Struct LookupHandler

pub struct LookupHandler<K, V, E> {
    pub map: Arc<Mutex<HashMap<K, SenderList<V, E>>>>,
    /* private fields */
}

LookupHandler provides ability to queue multiple async requests for the same key into a group of futures that resolve upon request completion.

To use LookupHandler, you need to create a custom lookup function. The example below declares a function lookup() that uses LookupHandler to queue requests and if there are no pending requests (request is new) performs the actual request by calling lookup_impl(). The LookupHandler::complete() will resolve all pending futures for the specific key.

Example:

...
pub lookup_handler : LookupHandler<Pubkey,Arc<Data>,Error>
...
async fn lookup(&self, pubkey:&Pubkey) -> Result<Option<Arc<Data>>> {
    let request_type = self.lookup_handler.queue(pubkey).await;
    let result = match request_type {
        RequestType::New(receiver) => {
            // execute the actual lookup
            let response = self.lookup_impl(pubkey).await;
            // signal completion for all awaiting futures
            lookup_handler.complete(pubkey, response).await;
            // this request is queued like all the others
            // so wait for your own notification as well
            receiver.recv().await?
        },
        RequestType::Pending(receiver) => {
            receiver.recv().await?
        }
    }
};

Fields

map: Arc<Mutex<HashMap<K, SenderList<V, E>>>>

Implementations

impl<K, V, E> LookupHandler<K, V, E>

where V: Clone, K: Clone + Eq + Hash + Debug, E: Clone,

pub fn new() -> Self

Create a new instance of the LookupHandler

pub fn pending(&self) -> usize

Returns the total number of pending requests

pub async fn queue(&self, key: &K) -> RequestType<V, E>

Queue the request for key K. Returns RequestType::New if no other requests for the same key are pending and RequestType::Pending if there are pending requests. Both RequestType values contain a async_std::channel::Receiver that can be listened to for lookup completion. Lookup completion can be signaled by LookupHandler::complete()

pub async fn complete(&self, key: &K, result: LookupResult<V, E>)

Signal the lookup completion for key K by supplying a LookupResult with a resulting value V or an error E.

Trait Implementations

impl<K, V, E> Default for LookupHandler<K, V, E>

where V: Clone, K: Clone + Eq + Hash + Debug, E: Clone,

Default trait for the LookupHandler

fn default() -> Self

Returns the “default value” for a type.