Enum SubscriptionSlot 

pub enum SubscriptionSlot<D> {
    Idle,
    Reserved,
    Active(D),
}

The one inner subscription an operator holds at a time.

D is the value being held — a Subscription in every current use, which disposes when dropped.

Variants

Idle

Nothing is subscribed and nothing is being subscribed.

Reserved

A subscription is being built with the lock released. Reserving the slot up front is what tells a concurrent update that a subscription is on its way.

Active(D)

A subscription is held.

Implementations

impl<D> SubscriptionSlot<D>

pub fn is_idle(&self) -> bool

Whether the slot is Idle.

pub fn is_reserved(&self) -> bool

Whether the slot is Reserved.

pub fn reserve(&mut self) -> Option<D>

Reserves the slot for a subscription that is about to be built, and gives back the subscription it replaces, if any, to drop outside the lock.

Panics

Panics if the slot is already reserved: only one build can be in flight, since the caller reserves under the same lock that serializes its updates.

pub fn reserve_if_idle(&mut self) -> bool

Reserves the slot only if it is Idle, so nothing is ever evicted, and returns whether it did.

This is the form used by a host that keeps one task alive while there is work to do: it starts a task only when none is running, instead of replacing a running one.

pub fn fill(&mut self, value: D) -> Option<D>

Fills a reserved slot with the subscription that was built.

Returns Some when the slot was released while the build was running — the operator terminated the inner subscription in the meantime — in which case the value was not stored and is given back to drop outside the lock.

Panics

Panics if the slot is already active, which would mean a build was never reserved.

pub fn release(&mut self) -> Option<D>

Releases the slot, giving back the held subscription, if any, to drop outside the lock.

Releasing a Reserved slot returns None and makes the pending fill give its subscription back instead of storing it.

Trait Implementations

impl<D> Debug for SubscriptionSlot<D>

where D: Debug,

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

Formats the value using the given formatter.