Struct tokio::sync::batch_semaphore::Semaphore

pub(crate) struct Semaphore {
    waiters: Mutex<Waitlist>,
    permits: AtomicUsize,
}

An asynchronous counting semaphore which permits waiting on multiple permits at once.

Fields

waiters: Mutex<Waitlist>

permits: AtomicUsize

The current number of available permits in the semaphore.

Implementations

impl Semaphore

pub(crate) const MAX_PERMITS: usize = 2_305_843_009_213_693_951usize

The maximum number of permits which a semaphore can hold.

Note that this reserves three bits of flags in the permit counter, but we only actually use one of them. However, the previous semaphore implementation used three bits, so we will continue to reserve them to avoid a breaking change if additional flags need to be added in the future.

const CLOSED: usize = 1usize

const PERMIT_SHIFT: usize = 1usize

pub(crate) fn new(permits: usize) -> Self

Creates a new semaphore with the initial number of permits

Maximum number of permits on 32-bit platforms is 1<<29.

pub(crate) const fn const_new(permits: usize) -> Self

Creates a new semaphore with the initial number of permits.

Maximum number of permits on 32-bit platforms is 1<<29.

pub(crate) fn new_closed() -> Self

Creates a new closed semaphore with 0 permits.

pub(crate) const fn const_new_closed() -> Self

Creates a new closed semaphore with 0 permits.

pub(crate) fn available_permits(&self) -> usize

Returns the current number of available permits.

pub(crate) fn release(&self, added: usize)

Adds added new permits to the semaphore.

The maximum number of permits is usize::MAX >> 3, and this function will panic if the limit is exceeded.

pub(crate) fn close(&self)

Closes the semaphore. This prevents the semaphore from issuing new permits and notifies all pending waiters.

pub(crate) fn is_closed(&self) -> bool

Returns true if the semaphore is closed.

pub(crate) fn try_acquire( &self, num_permits: usize ) -> Result<(), TryAcquireError>

pub(crate) fn acquire(&self, num_permits: usize) -> Acquire<'_>

fn add_permits_locked(&self, rem: usize, waiters: MutexGuard<'_, Waitlist>)

Release rem permits to the semaphore’s wait list, starting from the end of the queue.

If rem exceeds the number of permits needed by the wait list, the remainder are assigned back to the semaphore.

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

Decrease a semaphore’s permits by a maximum of n.

If there are insufficient permits and it’s not possible to reduce by n, return the number of permits that were actually reduced.

fn poll_acquire( &self, cx: &mut Context<'_>, num_permits: usize, node: Pin<&mut Waiter>, queued: bool ) -> Poll<Result<(), AcquireError>>

Trait Implementations

impl Debug for Semaphore

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

Formats the value using the given formatter.