Struct HangingGet

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

Deprecated: New code should use [async_utils::hanging_get::server::HangingGet].

TODO(https://fxbug.dev/42055741): Remove this struct.

A HangingGet object manages some internal state S and notifies observers of type O when their view of the state is outdated.

S - the type of State to be watched O - the type of Observers of S F - the type of observer notification behavior, where F: Fn(&S, O) K - the Key by which Observers are identified

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

Implementations

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

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

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

Create a new HangingGet. state is the initial state of the HangingGet 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 HangingGet.

pub fn update(&mut self, state_update: impl FnOnce(&mut 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.

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.