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use lru::LruCache;
use std::hash::Hash;
const INITIAL_CAPACITY: usize = 4;
pub trait ResidentSize {
fn resident_size(&self) -> usize;
}
pub struct MemoryLruCache<K, V> {
inner: LruCache<K, V>,
cur_size: usize,
max_size: usize,
}
impl<K: Eq + Hash, V: ResidentSize> MemoryLruCache<K, V> {
pub fn new(max_size: usize) -> Self {
MemoryLruCache {
inner: LruCache::new(INITIAL_CAPACITY),
max_size: max_size,
cur_size: 0,
}
}
pub fn insert(&mut self, key: K, val: V) {
let cap = self.inner.cap();
if self.inner.len() == cap && self.cur_size < self.max_size {
self.inner.resize(cap * 2);
}
self.cur_size += val.resident_size();
if let Some(lru) = self.inner.put(key, val) {
self.cur_size -= lru.resident_size();
}
self.readjust_down();
}
pub fn get(&mut self, key: &K) -> Option<&V> {
self.inner.get(key)
}
pub fn with_mut<U>(&mut self, key: &K, with: impl FnOnce(Option<&mut V>) -> U) -> U {
let mut val = self.inner.get_mut(key);
let prev_size = val.as_ref().map_or(0, |v| v.resident_size());
let res = with(val.as_mut().map(|v: &mut &mut V| &mut **v));
let new_size = val.as_ref().map_or(0, |v| v.resident_size());
self.cur_size -= prev_size;
self.cur_size += new_size;
self.readjust_down();
res
}
pub fn current_size(&self) -> usize {
self.cur_size
}
fn readjust_down(&mut self) {
while self.cur_size > self.max_size {
match self.inner.pop_lru() {
Some((_, v)) => self.cur_size -= v.resident_size(),
_ => break,
}
}
}
}
#[cfg(test)]
mod tests {
use super::*;
impl ResidentSize for Vec<u8> {
fn resident_size(&self) -> usize {
self.len()
}
}
#[test]
fn it_works() {
let mut cache = MemoryLruCache::new(256);
let val1 = vec![0u8; 100];
let size1 = val1.resident_size();
cache.insert("hello", val1);
assert_eq!(cache.current_size(), size1);
let val2 = vec![0u8; 210];
let size2 = val2.resident_size();
cache.insert("world", val2);
assert!(cache.get(&"hello").is_none());
assert!(cache.get(&"world").is_some());
assert_eq!(cache.current_size(), size2);
}
}