public static boolean isSyncCallSafe(ProgressListener listener) {
            if (listener instanceof DeliveryMode) {
                DeliveryMode mode = (DeliveryMode) listener;
                return mode.isSyncCallSafe();
            }
            return listener == null;
        }
Provides convenient method to check if a listener is safe to be invoked
synchronously.
aws-java-sdk-core/src/main/java/com/amazonaws/event/DeliveryMode.java