What is the best way to simulate thousands of state machines that communicate with each other?

To introduce my context, I have a project that aims to simulate multiple state machines that communicate with each other. Currently, the project is based on a queue of activities that are consumed and produced by a single thread.

Part of the goal of the project is to measure how much of the simulation time it takes for any two state machines to communicate with each other, taking into account several factors associated with the simulation process.

There are Java libraries that handle the simulation process very well, such as Spring, but I haven’t found many resources on the process of creating multiple state machines, let alone communicating between them efficiently.

What would be a suitable library for simulating multiple state machines? What would be a suitable and efficient way of communicating between them?

The computers on which this project is usually run are not very powerful. And the simulations often take hours.

I would like to reduce the time and hardware requirements when evaluating more suitable approaches. Thank you for your time.