Challenge 3: Cancelling a Running Coroutine — Solution

import kotlinx.coroutines.*

fun main() = runBlocking {
    var count = 0
    val job = launch {
        while (isActive) {
            println("Count: ${count++}")
            delay(300)
        }
    }

    delay(1500)
    job.cancel()
    println("Cancelled")
}

/*
Output:
Count: 0
Count: 1
Count: 2
Count: 3
Count: 4
Cancelled

Notes:
- Expect roughly 5 prints (0 through 4) before cancellation: with a
  300ms delay per iteration and cancelling after 1500ms, that's
  1500 / 300 = 5 iterations that get to start before job.cancel() takes
  effect (exact count can vary slightly depending on timing).
- while (isActive) checks whether the coroutine has been cancelled at
  the top of each loop iteration, so the loop stops cleanly on the next
  check after cancel() is called.
- delay(300) inside the loop also independently checks for cancellation
  and would throw a CancellationException if the coroutine were
  cancelled while it was suspended there — so the loop would stop even
  without the explicit isActive check, just less predictably as to
  exactly where.
*/