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use std::borrow::Borrow;
use std::collections::HashMap;
use std::hash::Hash;
use std::mem;
use std::sync::{RwLock, RwLockReadGuard, RwLockWriteGuard};
struct Inner<K> {
prev: Option<K>,
next: Option<K>,
}
struct Item<K> {
inner: RwLock<Inner<K>>,
}
impl<K> Item<K> {
fn read(&self) -> RwLockReadGuard<Inner<K>> {
self.inner.read().expect("item")
}
fn write(&self) -> RwLockWriteGuard<Inner<K>> {
self.inner.write().expect("item")
}
}
pub struct State<K> {
cache: HashMap<K, Item<K>>,
first: Option<K>,
last: Option<K>,
}
impl<K: Clone + Eq + Hash> State<K> {
fn bump(&mut self, key: K) {
let mut item = if let Some(item) = self.cache.get(&key) {
item.write()
} else {
return;
};
let last = if item.next.is_none() {
return;
} else if item.prev.is_none() && item.next.is_some() {
let next_key = item.next.as_ref().expect("next key");
let mut next = self.cache.get(next_key).expect("next item").write();
mem::swap(&mut next.prev, &mut item.prev); mem::swap(&mut item.next, &mut next.next); mem::swap(&mut item.prev, &mut next.next); item.prev.clone()
} else {
let prev_key = item.prev.as_ref().expect("previous key");
let mut prev = self.cache.get(prev_key).expect("previous item").write();
let next_key = item.next.as_ref().expect("next key").clone();
let mut next = self.cache.get(&next_key).expect("next item").write();
mem::swap(&mut prev.next, &mut item.next); mem::swap(&mut item.next, &mut next.next); mem::swap(&mut next.prev, &mut item.prev); item.prev = Some(next_key); None
};
let first = if let Some(next_key) = &item.next {
let mut skip = self.cache.get(next_key).expect("skipped item").write();
skip.prev = Some(key);
None
} else {
Some(key)
};
match (last, first) {
(Some(last), None) => self.last = Some(last),
(None, Some(first)) => self.first = Some(first),
(Some(last), Some(first)) => {
self.last = Some(last);
self.first = Some(first);
}
(None, None) => {}
}
}
fn pop(&mut self) -> Option<K> {
let last = self.last.as_ref()?;
let (key, item) = self.cache.remove_entry(last).expect("last entry");
self.remove_inner(item);
Some(key)
}
fn remove_inner(&mut self, item: Item<K>) {
let mut inner = item.write();
if inner.prev.is_none() && inner.next.is_none() {
self.last = None;
self.first = None;
} else if inner.prev.is_none() {
self.last = inner.next.clone();
let next_key = inner.next.as_ref().expect("next key");
let mut next = self.cache.get(&*next_key).expect("next item").write();
mem::swap(&mut next.prev, &mut inner.prev);
} else if inner.next.is_none() {
self.first = inner.prev.clone();
let prev_key = inner.prev.as_ref().expect("previous key");
let mut prev = self.cache.get(prev_key).expect("previous item").write();
mem::swap(&mut prev.next, &mut inner.next);
} else {
let prev_key = inner.prev.as_ref().expect("previous key");
let mut prev = self.cache.get(prev_key).expect("previous item").write();
let next_key = inner.next.as_ref().expect("next key");
let mut next = self.cache.get(&*next_key).expect("next item").write();
mem::swap(&mut next.prev, &mut inner.prev);
mem::swap(&mut prev.next, &mut inner.next);
}
}
fn remove(&mut self, key: &K) -> Option<K> {
if let Some((key, item)) = self.cache.remove_entry(key) {
self.remove_inner(item);
Some(key)
} else {
None
}
}
}
pub struct LFUCache<K> {
state: RwLock<State<K>>,
}
impl<K: Clone + Eq + Hash> LFUCache<K> {
pub fn new() -> Self {
let state = State {
cache: HashMap::new(),
first: None,
last: None,
};
Self {
state: RwLock::new(state),
}
}
pub fn contains_key<Q: ?Sized>(&self, key: &Q) -> bool
where
K: Borrow<Q>,
Q: Hash + Eq,
{
let state = self.state.read().expect("LFU read lock");
state.cache.contains_key(key)
}
pub fn insert(&self, key: K) -> bool {
