Re: Dataflow variables

On 11/03/2013 04:50 PM, Aleksey wrote:
> 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.

One problem here is that threads share terms nor variables. The only
ways to talk to each other is by using shared dynamic predicates or
message queues.  Some systems (e.g., Ciao) have the ability to suspend
on clauses being added to a dynamic predicate.  That is easy enough to
implement.  I guess this would mean we have to revert to the immediate
update model for such predicates though.  Never studied this facility
in enough detail.

Sharing variables (and terms) between threads would be interesting, but
requires a quite different design.

	Cheers --- Jan


>
> 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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