Asynchronix

A high-performance asynchronous computation framework for system simulation.

What is this?

Warning: this page is at the moment mostly addressed at interested contributors, but resources for users will be added soon.

In a nutshell, Asynchronix is an effort to develop a framework for discrete-event system simulation, with a particular focus on cyberphysical systems. In this context, a system might be something as large as a spacecraft, or as small as a IoT device.

Asynchronix draws from experience in the space industry but differs from existing tools in a number of respects, including:

1. open-source license: it is distributed under the very permissive MIT and Apache 2 licenses, with the intent to foster an ecosystem where models can be easily exchanged without reliance on proprietary APIs,
2. developer-friendly technology: Rust's support for algebraic types and its powerful type system make it ideal for the "cyber" part in cyberphysical, i.e. for modelling digital devices with state machines,
3. very fast: by leveraging Rust's excellent support for multithreading and async programming, simulation models can run efficiently in parallel with all required synchronization being transparently handled by the simulator.

General design

Asynchronix is an async compute framework for time-based discrete event simulation.

From the perspective of simulation model implementers and users, it closely resembles a flow-based programming framework: a model is essentially an isolated entity with a fixed set of typed inputs and outputs, communicating with other models and with the scheduler through message passing. Unlike in conventional flow-based programming, however, request-response patterns are also possible.

Under the hood, Asynchronix' implementation is based on async Rust and the actor model. All inputs are forwarded to a single "mailbox" (an async channel), preserving the relative order of arrival of input messages.

Computations proceed at discrete times. When executed, models can post events for the future, i.e. request the delayed activation of an input. Whenever the computation at a given time completes, the scheduler selects the nearest future time at which one or several events are scheduled, thus triggering another set of computations.

This computational process makes it difficult to use general-purposes runtimes such as Tokio, because the end of a set of computations is technically a deadlock: the computation completes when all model have nothing left to do and are blocked on an empty mailbox. Also, instead of managing a conventional reactor, the runtime manages a priority queue containing the posted events. For these reasons, it was necessary for Asynchronix to develop a fully custom runtime.

Another crucial aspect of async compute is message-passing efficiency: oftentimes the processing of an input is a simple action, making inter-thread message-passing the bottleneck. This in turns calls for a very efficient channel implementation, heavily optimized for the case of starved receivers since models are most of the time waiting for an input to become available.

Current state

The simulator is rapidly approaching MVP completion and has achieved 2 major milestones:

• completion of an extremely fast asynchronous multi-threaded channel, demonstrated in the Tachyonix project; this channel is the backbone of the actor model,
• completion of a custom async executor optimized for message-passing and deadlock detection, which has demonstrated even better performance than Tokio for message-passing; this executor is already in the main branch and can be tested against other executors using the Tachyonix benchmark.

Before it becomes usable, however, further work is required to implement the priority queue, implement model inputs and outputs and adapt the channel.

License

This software is licensed under the Apache License, Version 2.0 or the MIT license, at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.