What is the best way to check by CancellationExcep...

# coroutines

[PHondogo]

What is the best way to check by CancellationException that coroutine was cancelled without Exception?
Now I'm using such logic (in thread):

[PHondogo]

// if cause is null then it is non exceptional cancellation
fun getCancellationExceptionCause(e: CancellationException): Throwable? {
    val causes = HashSet<Throwable>()
    var cause = e.cause
    while (cause != null) {
        if (cause !is CancellationException) {
            return cause
        }
        if (!causes.add(cause)) {
            break
        }
        cause = cause.cause
    }
    return null
}

[Sam]

Can you say more about what you mean? If the coroutine failed, I'd expect you would see a different exception, not a CancellationException.

[PHondogo]

Please consider this code:

try {
    coroutineScope {
        //cancel() // normal cancel
        cancel(cause = CancellationException(Exception("test"))) // exceptional case
    }
} catch (e: CancellationException) {
    val cause = getCancellationExceptionCause(e) // fun from previous message
    if (cause != null) {
        throw cause
    }
}

[PHondogo]

In case of not catching like this normal cancellation propagated out of coroutineScope

[Sam]

I'm not sure I agree with the distinction between "exceptional" and "normal" in your example. A cancellation is always a normal termination. The 'cause' is just there for informational or debugging purposes. If you have a failure, you should just throw Exception("test") instead of calling cancel().
As an aside, calling cancel() inside a coroutineScope to cancel the current coroutine introduces a new problem of its own, so there's more going on here than a simple cancellation. That's because coroutineScope returns a result. Attempting to retrieve a result from a cancelled coroutine will raise a new cancellation exception, which is not normally a good thing 😞.