Why does the below logic crashes where as if i separate the top-level it doesn't. val toplevel = Cor...

# coroutines

[Vikas Singh]

Why does the below logic crashes where as if i separate the top-level it doesn't.
val toplevel = CoroutineScope(Dispatchers.IO)
this crashes:
toplevel.launch {
val sync = async {
print("this is sync 1")
throw RuntimeException()
}
try {
sync.await()
} catch (e: Exception) {
print("Exception handled")
}
}

This does not:
val sync = toplevel.async {
print("this is sync 1")
throw RuntimeException()
}
toplevel.launch
try {
sync.await()
} catch (e: Exception) {
print("Exception handled")
}
}

[Sam]

Because when async fails it also causes its parent job to fail

[Sam]

In your first example, the parent of async is the launch job, so when the async job fails, the launch job fails too. It might never reach the catch because the job could fail before it got there.

[Sam]

In the second example, the async job has no parent job so the failure doesn’t propagate anywhere until you call await().

[Vikas Singh]

If i surround async with try catch it should be able to handle it right ? for the first case where parent is launch

[Sam]

No, because the error isn’t thrown when you call async. The call to async just starts the job and then returns immediately. The error happens later, in the background, and propagates directly to the parent job.