Struct Permit 

pub struct Permit { /* private fields */ }

RAII permit that holds a semaphore slot for the lifetime of a handler task.

On the success path of ConnectionLimiter::acquire (acquire_inner), the limiter calls Metrics::dispatch_permit_acquired() immediately before constructing this struct; Drop calls Metrics::dispatch_permit_released() unconditionally. The two calls must remain paired: every successful construction is matched by exactly one drop, and the gauge stays balanced.

_sem is Option so the max_concurrent_handlers = 0 disabled-cap mode can return a Permit without holding a semaphore slot — the in-flight gauge still tracks the handler, and Drop releases nothing (the OwnedSemaphorePermit is None).

#[must_use]: dropping the permit immediately (let _ = limiter.acquire(&conn);) would defeat the purpose of acquiring it — the slot is freed before the handler runs, so the cap fails to bound concurrency.

Trait Implementations

impl Debug for Permit

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

Formats the value using the given formatter.

impl Drop for Permit

fn drop(&mut self)

Executes the destructor for this type.

fn pin_drop(self: Pin<&mut Self>)

🔬This is a nightly-only experimental API. (pin_ergonomics)

Execute the destructor for this type, but different to Drop::drop, it requires self to be pinned.