Struct Backoff 

pub struct Backoff {
    pub first: Duration,
    pub longest: Duration,
    pub attempts: u32,
}

How hard to try when a host is not answering yet.

A host restarts, and every panel connected to it tries to come back. Without spreading those attempts out they arrive together and knock the host over again, so the delay grows and carries a random fraction. The growth stops a dead host being hammered; the randomness stops a live one being hit by a crowd.

Fields

first: Duration

Wait before the second attempt. Doubles from there.

longest: Duration

Ceiling for the wait, before jitter.

attempts: u32

How many attempts in total, including the first.

Implementations

impl Backoff

pub fn first_delay() -> Duration

How long to wait before the very first attempt.

RFC 6455 section 7.2.3 asks for a random delay here specifically, and suggests somewhere between zero and five seconds. This uses that range rather than first, because the point is to scatter a crowd of clients that all woke at once, not to pace one client’s retries.

pub fn delay(self, attempt: u32) -> Duration

How long to wait before attempt attempt, counting the first as 0.

Doubling, capped, then up to a quarter added on top. The jitter comes from the clock rather than a random number generator, which keeps a dependency out for a value that only has to differ between processes.

Trait Implementations

impl Clone for Backoff

fn clone(&self) -> Backoff

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for Backoff

impl Debug for Backoff

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

Formats the value using the given formatter.

impl Default for Backoff

fn default() -> Self

A second, doubling, capped at thirty, giving up after ten attempts.

Ten attempts spans roughly four minutes, which covers a host restart without leaving a caller waiting on one that is never coming back.

impl Eq for Backoff

impl PartialEq for Backoff

fn eq(&self, other: &Backoff) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for Backoff