Hmm, this code hangs forever for me using 1.3.30:

withTimeoutOrNull(100) {
    suspendCoroutine<Unit> { cont ->
        (context.getSystemService(Context.INPUT_METHOD_SERVICE) as InputMethodManager)
            .hideSoftInputFromWindow(windowToken, 0, object : ResultReceiver(handler) {
                override fun onReceiveResult(resultCode: Int, resultData: Bundle?) {
                    cont.resume(Unit)
                }
            })
    }
}

Yes, that's expected as cancellation is cooperative. Use

suspenCancellableCoroutine

and unregister the receiver in a finally block, or in cont.invokeOnClose.

That’s not the issue. First of all you cannot unregister the receiver and secondly it shouldn’t matter as withTimeout should still continue and just let the other coroutine be, ignoring it when it (if ever) resumes

Because cancellation is part of kotlinx.coroutines, and because in some cases, your code is not cancellable (e.g. blocking code).

I thought the only difference was that you could perform more efficient cleanup using the latter

Try finally works for both, but for the non cancellable, it happens only if your code throws or is done as it will not receive the cancellation signal.