Struct ArticleAvailability 

pub struct ArticleAvailability { /* private fields */ }

Track which backends are known not to have a specific article.

Uses a usize bitset to track which backends returned authoritative 430.

Example with 2 backends

• Initial state: missing=00 (no backend is known missing)
• After backend 0 returns 430: missing=01 (backend 0 doesn’t have it)
• If both return 430: missing=11 (all backends exhausted)

Usage Pattern

This type serves two critical purposes:

1. Cache persistence - Track availability across requests (long-lived)

   • Store authoritative negative facts in cache entries
   • Avoid querying backends known to be missing
   • Updated only after 430 responses

2. 430 retry loop - Track which backends tried during single request (transient)

   • Create fresh instance for each ARTICLE request
   • Mark backends as missing when they return 430
   • Stop when all backends exhausted or one succeeds

Concurrency

Cache entries store this value directly. Memory-cache updates use atomic per-key merge operations, and hybrid-cache updates use per-key locks before replacing an entry. Request-local retry state owns a separate copy, then records each 430 fact directly to the cache.

Implementations

impl ArticleAvailability

pub const fn new() -> Self

Create empty availability - assume all backends have article until proven otherwise

pub fn record_missing(&mut self, backend_id: BackendId) -> &mut Self

Record that a backend returned 430 (doesn’t have the article).

Once marked missing, the backend should not be retried for this cache entry. Later positive observations do not clear the missing bit.

pub fn is_missing(&self, backend_id: BackendId) -> bool

Check if a backend is known to be missing (returned 430)

pub const fn missing_bits(&self) -> usize

Get the raw missing bitset for debugging

pub fn all_exhausted(&self, backend_count: BackendCount) -> bool

Check if all backends in the pool have been tried and returned 430

Check if all backends have been tried and returned 430

pub const fn has_availability_info(&self) -> bool

Check if we have any authoritative backend-missing information.

Returns true if at least one backend is known missing.

pub fn status(&self, backend_id: BackendId) -> BackendStatus

Query backend availability status

Trait Implementations

impl Clone for ArticleAvailability

fn clone(&self) -> ArticleAvailability

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for ArticleAvailability

impl Debug for ArticleAvailability

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

Formats the value using the given formatter.

impl Default for ArticleAvailability

fn default() -> Self

Returns the “default value” for a type.

impl Eq for ArticleAvailability

impl PartialEq for ArticleAvailability

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

Equality operator ==.

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

Inequality operator !=.

impl StructuralPartialEq for ArticleAvailability