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use std::collections::{VecDeque, HashSet};
use std::hash::Hash;
const COLLECTION_QUEUE_SIZE: usize = 8;
pub struct CacheManager<T> where T: Eq + Hash {
pref_cache_size: usize,
max_cache_size: usize,
bytes_per_cache_entry: usize,
cache_usage: VecDeque<HashSet<T>>
}
impl<T> CacheManager<T> where T: Eq + Hash {
pub fn new(pref_cache_size: usize, max_cache_size: usize, bytes_per_cache_entry: usize) -> Self {
CacheManager {
pref_cache_size: pref_cache_size,
max_cache_size: max_cache_size,
bytes_per_cache_entry: bytes_per_cache_entry,
cache_usage: (0..COLLECTION_QUEUE_SIZE).into_iter().map(|_| Default::default()).collect(),
}
}
pub fn note_used(&mut self, id: T) {
if !self.cache_usage[0].contains(&id) {
if let Some(c) = self.cache_usage.iter_mut().skip(1).find(|e| e.contains(&id)) {
c.remove(&id);
}
self.cache_usage[0].insert(id);
}
}
pub fn collect_garbage<F>(&mut self, current_size: usize, mut notify_unused: F) where F: FnMut(HashSet<T>) -> usize {
if current_size < self.pref_cache_size {
self.rotate_cache_if_needed();
return;
}
for _ in 0..COLLECTION_QUEUE_SIZE {
if let Some(back) = self.cache_usage.pop_back() {
let current_size = notify_unused(back);
self.cache_usage.push_front(Default::default());
if current_size < self.max_cache_size {
break
}
}
}
}
fn rotate_cache_if_needed(&mut self) {
if self.cache_usage.is_empty() { return }
if self.cache_usage[0].len() * self.bytes_per_cache_entry > self.pref_cache_size / COLLECTION_QUEUE_SIZE {
if let Some(cache) = self.cache_usage.pop_back() {
self.cache_usage.push_front(cache);
}
}
}
}