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

fn gen() -> Seed

Generate a new seed

Trait Implementations

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 Copy for Seed

impl Debug for Seed

fn fmt(&self, __arg_0: &mut Formatter) -> Result

Formats the value using the given formatter.