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() 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 rigorously 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.

Forks and interrupts

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.

Panics

Implementations of TryRng and Rng panic in case of SysRng failure during reseeding (highly unlikely).

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