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use tokio::task::JoinHandle;
use std::hash::Hash;
use futures::Future;
use crate::internal_cache::{CacheAction, InternalCacheStore, CacheMessage};
use crate::backing::{CacheBacking, HashMapBacking};
#[derive(Debug, Clone)]
pub struct CacheLoadingError {
pub reason_phrase: String,
// todo: nested errors
}
#[derive(Debug, Clone)]
pub enum CacheEntry<V> {
Loaded(V),
Loading(tokio::sync::broadcast::Sender<Option<V>>),
}
#[derive(Debug)]
pub enum CacheResult<V> {
Found(V),
Loading(JoinHandle<Result<V, CacheLoadingError>>),
None,
}
pub type CacheHandle = JoinHandle<()>;
#[derive(Debug, Clone)]
pub struct LoadingCache<K, V> {
tx: tokio::sync::mpsc::Sender<CacheMessage<K, V>>
}
impl<
K: Eq + Hash + Clone + Send + 'static,
V: Clone + Sized + Send + 'static,
> LoadingCache<K, V> {
/// Creates a new instance of a LoadingCache
///
/// # Arguments
///
/// * `loader` - A function which returns a Future<Output=Option<V>>
///
/// # Return Value
///
/// This method returns a tuple, with:
/// 0 - The instance of the LoadingCache
/// 1 - The CacheHandle which is a JoinHandle<()> and represents the task which operates
/// the cache
///
/// # Examples
///
/// ```
/// async fn example() {
/// use cache_loader_async::cache_api::LoadingCache;
/// use std::collections::HashMap;
/// let static_db: HashMap<String, u32> =
/// vec![("foo".into(), 32), ("bar".into(), 64)]
/// .into_iter()
/// .collect();
///
/// let (cache, _) = LoadingCache::new(move |key: String| {
/// let db_clone = static_db.clone();
/// async move {
/// db_clone.get(&key).cloned()
/// }
/// });
///
/// let result = cache.get("foo".to_owned()).await.unwrap();
///
/// assert_eq!(result, 32);
/// }
/// ```
pub fn new<T, F>(loader: T) -> (LoadingCache<K, V>, CacheHandle)
where F: Future<Output=Option<V>> + Sized + Send + 'static,
T: Fn(K) -> F + Send + 'static {
LoadingCache::with_backing(HashMapBacking::new(), loader)
}
pub fn with_backing<T, F, B>(backing: B, loader: T) -> (LoadingCache<K, V>, CacheHandle)
where F: Future<Output=Option<V>> + Sized + Send + 'static,
T: Fn(K) -> F + Send + 'static,
B: CacheBacking<K, CacheEntry<V>> + Send + 'static {
let (tx, rx) = tokio::sync::mpsc::channel(128);
let store = InternalCacheStore::new(backing, tx.clone(), loader);
let handle = store.run(rx);
(LoadingCache {
tx
}, handle)
}
/// Retrieves or loads the value for specified key from either cache or loader function
///
/// # Arguments
///
/// * `key` - The key which should be loaded
///
/// # Return Value
///
/// Returns a Result with:
/// Ok - Value of type V
/// Err - Error of type CacheLoadingError
pub async fn get(&self, key: K) -> Result<V, CacheLoadingError> {
self.send_cache_action(CacheAction::Get(key)).await
.map(|opt_result| opt_result.expect("Get should always return either V or CacheLoadingError"))
}
/// Sets the value for specified key and bypasses eventual currently ongoing loads
/// If a key has been set programmatically, eventual concurrent loads will not change
/// the value of the key.
///
/// # Arguments
///
/// * `key` - The key which should be loaded
///
/// # Return Value
///
/// Returns a Result with:
/// Ok - Previous value of type V wrapped in an Option depending whether there was a previous
/// value
/// Err - Error of type CacheLoadingError
pub async fn set(&self, key: K, value: V) -> Result<Option<V>, CacheLoadingError> {
self.send_cache_action(CacheAction::Set(key, value)).await
}
pub async fn get_if_present(&self, key: K) -> Result<Option<V>, CacheLoadingError> {
self.send_cache_action(CacheAction::GetIfPresent(key)).await
}
pub async fn exists(&self, key: K) -> Result<bool, CacheLoadingError> {
self.get_if_present(key).await
.map(|result| result.is_some())
}
pub async fn remove(&self, key: K) -> Result<Option<V>, CacheLoadingError> {
self.send_cache_action(CacheAction::Remove(key)).await
}
/// Unstable, Undocumented & Inconsistent. Don't use that just yet
pub async fn update<U>(&self, key: K, update_fn: U) -> Result<V, CacheLoadingError>
where U: FnOnce(V) -> V + Send + 'static {
self.send_cache_action(CacheAction::Update(key, Box::new(update_fn))).await
.map(|opt_result| opt_result.expect("Get should always return either V or CacheLoadingError"))
}
async fn send_cache_action(&self, action: CacheAction<K, V>) -> Result<Option<V>, CacheLoadingError> {
let (tx, rx) = tokio::sync::oneshot::channel();
match self.tx.send(CacheMessage {
action,
response: tx,
}).await {
Ok(_) => {
match rx.await {
Ok(result) => {
match result {
CacheResult::Found(value) => { Ok(Some(value)) }
CacheResult::Loading(handle) => {
match handle.await {
Ok(load_result) => {
load_result.map(|v| Some(v))
}
Err(_) => {
Err(CacheLoadingError { reason_phrase: "Error when trying to join loader future".to_owned() })
}
}
}
CacheResult::None => { Ok(None) }
}
}
Err(_) => {
Err(CacheLoadingError { reason_phrase: "Error when receiving cache response".to_owned() })
}
}
}
Err(_) => {
Err(CacheLoadingError { reason_phrase: "Error when trying to submit cache request".to_owned() })
}
}
}
}