> For the complete documentation index, see [llms.txt](https://docs.zama.org/tfhe-rs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.zama.org/tfhe-rs/fhe-computation/advanced-features/rayon-crate.md). # 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. [Rayon](https://crates.io/crates/rayon) is a popular Rust crate that simplifies writing multi-threaded code. You can use Rayon to write multi-threaded **TFHE-rs** code. However, due to the specifications of Rayon and **TFHE-rs**, certain setups are necessary. ## 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: ```rust use tfhe::prelude::*; use tfhe::{ConfigBuilder, set_server_key, FheUint8, generate_keys}; fn main() { let (cks, sks) = generate_keys(ConfigBuilder::default()); let xs = [ FheUint8::encrypt(1u8, &cks), FheUint8::encrypt(2u8, &cks), ]; let ys = [ FheUint8::encrypt(3u8, &cks), FheUint8::encrypt(4u8, &cks), ]; // set_server_key in each closure as they might be // running in different threads let (a, b) = rayon::join( || { set_server_key(sks.clone()); &xs[0] + &ys[0] }, || { set_server_key(sks.clone()); &xs[1] + &ys[1] } ); } ``` 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: ```rust use tfhe::prelude::*; use tfhe::{ConfigBuilder, set_server_key, FheUint8, generate_keys}; fn main() { let (cks, sks) = generate_keys(ConfigBuilder::default()); // set the server key in all of the rayon's threads so that // we won't need to do it later rayon::broadcast(|_| set_server_key(sks.clone())); // Set the server key in the main thread set_server_key(sks); let xs = [ FheUint8::encrypt(1u8, &cks), FheUint8::encrypt(2u8, &cks), ]; let ys = [ FheUint8::encrypt(3u8, &cks), FheUint8::encrypt(4u8, &cks), ]; let (a, b) = rayon::join( || { &xs[0] + &ys[0] }, || { &xs[1] + &ys[1] } ); let a: u8 = a.decrypt(&cks); let b: u8 = b.decrypt(&cks); assert_eq!(a, 4u8); assert_eq!(b, 6u8); } ``` ## 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: ```rust use tfhe::prelude::*; use tfhe::{ConfigBuilder, set_server_key, FheUint8, generate_keys}; fn main() { let (cks1, sks1) = generate_keys(ConfigBuilder::default()); let xs1 = [ FheUint8::encrypt(1u8, &cks1), FheUint8::encrypt(2u8, &cks1), ]; let ys1 = [ FheUint8::encrypt(3u8, &cks1), FheUint8::encrypt(4u8, &cks1), ]; let (cks2, sks2) = generate_keys(ConfigBuilder::default()); let xs2 = [ FheUint8::encrypt(100u8, &cks2), FheUint8::encrypt(200u8, &cks2), ]; let ys2 = [ FheUint8::encrypt(103u8, &cks2), FheUint8::encrypt(204u8, &cks2), ]; let client_1_pool = rayon::ThreadPoolBuilder::new().num_threads(4).build().unwrap(); let client_2_pool = rayon::ThreadPoolBuilder::new().num_threads(2).build().unwrap(); client_1_pool.broadcast(|_| set_server_key(sks1.clone())); client_2_pool.broadcast(|_| set_server_key(sks2.clone())); let ((a1, b1), (a2, b2)) = rayon::join(|| { client_1_pool.install(|| { rayon::join( || { &xs1[0] + &ys1[0] }, || { &xs1[1] + &ys1[1] } ) }) }, || { client_2_pool.install(|| { rayon::join( || { &xs2[0] + &ys2[0] }, || { &xs2[1] + &ys2[1] } ) }) }); let a1: u8 = a1.decrypt(&cks1); let b1: u8 = b1.decrypt(&cks1); assert_eq!(a1, 4u8); assert_eq!(b1, 6u8); let a2: u8 = a2.decrypt(&cks2); let b2: u8 = b2.decrypt(&cks2); assert_eq!(a2, 203u8); assert_eq!(b2, 148u8); } ``` This can be useful if you have some rust `#[test]`, see the example below: ```rust // Pseudo code #[test] fn test_1() { let pool = rayon::ThreadPoolBuilder::new().num_threads(4).build().unwrap(); pool.broadcast(|_| set_server_key(sks1.clone())); pool.install(|| { let result = call_to_a_multithreaded_function(...); assert_eq!(result, expected_value); }) } #[test] fn test_2() { let pool = rayon::ThreadPoolBuilder::new().num_threads(4).build().unwrap(); pool.broadcast(|_| set_server_key(sks1.clone())); pool.install(|| { let result = call_to_another_multithreaded_function(...); assert_eq!(result, expected_value); }) } ``` --- # Agent Instructions This documentation is published with GitBook. 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