let mut state = self.state.write().expect("LFU write lock");
if state.cache.contains_key(&key) {
state.bump(key);
true
} else {
let prev = None;
let mut next = Some(key.clone());
mem::swap(&mut state.last, &mut next);
if let Some(next_key) = &next {
let mut next = state.cache.get(next_key).expect("next item").write();
next.prev = Some(key.clone());
}
if state.first.is_none() {
state.first = Some(key.clone());
}
let item = Item {
inner: RwLock::new(Inner { prev, next }),
};
state.cache.insert(key, item);
false
}
}
pub fn is_empty(&self) -> bool {
self.state.read().expect("LFU cache state").cache.is_empty()
}
pub fn iter(&self) -> Iter<K> {
let state = self.state.read().expect("LFU cache");
let current = state.last.clone();
Iter { state, current }
}
pub fn len(&self) -> usize {
self.state.read().expect("LFU cache state").cache.len()
}
pub fn pop(&self) -> Option<K> {
let mut state = self.state.write().expect("LFU cache state");
state.pop()
}
pub fn remove(&self, key: &K) -> Option<K> {
let mut state = self.state.write().expect("LFU cache state");
state.remove(key)
}
}
pub struct Iter<'a, K> {
state: RwLockReadGuard<'a, State<K>>,
current: Option<K>,
}
impl<'a, K: Clone + Eq + Hash> Iterator for Iter<'a, K> {
type Item = K;
fn next(&mut self) -> Option<Self::Item> {
if let Some(key) = &mut self.current {
let item = self.state.cache.get(key).expect("LFU cache item");
let mut next = item.read().next.clone();
mem::swap(&mut self.current, &mut next);
next
} else {
None
}
}
}
#[cfg(test)]
mod tests {
use std::fmt;
use rand::{thread_rng, Rng};
use super::*;
#[allow(dead_code)]
fn print_debug<K: fmt::Display + Clone + Eq + Hash>(cache: &LFUCache<K>) {
let state = cache.state.read().expect("LFU cache state");
let mut next = state.last.clone();
while let Some(next_key) = next {
let item = state.cache.get(&next_key).expect("item").read();
if let Some(prev_key) = item.prev.as_ref() {
print!("{}-", prev_key);
}
next = item.next.clone();
if let Some(next_key) = &next {
print!("-{}", next_key);
}
print!(" ");
}
println!();
}
fn validate<K: fmt::Debug + Clone + Eq + Hash>(cache: &LFUCache<K>) {
let state = cache.state.read().expect("LFU cache state");
if state.cache.is_empty() {
assert!(state.first.is_none());
assert!(state.last.is_none());
} else {
let first_key = state.first.as_ref().expect("first key");
let first = state.cache.get(first_key).expect("first item").read();
assert!(first.next.is_none());
let last_key = state.last.as_ref().expect("last key");
let last = state.cache.get(last_key).expect("last item").read();
assert!(last.prev.is_none());
}
let mut last = None;
let mut next = state.last.clone();
while let Some(key) = next {
let item = state.cache.get(&key).expect("item").read();
if let Some(last_key) = &last {
let prev_key = item.prev.as_ref().expect("previous key");
assert_eq!(last_key, prev_key);
}
last = Some(key);
next = item.next.clone();
}
}
#[test]
fn test_order() {
let cache = LFUCache::new();
let expected: Vec<i32> = (0..10).collect();
for i in expected.iter().rev() {
cache.insert(i);
}
let mut actual = Vec::with_capacity(expected.len());
for i in cache.iter() {
actual.push(*i);
}
assert_eq!(actual, expected)
}
#[test]
fn test_access() {
let mut cache = LFUCache::new();
let mut rng = thread_rng();
for _ in 1..100_000 {
let i: i32 = rng.gen_range(0..1000);
cache.insert(i);
validate(&mut cache);
let mut size = 0;
for _ in cache.iter() {
size += 1;
}
assert_eq!(cache.len(), size);
assert!(!cache.is_empty());
let i: i32 = rng.gen_range(0..1000);
cache.remove(&i);
validate(&mut cache);
let mut size = 0;
for _ in cache.iter() {
size += 1;
}
while !cache.is_empty() {
cache.pop();
size -= 1;
assert_eq!(cache.len(), size);
}
assert_eq!(cache.len(), 0);
}
}
}