Struct AdaptiveGate 

pub struct AdaptiveGate { /* private fields */ }

A resizable concurrency permit pool shared by both transfer backends.

The pool starts at start permits and can be retuned live with set_limit anywhere in [1, ceiling]. It serves two access paths over one shared logical limit:

• async (acquire) for the futures/tokio transfer loop, backed by tokio::sync::Semaphore;
• blocking (acquire_blocking) for the rayon store-to-store sync path, backed by a zero-dependency mutex+condvar counting semaphore (mirrors the token-bucket style in crate::transfer).

Both return an RAII guard that releases its permit on drop. set_limit grows the async pool with add_permits and shrinks it by acquiring and forgetting permits (the standard resizable-semaphore technique); for the blocking pool it adjusts the available count and notifies waiters. Shrinking never revokes a permit already held — it only reduces how many new permits can be handed out, so in-flight work drains naturally and shrinking can never deadlock held permits.

The gate is Clone (cloning shares the same underlying pools via Arc).

Implementations

impl AdaptiveGate

pub fn new(start: usize, ceiling: usize) -> Self

Builds a gate whose limit starts at start and can be retuned anywhere in [1, ceiling]. Both start and ceiling are clamped to at least 1, and start is clamped to ceiling.

pub fn ceiling(&self) -> usize

The construction-time ceiling (the maximum the limit can ever reach).

pub fn limit(&self) -> usize

The current logical concurrency limit (shared by both backends).

pub fn set_limit(&self, n: usize) -> usize

Retunes the effective concurrency limit live, clamped to [1, ceiling].

Grows the async pool with add_permits; shrinks it by reserving (and forgetting) the surplus permits so the semaphore’s effective capacity drops without revoking permits already in flight. Adjusts the blocking pool’s available count symmetrically and wakes waiters when growing. Returns the new (clamped) limit.

pub async fn acquire(&self) -> GatePermit

Acquires one async permit, awaiting if the pool is at its current limit. The returned GatePermit releases the permit on drop.

Panics

Never under normal use; the semaphore is only closed when the gate is dropped, which cannot happen while a caller holds an &self.

pub fn acquire_blocking(&self) -> BlockingGatePermit

Blocking sibling of acquire: parks the calling OS thread until a permit is free, then returns a guard that releases it on drop. Used by the rayon store-to-store sync path.

pub fn available_permits(&self) -> usize

Best-effort count of async permits currently available (for tests/metrics).

Trait Implementations

impl Clone for AdaptiveGate

fn clone(&self) -> AdaptiveGate

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for AdaptiveGate

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

Formats the value using the given formatter.