Struct Candidates 

pub struct Candidates<'a> { /* private fields */ }

The candidates of one selection: a borrowed view of a cluster’s backend list, restricted to the positions a caller retained.

BackendList retains one position per address: when several eligible ids share an address, only their representative (outranks_at_address) is a candidate, so every policy gives that address the share of one backend.

Position i of the view is backends[indices[i]], so a policy that indexes the view (RoundRobin’s cursor, PowerOfTwo’s two samples, Random’s draw) computes exactly the index it computed over the Vec of cloned candidates this view replaces. Building the view borrows and copies nothing: the caller owns indices, and only the backend a policy returns has its Rc cloned.

The view also carries the instant the selection happens at, which a policy reading LoadMetric::ConnectionTime decays each average to: no policy reads a clock of its own (#1684).

Implementations

impl<'a> Candidates<'a>

pub fn new( backends: &'a [Rc<RefCell<Backend>>], indices: &'a [usize], now: Instant, ) -> Self

View backends through indices for a selection at now. Every index must address a slot of backends, and the indices must be strictly increasing.

pub fn with_siblings( backends: &'a [Rc<RefCell<Backend>>], indices: &'a [usize], siblings: &'a [usize], now: Instant, ) -> Self

Candidates::new with the sibling ring of backends (see the field docs), which Candidates::siblings walks so a load-aware policy can read the load of a whole address.

pub fn siblings( &self, index: usize, ) -> impl Iterator<Item = &'a Rc<RefCell<Backend>>> + use<'a>

Every OTHER backend at the address of the candidate at index, eligible or not: the ids a collapsed address hides behind its representative. Empty without a sibling ring, and for an address with one id, which costs one read.

pub fn now(&self) -> Instant

The instant this selection happens at.

pub fn len(&self) -> usize

pub fn is_empty(&self) -> bool

pub fn get(&self, index: usize) -> Option<&'a Rc<RefCell<Backend>>>

The candidate at position index of the view.

pub fn iter( &self, ) -> impl ExactSizeIterator<Item = &'a Rc<RefCell<Backend>>> + use<'a>

The candidates in view order.

Trait Implementations

impl<'a> Clone for Candidates<'a>

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<'a> Copy for Candidates<'a>

impl<'a> Debug for Candidates<'a>

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

Formats the value using the given formatter.

impl Index<usize> for Candidates<'_>

type Output = Rc<RefCell<Backend>>

The returned type after indexing.

fn index(&self, index: usize) -> &Self::Output

Performs the indexing (container[index]) operation.