Demo of Kotlin coroutine crash machinery

CoroutineCrashes.kt

import kotlinx.coroutines.CoroutineExceptionHandler
import kotlinx.coroutines.CoroutineScope
import kotlinx.coroutines.Job
import kotlinx.coroutines.SupervisorJob
import kotlinx.coroutines.async
import kotlinx.coroutines.delay
import kotlinx.coroutines.launch
import kotlinx.coroutines.runBlocking

fun main() =
    try {
        demo1JustCrash()
//        demo2JustCrash()
//        demo3JustCatch()
//        demo4AwaitCrashOrCancel()
//        demo5AwaitCrashOrCancel()
//        demo6AwaitHandleCrash()

        println()
        println("Your app finished successfully! 🎉")
    } catch (t: Throwable) {
        println()
        println("Your app crashed! 😰")
        println(t)
        println()
        println(
            """
            👾  👾   👾  👾
            👾 GAME OVER 👾
            👾  👾   👾  👾
        """.trimIndent()
        )
    }

suspend fun crash(): Any? {
    delay(500)
    throw Throwable("🔥")
}

fun handle(throwable: Throwable) = println("OK, handled: $throwable")

fun demo1JustCrash() {
    printDemo(1)

    val scope = CoroutineScope(Job())

    val job = scope.launch { crash() }

    // Ensure we don't continue before all coroutines complete
    runBlocking { job.join() }

    /* Where did the exception go? Who caught it? */
}

fun demo2JustCrash() {
    printDemo(2)

    val scope = CoroutineScope(Job())

    val deferred = scope.async { crash() }

    // Ensure we don't continue before all coroutines complete
    runBlocking { deferred.await() }

    /* Where did the exception go? Who caught it? */
}

fun demo3JustCatch() {
    printDemo(3)

    val scope = CoroutineScope(Job())

    val job = scope.launch {
        // Just catch inside your coroutine body
        try {
            crash()
        } catch (t: Throwable) {
            handle(t)
        }
    }

    val deferred = scope.async {
        // Just catch inside your coroutine body
        try {
            crash()
        } catch (t: Throwable) {
            handle(t)
        }
    }

    // Ensure we don't continue before all coroutines complete
    runBlocking {
        job.join()
        deferred.await()
    }
}

fun demo4AwaitCrashOrCancel() {
    printDemo(4)

    val parentJob = Job()
    val scope = CoroutineScope(parentJob)

    // Obtain a future value
    val deferred = scope.async { crash() }

    // Await it in another coroutine
    val awaitJob = scope.launch { deferred.await() }

    // Ensure we don't continue before all coroutines complete
    runBlocking { awaitJob.join() }

    /* Where did the exception go? Who caught it? */

    /* What will the following print? */
    println("isActive = ${parentJob.isActive}")
    println("isCancelled = ${parentJob.isCancelled}")
    println("isCompleted = ${parentJob.isCompleted}")
}

fun demo5AwaitCrashOrCancel() {
    printDemo(5)

    val parentJob = SupervisorJob()
    val scope = CoroutineScope(parentJob)

    // Obtain a future value
    val deferred = scope.async { crash() }

    // Await it in another coroutine
    val awaitJob = scope.launch { deferred.await() }

    // Ensure we don't continue before all coroutines complete
    runBlocking { awaitJob.join() }

    /* Where did the exception go? Who caught it? */

    /* What will the following print? */
    println("isActive = ${parentJob.isActive}")
    println("isCancelled = ${parentJob.isCancelled}")
    println("isCompleted = ${parentJob.isCompleted}")

    /* What will the following print? */
    println("isActive = ${awaitJob.isActive}")
    println("isCancelled = ${awaitJob.isCancelled}")
    println("isCompleted = ${awaitJob.isCompleted}")
}

fun demo6AwaitHandleCrash() {
    printDemo(6)

    val parentJob = SupervisorJob()
    val coroutineExceptionHandler = CoroutineExceptionHandler { _, exception ->
        println("Coroutine exception handler: $exception")
    }
    val scope = CoroutineScope(parentJob + coroutineExceptionHandler)

    // Obtain a future value
    val deferred = scope.async { crash() }

    // Await it in another coroutine
    val awaitJob = scope.launch { deferred.await() }

    // Ensure we don't continue before all coroutines complete
    runBlocking { awaitJob.join() }

    /* Where did the exception go? Who caught it? */

    /* What will the following print? */
    println("isActive = ${parentJob.isActive}")
    println("isCancelled = ${parentJob.isCancelled}")
    println("isCompleted = ${parentJob.isCompleted}")

    /* What will the following print? */
    println("isActive = ${awaitJob.isActive}")
    println("isCancelled = ${awaitJob.isCancelled}")
    println("isCompleted = ${awaitJob.isCompleted}")
}

private fun printDemo(n: Int) {
    println()
    println("Demo $n")
    println()
}