practical_coroutines_23.kt

val ceh = CoroutineExceptionHandler { _, throwable ->
    launch (Dispatchers.Main) { showFailedUI() }
}
launch(Dispatchers.Default + ceh) {
    val apiCall1Result = async {
        val r1 = apiCall1()
        if(r1.status=="failed") {
            throw Exception("api call 1 fails")
        }
    }
    val apiCall2Result = async {
        val r2 = apiCall2()
        if(r2.status=="failed") {
            throw Exception("api call 2 fails")
        }
    }
    val combinedResult = apiCall1Result.await() + 
                                apiCall2Result.await()
    launch(Dispatchers.Main) { 
        showSuccessUI(combinedResult)
    }
}