Dataflow variables

Hi guys

I'm curious what is the easiest way to imitate dataflow variables in Swi-Prolog
My current idea is something like this (pseudocode):

wait_for(X) :-
	freeze(X, awake_this_thread),
	suspend_this_thread.

test :-
	do_work_in_separate_thread(Results),
	wait_for(Results),
	write(Results).

I'm also interested if there is a way to make those predicates/functions that 
require some of their inputs to be bound to execute to automatically suspend 
until corresponding variables are bound, e.g.:

test :-
	bind_X_in_separate_thread_after_long_calculation(X),
	Y is X+1,
	write(X).

(here I expect for "Y is X+1" to suspend until X gets bound).
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