Struct TokenBucket 

pub struct TokenBucket { /* private fields */ }

Token bucket rate limiter.

Implements the token bucket algorithm where tokens are added at a fixed rate up to a maximum capacity. Each request consumes one token.

The rate is a fraction of a token per second, not a whole number. A limit of 3 requests a minute is 0.05 tokens a second; when the rate was carried as an integer that rounded to 0, the bucket never refilled, and a client that spent its burst was locked out until the process restarted.

The count and the time it was last brought up to date live under one lock. They used to be two atomics updated by separate compare-and-swaps, which let two concurrent requests both credit the same elapsed time.

Implementations

impl TokenBucket

pub fn new(capacity: u64, refill_rate: f64) -> Self

Create a new token bucket, full.

Arguments

• capacity - Maximum tokens (burst size)
• refill_rate - Tokens added per second; may be fractional

pub fn try_acquire(&self) -> bool

Try to consume a token.

Returns true if a token was available and consumed, false otherwise.

pub fn try_acquire_n(&self, n: u64) -> bool

Try to consume N tokens.

Returns true if N tokens were available and consumed, false otherwise.

pub fn available(&self) -> u64

Get current available tokens (approximate).

pub fn is_full(&self) -> bool

Whether the bucket has refilled completely.

A full bucket is indistinguishable from a fresh one, so the limiter can forget it without changing any future answer.