Simulation lifecycle

This lifecycle applies to the legacy simulator. Its Topology::new builds a Nexosim bench, and Topology::run drives the resulting Simulation.

Construction and execution

SimInit::with_num_threads selects Nexosim's single-threaded executor for one worker and its multithreaded executor otherwise. Legacy topology construction then:

1. creates model values and bounded mailboxes
2. registers the models and connects their ports
3. calls SimInit::init to create a Simulation
4. injects the initial source events
5. advances through the configured stop time with step_until

The Days assembly is in legacy/src/topos/topo.rs; the runtime is in crates/nexosim/src/simulation.rs and crates/nexosim/src/simulation/sim_init.rs.

Key APIs

• process_event(&EventId, value) immediately processes a registered event source without advancing simulation time.
• process_event_fn(handler, value, address) is the Days compatibility helper that targets a model input function and address directly.
• process_query(&QueryId, value) immediately processes a registered query and waits for its reply without advancing time.
• step() advances to the next scheduled event or ticker time and processes the work at that time.
• step_until(deadline) repeats that process through the deadline and leaves the clock at the requested time.
• run() processes the queue until it is empty in tickless mode. With a ticker configured, it waits until the scheduler is halted.

Concurrency and ordering

Nexosim can execute ready model tasks concurrently at the same simulated timestamp. Wall-clock task order is therefore not a protocol guarantee. Legacy verification compares canonicalized traces where ordering is semantically irrelevant.

This is separate from exact execution. The exact scalar, CPU, Metal, and CUDA paths use their own canonical EventKey ordering and safe-horizon exchange protocol; see /docs/internals.