Multi-threading with Rayon crate

This document describes how to use Rayon for parallel processing in TFHE-rs, detailing configurations for single and multi-client applications with code examples.

Single-client application

The problem

The high-level API requires to call set_server_key on each thread where computations need to be done. So a first attempt to use Rayon with TFHE-rs might look like this:

However, due to Rayon's work-stealing mechanism and TFHE-rs' internals, this may create BorrowMutError.

Working example

The correct way is to call rayon::broadcast as follows:

Multi-client applications

For applications that need to operate concurrently on data from different clients and require each client to use multiple threads, you need to create separate Rayon thread pools:

This can be useful if you have some rust #[test], see the example below: