Struct Fetcher

pub struct Fetcher<T, C> {
    in_progress: Arc<Mutex<HashMap<T, BTreeSet<C>>>>,
    backoff: ExponentialBackoff,
    permit: Arc<Semaphore>,
}

Management of concurrent requests to fetch resources.

Fields

in_progress: Arc<Mutex<HashMap<T, BTreeSet<C>>>>

backoff: ExponentialBackoff

permit: Arc<Semaphore>

Implementations

impl<T, C> Fetcher<T, C>

pub fn new(permit: Arc<Semaphore>, backoff: ExponentialBackoff) -> Self

impl<T, C> Fetcher<T, C>

pub fn spawn_fetch<Types>( &self, req: T, provider: impl Provider<Types, T> + 'static, callbacks: impl IntoIterator<Item = C> + Send + 'static, )

where T: Request<Types> + 'static, C: Callback<T::Response> + 'static,

Fetch a resource, if it is not already being fetched.

This function will spawn a new task to fetch the resource in the background, using callbacks to process the fetched resource upon success. If the resource is already being fetched, the spawned task will terminate without fetching the resource, but only after registering the provided callbacks to be executed by the existing fetching task upon completion, as long as there are not already equivalent callbacks registered.

We spawn a (short-lived) task even if the resource is already being fetched, because the check that the resource is being fetched requires an exclusive lock, and we do not want to block the caller, which might be on the critical path of request handling.

Note that while callbacks are allowed to be async, they are executed sequentially while an exclusive lock is held, and thus they should not take too long to run or block indefinitely.

The spawned task will continue trying to fetch the object until it succeeds, so it is the caller’s responsibility only to use this method for resources which are known to exist and be fetchable by provider.

Trait Implementations

impl<T, C> Clone for Fetcher<T, C>

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T, C> Debug for Fetcher<T, C>

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

Formats the value using the given formatter.