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use std::hash::Hash;
use futures::Future;
use tokio::task::JoinHandle;
use crate::cache_api::{CacheResult, CacheLoadingError, CacheEntry};
use crate::backing::CacheBacking;
pub(crate) enum CacheAction<K, V> {
GetIfPresent(K),
Get(K),
Set(K, V),
Update(K, Box<dyn FnOnce(V) -> V + Send + 'static>),
Remove(K),
SetAndUnblock(K, V),
Unblock(K),
}
pub(crate) struct CacheMessage<K, V> {
pub(crate) action: CacheAction<K, V>,
pub(crate) response: tokio::sync::oneshot::Sender<CacheResult<V>>,
}
pub(crate) struct InternalCacheStore<K, V, T, B> {
tx: tokio::sync::mpsc::Sender<CacheMessage<K, V>>,
data: B,
loader: T,
}
impl<
K: Eq + Hash + Clone + Send + 'static,
V: Clone + Sized + Send + 'static,
F: Future<Output=Option<V>> + Sized + Send + 'static,
T: Fn(K) -> F + Send + 'static,
B: CacheBacking<K, CacheEntry<V>> + Send + 'static
> InternalCacheStore<K, V, T, B>
{
pub fn new(
backing: B,
tx: tokio::sync::mpsc::Sender<CacheMessage<K, V>>,
loader: T,
) -> Self {
Self {
tx,
data: backing,
loader,
}
}
pub(crate) fn run(mut self, mut rx: tokio::sync::mpsc::Receiver<CacheMessage<K, V>>) -> JoinHandle<()> {
tokio::spawn(async move {
loop {
if let Some(message) = rx.recv().await {
let result = match message.action {
CacheAction::GetIfPresent(key) => self.get_if_present(key),
CacheAction::Get(key) => self.get(key),
CacheAction::Set(key, value) => self.set(key, value, false),
CacheAction::Update(key, update_fn) => self.update(key, update_fn),
CacheAction::Remove(key) => self.remove(key),
CacheAction::SetAndUnblock(key, value) => self.set(key, value, true),
CacheAction::Unblock(key) => {
self.unblock(key);
CacheResult::None
}
};
message.response.send(result).ok();
}
}
})
}
fn unblock(&mut self, key: K) {
if let Some(entry) = self.data.get(&key) {
if let CacheEntry::Loading(waiter) = entry {
waiter.send(None).ok();
self.data.remove(&key);
}
}
}
fn remove(&mut self, key: K) -> CacheResult<V> {
if let Some(entry) = self.data.remove(&key) {
match entry {
CacheEntry::Loaded(data) => CacheResult::Found(data),
CacheEntry::Loading(_) => CacheResult::None
}
} else {
CacheResult::None
}
}
fn update(&mut self, key: K, update_fn: Box<dyn FnOnce(V) -> V + Send + 'static>) -> CacheResult<V> {
match self.get(key.clone()) {
CacheResult::Found(data) => {
let updated_data = update_fn(data);
self.data.set(key, CacheEntry::Loaded(updated_data.clone()));
CacheResult::Found(updated_data)
}
CacheResult::Loading(handle) => {
CacheResult::Loading(tokio::spawn(async move {
handle.await.unwrap()
}))
}
CacheResult::None => CacheResult::None
}
}
fn set(&mut self, key: K, value: V, loading_result: bool) -> CacheResult<V> {
let opt_entry = self.data.get(&key);
if loading_result {
if opt_entry.is_none() {
return CacheResult::None;
}
let entry = opt_entry.unwrap();
if matches!(entry, CacheEntry::Loaded(_)) {
return CacheResult::None;
}
}
self.data.set(key, CacheEntry::Loaded(value))
.and_then(|entry| {
match entry {
CacheEntry::Loaded(data) => Some(data),
CacheEntry::Loading(_) => None
}
})
.map(|value| CacheResult::Found(value))
.unwrap_or(CacheResult::None)
}
fn get_if_present(&mut self, key: K) -> CacheResult<V> {
if let Some(entry) = self.data.get(&key) {
match entry {
CacheEntry::Loaded(data) => CacheResult::Found(data.clone()),
CacheEntry::Loading(_) => CacheResult::None,
}
} else {
CacheResult::None
}
}
fn get(&mut self, key: K) -> CacheResult<V> {
if let Some(entry) = self.data.get(&key) {
match entry {
CacheEntry::Loaded(value) => {
CacheResult::Found(value.clone())
}
CacheEntry::Loading(waiter) => {
let waiter = waiter.clone();
CacheResult::Loading(tokio::spawn(async move {
if let Ok(result) = waiter.subscribe().recv().await {
if let Some(data) = result {
Ok(data)
} else {
Err(CacheLoadingError { reason_phrase: "Loader function returned None".to_owned() })
}
} else {
Err(CacheLoadingError { reason_phrase: "Waiter broadcast channel error".to_owned() })
}
}))
}
}
} else {
let (tx, _) = tokio::sync::broadcast::channel(1);
let inner_tx = tx.clone();
let cache_tx = self.tx.clone();
let loader = (self.loader)(key.clone());
let inner_key = key.clone();
let join_handle = tokio::spawn(async move {
if let Some(value) = loader.await {
inner_tx.send(Some(value.clone())).ok();
let (tx, rx) = tokio::sync::oneshot::channel();
let send_value = value.clone();
cache_tx.send(CacheMessage {
action: CacheAction::SetAndUnblock(inner_key, send_value),
response: tx,
}).await.ok();
rx.await.ok();
Ok(value)
} else {
inner_tx.send(None).ok();
let (tx, rx) = tokio::sync::oneshot::channel();
cache_tx.send(CacheMessage {
action: CacheAction::Unblock(inner_key),
response: tx,
}).await.ok();
rx.await.ok();
Err(CacheLoadingError { reason_phrase: "Loader function returned None".to_owned() })
}
});
self.data.set(key, CacheEntry::Loading(tx));
CacheResult::Loading(join_handle)
}
}
}