Hi. I have an issue with

async

,

coroutineScope

and exception handling. When

coroutineScope

is moved into separate function, I am able to catch exception inside coroutine. When

coroutineScope

is declared inside coroutine, I am not able to catch exception. This code works fine:

suspend fun doWork(): Deferred<String> = coroutineScope {
        async(<http://Dispatchers.IO|Dispatchers.IO>) {
            throw IllegalArgumentException()
        }
    }

    // works fine
    fun loadData() = scope.launch {
        try {
            doWork().await()
        } catch (e: Exception) {
            // exception is caught here
        }
    }

This doesn’t.

// crash FATAL EXCEPTION: DefaultDispatcher-worker-3 @coroutine#1
fun loadData() = scope.launch {
    try {
        val deferred = coroutineScope {
            scope.async(<http://Dispatchers.IO|Dispatchers.IO>) {
                throw IllegalArgumentException()
            }
        }
        deferred.await()
    } catch (e: Exception) {
        // exception is NOT caught here
    }
}

but those 2 samples are completely different

Oops sorry, let me update the code.

what is job for your 2nd example?

Code updated. I just extracted

coroutineScope

into separate method.

Tho this work for you example, but in real code this is really bad code that will not work

suspend fun doWork(): Deferred<String> = coroutineScope {
        async(<http://Dispatchers.IO|Dispatchers.IO>) {

First, check docs of coroutineScope, this function returns only when all child coroutines are finished, I belive this is not what you expect, instead pass coroutinecontext from outside

From the coroutineScope documentation:

* 
 * suspend fun loadDataForUI() = coroutineScope {
 *
 *   val data = async { // <- extension on current scope
 *      ... load some UI data ...
 *   }
 *
 *   withContext(UI) {
 *     doSomeWork()
 *     val result = data.await()
 *     display(result)
 *   }
 * }
 *

yes, and it’s fine example, as you can see it uses async just to run some async job inside of this scope,