Function read 

pub fn read<K, T, E, F>(
    owner: &OwnerHandle,
    key: impl Fn() -> K + 'static,
    load: impl Fn(K, CancellationToken) -> F + 'static,
) -> AsyncValue<K, T, E>
where
    K: Clone + PartialEq + 'static,
    T: 'static,
    E: Display + 'static,
    F: Future<Output = Result<T, E>> + 'static,

Declare a read participating in the nearest generated coherent region.