Thank you for your suggestion.
bleappevt_serialize function seems to put a task at the end of the queue (of application thread) with equal priority.
I believe this function will be called in Bluetooth thread when an registered event happen. The problem is I have no control over the Bluetooth thread at all.
This is a message and NOT an interrupt.
Messages are all serialized.
Hope this helps.
Yes, it seems impossible on this platform.