governor 0.1.0

A rate-limiting implementation in Rust

governor - a library for regulating the flow of data

This library is an implementation of the Generic Cell Rate Algorithm for rate limiting in Rust programs.

It is intended to help your program know how much strain it is supposed to put on external services (and, to some extent, to allow your services to regulate how much strain they take on from their users). In a way, it functions like the iconic steam governor from which this library takes its name:

a centrifugal governor

Implementation and constraints

The rate-limiting algorithms in this crate are implemented using the Generic Cell Rate Algorithm (GCRA). The GCRA is functionally equivalent to a leaky bucket, but has a few advantages over most leaky bucket implementations:

  • No background "drip" process is necessary to keep up maintenance on the bucket,
  • it updates its state, whenever a request comes in, continuously on a nanosecond scale, and
  • it keeps its state in a single AtomicU64 integer.

The rate-limiting state used here does not take up much memory (only 64 bits!) and is updated thread-safely with a compare-and-swap operation. Compared to ratelimit_meter's implementation using Mutexes, it is on average 10x faster when used on multiple threads.


The speed comes at a slight cost: Each rate-limiter and its state is only useful for 584 years after creation. If you are trying to power the Long Now Foundation's computers with this library, please get in touch.