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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 with the default `HashMapBacking` /// /// # 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 /// /// ``` /// use cache_loader_async::cache_api::LoadingCache; /// use std::collections::HashMap; /// async fn example() { /// 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) } /// Creates a new instance of a LoadingCache with a custom `CacheBacking` /// /// # Arguments /// /// * `backing` - The custom backing which the cache should use /// * `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 /// /// ``` /// use cache_loader_async::cache_api::LoadingCache; /// use std::collections::HashMap; /// use cache_loader_async::backing::HashMapBacking; /// async fn example() { /// let static_db: HashMap<String, u32> = /// vec![("foo".into(), 32), ("bar".into(), 64)] /// .into_iter() /// .collect(); /// /// let (cache, _) = LoadingCache::with_backing( /// HashMapBacking::new(), // this is the default implementation of `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 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 } /// Loads the value for the specified key from the cache and returns None if not present /// /// # Arguments /// /// * `key` - The key which should be loaded /// /// # Return Value /// /// Returns a Result with: /// Ok - Value of type Option<V> /// Err - Error of type CacheLoadingError pub async fn get_if_present(&self, key: K) -> Result<Option<V>, CacheLoadingError> { self.send_cache_action(CacheAction::GetIfPresent(key)).await } /// Checks whether a specific value is mapped for the given key /// /// # Arguments /// /// * `key` - The key which should be checked /// /// # Return Value /// /// Returns a Result with: /// Ok - bool /// Err - Error of type CacheLoadingError pub async fn exists(&self, key: K) -> Result<bool, CacheLoadingError> { self.get_if_present(key).await .map(|result| result.is_some()) } /// Removes a specific key-value mapping from the cache and returns the previous result /// if there was any or None /// /// # Arguments /// /// * `key` - The key which should be evicted /// /// # Return Value /// /// Returns a Result with: /// Ok - Value of type Option<V> /// Err - Error of type CacheLoadingError pub async fn remove(&self, key: K) -> Result<Option<V>, CacheLoadingError> { self.send_cache_action(CacheAction::Remove(key)).await } /// Updates a key on the cache with the given update function and returns the previous value /// /// If the key is not present yet, it'll be loaded using the loader function and will be /// updated once this loader function completes. /// In case the key was manually updated via `set` during the loader function the update will /// take place on the manually updated value, so user-controlled input takes precedence over /// the loader function /// /// # Arguments /// /// * `key` - The key which should be updated /// * `update_fn` - A `FnOnce(V) -> V` which has the current value as parameter and should /// return the updated value /// /// # Return Value /// /// Returns a Result with: /// Ok - Value of type V which is the previously mapped value /// Err - Error of type CacheLoadingError 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() }) } } } }