Struct DirectionState 

struct DirectionState {
    acquirer: BandwidthAcquirer,
    max_chunk: NonZero<usize>,
}

Rate-limiting state for a single direction.

It has everything needed to rate limit one direction that is a BandwidthAcquirer and an optional maximum chunk.

This is used by the GlobalRateLimitedReader and GlobalRateLimitedWriter as they share that same behavior for each direction (read and write).

Fields

acquirer: BandwidthAcquirer

Acquirer used to get a Permit from the pool for each poll.

max_chunk: NonZero<usize>

Cap on how many tokens a single IO can request.

An IO requests at most this many tokens as long as the buffer is bigger.

Implementations

impl DirectionState

fn new(acquirer: BandwidthAcquirer, max_chunk: NonZero<usize>) -> Self

Constructor.

fn poll_acquire( &mut self, cx: &mut Context<'_>, tokens: usize, ) -> Poll<Result<Permit, Error>>

Acquire a permit for an IO of the given amount of tokens.

The request is capped to the state’s max chunk. The grant itself is capped to the pool capacity so the returned Permit can hold less than tokens.

The Permit is handed to the caller rather than kept here so that it lives exactly as long as the IO attempt it is for. If the underlying IO turns out to be Poll::Pending, the caller drops it and the tokens are refunded to the pool instead of being parked for as long as the connection is not ready. That matters with many connections as we don’t want to hold off ready connections on already allocated permits for non ready connections.

The cost is that the caller re-acquires on the next poll rather than resuming with what it already had. It is by design.

fn commit(permit: Permit, tokens: usize)

Claim tokens on permit after a successful IO.

tokens must not exceed what the permit was granted. Callers get that by capping the IO to Permit::granted.

The permit is consumed so whatever is left unclaimed is refunded on drop.

Trait Implementations

impl Debug for DirectionState

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

Formats the value using the given formatter.