Function hash_many_multithreaded_with 

pub fn hash_many_multithreaded_with(
    mode: Mode<'_>,
    input: &[u8],
    message_len: usize,
    out: &mut [[u8; 32]],
)

hash_many_multithreaded in any Mode, at its speed.

use blake3_servil::Mode;
let key = [7u8; 32];
let nodes = vec![1u8; 20000 * 64];
let mut macs = vec![[0u8; 32]; 20000];
blake3_servil::hash_many_multithreaded_with(Mode::Keyed(&key), &nodes, 64, &mut macs);
assert_eq!(macs[5], *blake3_servil::hash_with(blake3_servil::Mode::Keyed(&key), &[1u8; 64]).as_bytes());