Introduction

Boomerang is a Rust runtime and composition framework for deterministic reactive systems. It is intended for robotics and embedded products whose software must remain understandable and testable as it grows across teams, cores, processes, and electronic control units (ECUs).

Applications are composed from typed reactors connected by actions and ports. Logical time and an analyzed dependency graph give those components a deterministic execution order. The long-term deployment model separates the application graph from its placement, allowing the same graph to run as one local system, as several local enclaves, or as a federation distributed across multiple targets.

This separation supports an iterative workflow:

1. Develop and test reusable reactors independently.
2. Compose and validate the complete logical graph.
3. Run it locally with accelerated logical time in CI.
4. Apply the production partitioning and exercise it in memory on one host.
5. Deploy the same graph across the target cores and ECUs.
6. Record physical or deployment boundaries and replay selected subsystems for regression and integration testing.

Assembly and Runtime Vocabulary

Boomerang separates declaring the logical application from executing it. Reactor macros and manual APIs use a ReactorContext and ReactionDeclaration to record typed specifications in an Assembly. Lowering resolves assembly keys and deferred factories, producing a RuntimeAssembly whose enclaves can be executed by the runtime or a federation runner:

flowchart LR
    Declare["Declare<br/>contexts and declarations"]
    Assemble["Assemble<br/>logical specifications"]
    Lower["Lower<br/>resolve runtime objects"]
    Execute["Execute<br/>runtime assembly"]

    Declare --> Assemble --> Lower --> Execute

See the Glossary for definitions of these suffixes and the related keys, placement, partition, and runtime concepts.

Boomerang is an early-stage project. Deterministic logical-time execution, local enclaves, modal reactors, recording/replay foundations, and experimental static federation exist today. Deployment-independent partitioning, boundary-layer replay, production multi-ECU deployment, mixed-criticality policies, and no_std support are project goals rather than current guarantees. See Project Goals and Status for the detailed distinction.

Origins

Boomerang is a Rust-first implementation of the Reactors deterministic actor model described by M. Lohstroh, A. Lee, and others at UC Berkeley in Reactors: A Deterministic Model for Composable Reactive Systems.

Lingua Franca is an important point of reference. Boomerang began as a Rust port of its discrete-event scheduler, but uses Rust types and macros for reactor behavior and composition instead of a separate coordination language. See also Reactor C++.