Dynamic Pipelines in Filament

[rachitnigam]

(Moved from #10)

I was wondering a couple of related questions:

1. Where do non-offset intervals come from and what do they really mean? Ex: [G, L] or [G, max(G, L)+1] as opposed to [G, G+n].
2. What can components that non-trivially use multiple events actually do?

A trivial multi-event component is one that essentially has different "paths"
running through its signals associated with an individual event:

component two_paths<G, L>(
  @[G, G+1] in0: 32,
  @[L, L+1] in1: 32,
) -> (
  @[G+3, G+4] out0: 32,
  @[L+2, L+3] out1: 32,
)

The signature of this components tells us that the two events, G and L do not interact in any observable way; if they did, at least one of the outputs would have a lifetime that depended on both of them.

One of the simplest non-trivial multi-event component is a Latch:

component Latch<G, L>(
  @interface<G, L> write_en: 1,
  @[G, G+1] in: 32
) -> (
  @[G+1, L] out: 32
)

The out signal of the latch requires that it be available till the event L occurs. The write_en signal enforces that the latch cannot be used again till at least the event L has been observed. Because the implementation of the Latch does not provide a way to observe the L event, there is no Filament program that can construct signal available from [G+1, L]; this means Latch is necessarily implemented as an extern.

Another non-trivial multi-event component is the following Join component which provides its output when both the input tokens, left and right arrive:

// A component that triggers when both left and right tokens are available.
component Join<G, L>(
  @interface<G, max(G, L)> left: 1,
  @interface<L, max(G, L)> right: 1,
) -> (
  @[max(G, L), max(G, L) + 1] out: 1,
) {
  LL := new Latch;
  LR := new Latch;
  A := new CombAnd;

  l := LL<G, max(G, L)+1>(left);
  r := LR<L, max(G, L)+1>(right);
  and := A<max(G, L)>(l.out, r.out);

  out = and.out;
}

This is a truly dynamic component: G and L are entirely unrelated and unordered which means either event can fire first. In fact, different invocations can have different orders of G and L firing.
The interface ports for the two events require that the module may not be used till max(G, L) has been observed, which again, is a truly dynamic event in the system.

[rachitnigam]

#1 is also relevant