Struct async_utils::hanging_get::server::HangingGetInner

pub struct HangingGetInner<S, K, O, F: Fn(&S, O) -> bool> { /* private fields */ }

A HangingGetInner object manages some internal state S and notifies observers of type O when their view of the state is outdated.

While it can be used directly, most API consumers will want to use the higher level HangingGet object. HangingGet and its companion types provide Send for use from multiple threads or async tasks.

Type parameters

• K - the Key by which Observers are identified.
• For other type args see HangingGet.

Implementations

impl<S, K, O, F> HangingGetInner<S, K, O, F>

where K: Eq + Hash, F: Fn(&S, O) -> bool,

pub fn new(state: Option<S>, notify: F) -> Self

Create a new HangingGetInner. state is the initial state of the HangingGetInner notify is a Fn that is used to notify observers of state.

pub fn set(&mut self, state: S)

Set the internal state value to state and notify all observers. Note that notification is not conditional on the value set by calling the set function. Notification will occur regardless of whether the state value differs from the value currently stored by HangingGetInner.

pub fn update(&mut self, state_update: impl FnOnce(&mut Option<S>) -> bool)

Modify the internal state in-place using the state_update function. Notify all observers if state_update returns true.

pub fn subscribe( &mut self, key: K, observer: O ) -> Result<(), HangingGetServerError>

Register an observer as a subscriber of the state.

Observers are grouped by key and all observers will the same key are assumed to have received the latest state update. If an observer with a previously unseen key subscribes, it is immediately notified to the stated. If an observer with a known key subscribes, it will only be notified when the state is updated since last sent to an observer with the same key. All unresolved observers will be resolved to the same value immediately after the state is updated. If there is no stored state, then the notification will be delayed until an update is made.

pub fn unsubscribe(&mut self, key: K)

Deregister all observers that subscribed with key. If an observer is subsequently subscribed with the same key value, it will be treated as a previously unseen key.