Ports & mailboxes

Nexosim models communicate via typed message passing:

• Mailbox<T>: the inbound queue for a model
• Output<T>: a typed, connectable output port
• EventSlot<T>: a sink that can be used to observe outputs in the bench harness

Source: days/crates/nexosim/src/ports.rs

Connecting models

During bench assembly, an Output<T> is connected to a handler method on another model:

producer.output.connect(Consumer::handle, &consumer_mailbox);

When the producer sends:

producer.output.send(msg).await;

Nexosim schedules delivery of the message into the consumer’s mailbox at the current (or delayed) simulation time.

How Days uses this

Days builds a graph of models where, for example:

• PacketSwitch.outputs[next_id] connects to either
  • a scheduler’s packet_received, or
  • a sink/source endpoint handler
• schedulers connect their output to downstream switches (optionally through an L2 pipeline)

The important architectural property is that models own their state and only communicate through these ports, which makes it feasible to run many models concurrently.