Struct ThreadRng 

pub struct ThreadRng { /* private fields */ }

A reference to the thread-local generator

This type is a reference to a lazily-initialized thread-local generator. An instance can be obtained via [rand::rng()][crate::rng()] or via ThreadRng::default(). The handle cannot be passed between threads (is not Send or Sync).

Security

Security must be considered relative to a threat model and validation requirements. The Rand project can provide no guarantee of fitness for purpose. The design criteria for ThreadRng are as follows:

• Automatic seeding via [SysRng] and after every 64 kB of output. Limitation: there is no automatic reseeding on process fork (see below).
• A rigorusly analyzed, unpredictable (cryptographic) pseudo-random generator (see the book on security). The currently selected algorithm is ChaCha (12-rounds). See also StdRng documentation.
• Not to leak internal state through Debug or serialization implementations.
• No further protections exist to in-memory state. In particular, the implementation is not required to zero memory on exit (of the process or thread). (This may change in the future.)
• Be fast enough for general-purpose usage. Note in particular that ThreadRng is designed to be a “fast, reasonably secure generator” (where “reasonably secure” implies the above criteria).

We leave it to the user to determine whether this generator meets their security requirements. For an alternative, see [SysRng].

Fork

ThreadRng is not automatically reseeded on fork. It is recommended to explicitly call ThreadRng::reseed immediately after a fork, for example:

fn do_fork() {
    let pid = unsafe { libc::fork() };
    if pid == 0 {
        // Reseed ThreadRng in child processes:
        rand::rng().reseed();
    }
}

Methods on ThreadRng are not reentrant-safe and thus should not be called from an interrupt (e.g. a fork handler) unless it can be guaranteed that no other method on the same ThreadRng is currently executing.

Implementations

impl ThreadRng

pub fn reseed(&mut self) -> Result<(), Error>

Immediately reseed the generator

This discards any remaining random data in the cache.

Trait Implementations

impl Clone for ThreadRng

fn clone(&self) -> ThreadRng

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for ThreadRng

Debug implementation does not leak internal state

fn fmt(&self, fmt: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl Default for ThreadRng

fn default() -> ThreadRng

Returns the “default value” for a type.

impl TryRng for ThreadRng

type Error = Infallible

The type returned in the event of a RNG error.

fn try_next_u32(&mut self) -> Result<u32, Infallible>

Return the next random u32.

fn try_next_u64(&mut self) -> Result<u64, Infallible>

Return the next random u64.

fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Infallible>

Fill dst entirely with random data.

impl TryCryptoRng for ThreadRng