futures (Re: [net2-wg] Packet interface)

[Gilman Tolle]

> This is the point I think might generate confusion: if each client has
> to allocate entries for each destination, this can be a hard decision
> to make statically.

If I were writing a multiple-destination protocol on top of a layer
like this, I'd have to make two decisions:
* how many send pool entries do I need? (static)
* which entry do I use for a particular send? (dynamic)

Like Rodrigo says, the first is a hard decision to make statically in
the point-to-point case, so let's say that the client just picks
"enough", balancing RAM requirements with communication multiplexing.

I can think of two different ways to make the second decision:
* pick any inactive entry for a new send
* pick an entry that has a particular destination and increase its
futures, for an additional send

Both of these decisions require less coding on the client if, instead
of allocating individual pool entries, the client allocates a pool
with N entries, which is a portion of the overall global pool, and
requests an entry before filling it in and sending it. The entry could
be requested according to free-ness, or by destination.

How else would you use this interface?

Gil