Trait Meter

Source

pub trait Meter:
    Send
    + Sync
    + Debug {
    // Required methods
    fn try_debit(&self, cost: u64) -> Option<u64>;
    fn credit(&self, cost: u64, epoch: u64);
    fn time_until(&self, cost: u64) -> Duration;
    fn snapshot(&self) -> MeterStatus;
}

Expand description

A throttle that admits or rejects weighted units, exposing enough state to compose several into a MultiRateLimiter and to answer “which limit blocked me, and for how long”.

Implemented by both RateLimiter (continuous token bucket) and WindowedRateLimiter (fixed-window counter), so a single gate can mix the two. The trait is deliberately synchronous — the async acquire paths are built on try_debit + time_until + tokio::time::sleep, which keeps Meter object-safe and lets a composite never double-debit. Units are weighted (cost): a request-count tier uses cost = 1; a usage-metered tier uses the call’s cost (e.g. token count).

Required Methods§

Source

fn try_debit(&self, cost: u64) -> Option<u64>

Debit cost units if capacity allows. Returns Some(epoch) on success — an opaque token identifying the accounting session the debit belongs to, which must be passed back to credit to refund it — or None if rejected. No metrics.

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fn credit(&self, cost: u64, epoch: u64)

Return cost units previously debited in epoch (used by Reservation rollback). If the meter’s accounting has moved on (e.g. a fixed window has since reset), the refund no longer applies and is silently dropped. No metrics.

Source