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Seed Many RNGs in Rust

There are different ways to seed many RNGs (for parallel RNGs). Below summarizes 3 popular ways. Seeding RNGs using std::collections::hash_map::RandomState or rand::thread_rng is preferred.

Seed Using System Time

use std::time::{SystemTime, UNIX_EPOCH};
use rand::SmallRng;

fn main () {
    let seed = SystemTime::now()
        & ((1 << 65) - 1);
    let mut rng = SmallRng::seed_from_u64(seed);

Seed Using std::collections::hash_map::RandomState

std::collections::hash_map::RandomState gets true (or close to true) random bytes using entropy as the base random state which is cached using thread-local storage. Subsequent instantiations increment the random state to ensure different states.

use std::collections::hash_map::RandomState;
use std::hash::{BuildHasher, Hasher};
use rand::SmallRng;

fn main() {
    let seed = RandomState::new().build_hasher().finish();
    let mut rng = Xoshiro256PlusPlus::seed_from_u64(seed);

Seed Using a Master RNG

use rand::{SmallRng, thread_rng};

fn main() {
    let mut rng = SmallRng::from_rng(thread_rng()).unwrap();