Struct fasthash::Seed

pub struct Seed(_);

Generate hash seeds

It base on the same workflow from std::collections::RandomState

Historically this function did not cache keys from the OS and instead simply always called rand::thread_rng().gen() twice. In #31356 it was discovered, however, that because we re-seed the thread-local RNG from the OS periodically that this can cause excessive slowdown when many hash maps are created on a thread. To solve this performance trap we cache the first set of randomly generated keys per-thread.

Later in #36481 it was discovered that exposing a deterministic iteration order allows a form of DOS attack. To counter that we increment one of the seeds on every RandomState creation, giving every corresponding HashMap a different iteration order.

Examples

use fasthash::{Seed, city};

city::hash128_with_seed(b"hello world", Seed::gen().into());

Methods

impl Seed

pub fn gen() -> Seed

Generate a new seed

Trait Implementations

impl Copy for Seed

impl From<Seed> for u32

fn from(seed: Seed) -> u32

Performs the conversion.

impl From<Seed> for u64

fn from(seed: Seed) -> u64

Performs the conversion.

impl From<Seed> for (u64, u64)

fn from(seed: Seed) -> (u64, u64)

Performs the conversion.

impl From<Seed> for (u64, u64, u64, u64)

fn from(seed: Seed) -> (u64, u64, u64, u64)

Performs the conversion.

impl From<Seed> for u128

fn from(seed: Seed) -> u128

Performs the conversion.

impl Clone for Seed

fn clone(&self) -> Seed

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Seed

fn fmt(&self, f: &mut Formatter) -> Result

Formats the value using the given formatter.