Struct ConnectionLimiter 

pub struct ConnectionLimiter { /* private fields */ }

Track active connections per hostname to enforce max-connection-per-server limit.

Uses DashMap + AtomicUsize for interior mutability, so every method takes &self and the limiter can be shared via Arc<ConnectionLimiter> without any wrapping Mutex/RwLock. This is a soft limiter: the CAS-with-rollback pattern in ConnectionLimiter::try_acquire keeps the global and per-host counts bounded by their limits at the moment of each successful CAS, but snapshot readers (e.g. ConnectionLimiter::host_count) may observe briefly-stale values.

Implementations

impl ConnectionLimiter

pub fn new(global: usize, per_host: usize) -> Self

Create a new ConnectionLimiter with the given global and per-host limits.

pub fn try_acquire(&self, host: &str) -> bool

Try to acquire a connection slot for the given host.

Returns true if the slot was acquired, false if either the global or the per-host limit has been reached.

Algorithm (CAS-with-rollback)

1. Atomically increment global_count via CAS; abort if at/above limit.
2. Atomically increment the per-host counter via CAS; if the per-host limit is hit, roll back the global increment so global_count stays accurate.

This guarantees global_count never exceeds global_limit at the moment of a successful CAS, and each host’s counter never exceeds per_host_limit. A brief shard-level write lock is held by the DashMap Entry guard during the per-host CAS — acceptable for a connection limiter which is not a hot path.

pub fn release(&self, host: &str)

Release a previously-acquired connection slot for the given host.

The caller must call this exactly once per successful try_acquire for the same host. Double-releases are detected via debug_assert! in debug builds.

pub fn host_count(&self, host: &str) -> usize

Current connection count for a host (snapshot — may be slightly stale).

pub fn global_count(&self) -> usize

Total connection count across all hosts (snapshot — may be slightly stale).

pub fn global_limit(&self) -> usize

The configured global connection limit.

pub fn per_host_limit(&self) -> usize

The configured per-host connection limit.

pub fn available_for(&self, host: &str) -> usize

How many slots are still available for the given host (snapshot).

Returns 0 if the host is at or above its per-host limit.