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Optimize LRUCache by using a VecDeque.

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We also reverse the order, so that we don't need iter.rev().
This commit is contained in:
Bobby Holley 2017-04-13 16:57:51 +08:00
parent a52d5fbced
commit a32596131a
1 changed files with 17 additions and 15 deletions
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32
components/style/cache.rs
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@ -6,27 +6,28 @@
#![deny(missing_docs)] #![deny(missing_docs)]
use std::{iter, slice}; use std::collections::VecDeque;
use std::collections::vec_deque;
/// A LRU cache used to store a set of at most `n` elements at the same time. /// A LRU cache used to store a set of at most `n` elements at the same time.
/// ///
/// Currently used for the style sharing candidate cache. /// The most-recently-used entry is at index zero.
pub struct LRUCache<K> { pub struct LRUCache<K> {
entries: Vec<K>, entries: VecDeque<K>,
cache_size: usize, cache_size: usize,
} }
/// A iterator over the items of the LRU cache. /// A iterator over the items of the LRU cache.
pub type LRUCacheIterator<'a, K> = iter::Rev<slice::Iter<'a, K>>; pub type LRUCacheIterator<'a, K> = vec_deque::Iter<'a, K>;
/// A iterator over the mutable items of the LRU cache. /// A iterator over the mutable items of the LRU cache.
pub type LRUCacheMutIterator<'a, K> = iter::Rev<slice::IterMut<'a, K>>; pub type LRUCacheMutIterator<'a, K> = vec_deque::IterMut<'a, K>;
impl<K: PartialEq> LRUCache<K> { impl<K: PartialEq> LRUCache<K> {
/// Create a new LRU cache with `size` elements at most. /// Create a new LRU cache with `size` elements at most.
pub fn new(size: usize) -> Self { pub fn new(size: usize) -> Self {
LRUCache { LRUCache {
entries: vec![], entries: VecDeque::with_capacity(size),
cache_size: size, cache_size: size,
} }
} }
@ -37,32 +38,33 @@ impl<K: PartialEq> LRUCache<K> {
} }
#[inline] #[inline]
/// Touch a given position, and put it in the last item on the list. /// Touch a given entry, putting it first in the list.
pub fn touch(&mut self, pos: usize) { pub fn touch(&mut self, pos: usize) {
let last_index = self.entries.len() - 1; let last_index = self.entries.len() - 1;
if pos != last_index { if pos != last_index {
let entry = self.entries.remove(pos); let entry = self.entries.remove(pos).unwrap();
self.entries.push(entry); self.entries.push_front(entry);
} }
} }
/// Iterate over the contents of this cache, from more to less recently /// Iterate over the contents of this cache, from more to less recently
/// used. /// used.
pub fn iter(&self) -> LRUCacheIterator<K> { pub fn iter(&self) -> vec_deque::Iter<K> {
self.entries.iter().rev() self.entries.iter()
} }
/// Iterate mutably over the contents of this cache. /// Iterate mutably over the contents of this cache.
pub fn iter_mut(&mut self) -> LRUCacheMutIterator<K> { pub fn iter_mut(&mut self) -> vec_deque::IterMut<K> {
self.entries.iter_mut().rev() self.entries.iter_mut()
} }
/// Insert a given key in the cache. /// Insert a given key in the cache.
pub fn insert(&mut self, key: K) { pub fn insert(&mut self, key: K) {
if self.entries.len() == self.cache_size { if self.entries.len() == self.cache_size {
self.entries.remove(0); self.entries.pop_back();
} }
self.entries.push(key); self.entries.push_front(key);
debug_assert!(self.entries.len() <= self.cache_size);
} }
/// Evict all elements from the cache. /// Evict all elements from the cache.