Struct ExponentialBackoff 

pub struct ExponentialBackoff<const SPIN_LIMIT: usize, const UNTIL_UNCHANGED_LIMIT: usize = 0, const YIELD_AFTER: usize = { usize::MAX }> { /* private fields */ }

Performs exponential backoff.

Each backoff iteration iter (starting from 0) calls spin_loop 1 << iter.min(SPIN_LIMIT) times.

During the first UNTIL_UNCHANGED_LIMIT backoff iterations, backoff continues until the atomic’s value stops changing between reloads; after that, the CAS is retried after a single reload to avoid starvation.

After YIELD_AFTER backoff iterations (and if the std feature is enabled), yield_now is called instead of spinning.

For reference, crossbeam::utils::Backoff is equivalent to ExponentialBackoff<6> with Backoff::spin, and ExponentialBackoff<10, 0, 7> with Backoff::snooze. However, UNTIL_UNCHANGED_LIMIT should also be used in contended CAS loop to further reduce contention.

Implementations

impl<const SPIN_LIMIT: usize, const UNTIL_UNCHANGED_LIMIT: usize, const YIELD_AFTER: usize> ExponentialBackoff<SPIN_LIMIT, UNTIL_UNCHANGED_LIMIT, YIELD_AFTER>

pub fn starts_at(iter: usize) -> Self

Starts an exponential backoff at the given iteration (starting from 0).

This constructor can be used to skip the first smaller iterations.

pub fn iter_count(&self) -> usize

Returns the current count of backoff iterations performed.

It can be used for example to switch to another algorithm, like thread parking, after a given iteration count.

Trait Implementations

impl<const SPIN_LIMIT: usize, const UNTIL_UNCHANGED_LIMIT: usize, const YIELD_AFTER: usize> BackoffStrategy for ExponentialBackoff<SPIN_LIMIT, UNTIL_UNCHANGED_LIMIT, YIELD_AFTER>

fn backoff(&mut self) -> RetryStrategy

Performs backoff and returns how the CAS should be retried.

fn will_reload(&self) -> bool

Returns true if the next call to backoff will not return RetryStrategy::NoReload.

const BACKOFF: bool = true

Whether the strategy does backoff or not.

fn backoff_reload<T: PartialEq, F: FnMut() -> T>( &mut self, current: T, reload: F, ) -> T

Performs backoff after a failed CAS and reloads the atomic value according to the returned RetryStrategy.

fn backoff_until<C: BackoffUntilCondition, F: FnMut() -> C>( &mut self, f: F, ) -> C::Result

Loops until a condition is fulfilled, performing backoff at each iteration.

impl<const SPIN_LIMIT: usize, const UNTIL_UNCHANGED_LIMIT: usize, const YIELD_AFTER: usize> Debug for ExponentialBackoff<SPIN_LIMIT, UNTIL_UNCHANGED_LIMIT, YIELD_AFTER>

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

Formats the value using the given formatter.

impl<const SPIN_LIMIT: usize, const UNTIL_UNCHANGED_LIMIT: usize, const YIELD_AFTER: usize> Default for ExponentialBackoff<SPIN_LIMIT, UNTIL_UNCHANGED_LIMIT, YIELD_AFTER>

fn default() -> ExponentialBackoff<SPIN_LIMIT, UNTIL_UNCHANGED_LIMIT, YIELD_AFTER>

Returns the “default value” for a type.