000)
        } finally {
            try {
                println("start")
                delay(1000)
                println("end")
            } catch (exception: Exception) {
                exception.printStackTrace()
            }
        }
    }
    delay(500)
    job.cancel()
    job.join()
}

The following is the output:

kotlinx.coroutines.experimental.JobCancellationException: Job was cancelled normally; job=StandaloneCoroutine{Cancelling}@7f77b211
 start

As you can see, the finally block can't be executed in a canceled coroutine and we can't release resources. We can deal with this using the withContext function:

withContext(NonCancellable) {
    try {
        println("start")
        delay(1000)
        println("end")
    } catch (exception: Exception) {
        exception.printStackTrace()
    }
}

start
end

The withContext function invokes the passed suspended block with a given coroutine context.