Struct WeightedFairQueue 

pub struct WeightedFairQueue<T> { /* private fields */ }

Weighted-fair queue, parameterized over item type T.

Maintains one virtual sub-queue per active database_id. The dispatcher calls pop_next() to retrieve the next item following deficit round-robin ordering. Total capacity across all virtual queues is bounded; try_enqueue returns Err(item) when the total is full.

Implementations

impl<T> WeightedFairQueue<T>

pub fn new(capacity: usize, reap_after_pops: usize) -> Self

Create a new weighted-fair queue with the given total capacity and reap threshold. reap_after_pops controls how many empty queues persist after draining before being garbage-collected.

pub fn try_enqueue(&mut self, database_id: u64, item: T) -> Result<(), T>

Attempt to enqueue item for database_id. Returns Err(item) if the total queue has reached capacity.

pub fn set_priority(&mut self, database_id: u64, cls: PriorityClass)

Set (or update) the priority class for a database. Applied on the next pop_next call after this update.

pub fn pop_next(&mut self) -> Option<T>

Pop the next item using deficit round-robin across all virtual queues.

Returns None if all virtual queues are empty.

Each database is served for up to priority_weight(class) consecutive items before the scheduler rotates to the next database. Deficit credits are added once per turn (when a DB’s deficit reaches zero and it re-enters the front of the rotation) and carried across calls so databases with lower arrival rates still accumulate credits fairly.

pub fn depth_for(&self, database_id: u64) -> usize

Number of items queued for a specific database.

pub fn total_depth(&self) -> usize

Total items across all virtual queues.

pub fn is_throttled_for(&self, database_id: u64) -> bool

Returns true if the given database’s virtual queue has reached ≥ 85% of its fair share of total capacity.

Fair share = capacity / active_databases (floor division, min 1). Databases with higher priority class receive proportionally more fair share in the weight sense but the slot fair share is still equal (per-DB slot pressure uses equal division to avoid one class starving another’s absolute headroom).

pub fn is_suspended_for(&self, database_id: u64) -> bool

Returns true if the given database’s virtual queue has reached ≥ 95% of its fair share of total capacity.

pub fn active_database_count(&self) -> usize

Number of active virtual queues (including empty, not-yet-reaped ones).