1 // Copyright 2013 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
12 //! A cache that holds a limited number of key-value pairs. When the
13 //! capacity of the cache is exceeded, the least-recently-used
14 //! (where "used" means a look-up or putting the pair into the cache)
15 //! pair is automatically removed.
20 //! use collections::LruCache;
22 //! let mut cache: LruCache<int, int> = LruCache::new(2);
26 //! assert!(cache.get(&1).is_none());
27 //! assert_eq!(*cache.get(&2).unwrap(), 20);
28 //! assert_eq!(*cache.get(&3).unwrap(), 30);
31 //! assert_eq!(*cache.get(&2).unwrap(), 22);
34 //! assert!(cache.get(&3).is_none());
36 //! cache.change_capacity(1);
37 //! assert!(cache.get(&2).is_none());
41 use std::container::Container;
42 use std::hash::{Hash, sip};
48 struct KeyRef<K> { k: *K }
50 struct LruEntry<K, V> {
53 next: *mut LruEntry<K, V>,
54 prev: *mut LruEntry<K, V>,
58 pub struct LruCache<K, V> {
59 priv map: HashMap<KeyRef<K>, ~LruEntry<K, V>>,
61 priv head: *mut LruEntry<K, V>,
62 priv tail: *mut LruEntry<K, V>,
65 impl<K: Hash> Hash for KeyRef<K> {
66 fn hash(&self, s: &mut sip::SipState) {
67 unsafe {(*self.k).hash(s)}
71 impl<K: Eq> Eq for KeyRef<K> {
72 fn eq(&self, other: &KeyRef<K>) -> bool {
73 unsafe{ (*self.k).eq(&*other.k) }
77 impl<K, V> LruEntry<K, V> {
78 fn new() -> LruEntry<K, V> {
82 next: ptr::mut_null(),
83 prev: ptr::mut_null(),
87 fn with_key_value(k: K, v: V) -> LruEntry<K, V> {
91 next: ptr::mut_null(),
92 prev: ptr::mut_null(),
97 impl<K: Hash + Eq, V> LruCache<K, V> {
98 /// Create an LRU Cache that holds at most `capacity` items.
99 pub fn new(capacity: uint) -> LruCache<K, V> {
100 let cache = LruCache {
103 head: unsafe{ cast::transmute(~LruEntry::<K, V>::new()) },
104 tail: unsafe{ cast::transmute(~LruEntry::<K, V>::new()) },
107 (*cache.head).next = cache.tail;
108 (*cache.tail).prev = cache.head;
113 /// Put a key-value pair into cache.
114 pub fn put(&mut self, k: K, v: V) {
115 let mut key_existed = false;
116 let (node_ptr, node_opt) = match self.map.find_mut(&KeyRef{k: &k}) {
119 node.value = Some(v);
120 let node_ptr: *mut LruEntry<K, V> = &mut **node;
124 let mut node = ~LruEntry::with_key_value(k, v);
125 let node_ptr: *mut LruEntry<K, V> = &mut *node;
126 (node_ptr, Some(node))
130 self.detach(node_ptr);
131 self.attach(node_ptr);
133 let keyref = unsafe { (*node_ptr).key.as_ref().unwrap() };
134 self.map.swap(KeyRef{k: keyref}, node_opt.unwrap());
135 self.attach(node_ptr);
136 if self.len() > self.capacity() {
142 /// Return a value corresponding to the key in the cache.
143 pub fn get<'a>(&'a mut self, k: &K) -> Option<&'a V> {
144 let (value, node_ptr_opt) = match self.map.find_mut(&KeyRef{k: k}) {
145 None => (None, None),
147 let node_ptr: *mut LruEntry<K, V> = &mut **node;
149 match (*node_ptr).value {
150 None => (None, None),
151 Some(ref value) => (Some(value), Some(node_ptr))
159 self.detach(node_ptr);
160 self.attach(node_ptr);
166 /// Remove and return a value corresponding to the key from the cache.
167 pub fn pop(&mut self, k: &K) -> Option<V> {
168 match self.map.pop(&KeyRef{k: k}) {
170 Some(lru_entry) => lru_entry.value
174 /// Return the maximum number of key-value pairs the cache can hold.
175 pub fn capacity(&self) -> uint {
179 /// Change the number of key-value pairs the cache can hold. Remove
180 /// least-recently-used key-value pairs if necessary.
181 pub fn change_capacity(&mut self, capacity: uint) {
182 for _ in range(capacity, self.len()) {
185 self.max_size = capacity;
189 fn remove_lru(&mut self) {
191 let lru = unsafe { (*self.tail).prev };
196 Some(ref k) => { self.map.pop(&KeyRef{k: k}); }
203 fn detach(&mut self, node: *mut LruEntry<K, V>) {
205 (*(*node).prev).next = (*node).next;
206 (*(*node).next).prev = (*node).prev;
211 fn attach(&mut self, node: *mut LruEntry<K, V>) {
213 (*node).next = (*self.head).next;
214 (*node).prev = self.head;
215 (*self.head).next = node;
216 (*(*node).next).prev = node;
221 impl<A: fmt::Show + Hash + Eq, B: fmt::Show> fmt::Show for LruCache<A, B> {
222 /// Return a string that lists the key-value pairs from most-recently
223 /// used to least-recently used.
224 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
225 try!(write!(f.buf, r"\{"));
226 let mut cur = self.head;
227 for i in range(0, self.len()) {
228 if i > 0 { try!(write!(f.buf, ", ")) }
232 // should never print nil
233 None => try!(write!(f.buf, "nil")),
234 Some(ref k) => try!(write!(f.buf, "{}", *k)),
237 try!(write!(f.buf, ": "));
240 // should never print nil
241 None => try!(write!(f.buf, "nil")),
242 Some(ref value) => try!(write!(f.buf, "{}", *value)),
250 impl<K: Hash + Eq, V> Container for LruCache<K, V> {
251 /// Return the number of key-value pairs in the cache.
252 fn len(&self) -> uint {
257 impl<K: Hash + Eq, V> Mutable for LruCache<K, V> {
258 /// Clear the cache of all key-value pairs.
259 fn clear(&mut self) {
265 impl<K, V> Drop for LruCache<K, V> {
268 let _: ~LruEntry<K, V> = cast::transmute(self.head);
269 let _: ~LruEntry<K, V> = cast::transmute(self.tail);
278 fn assert_opt_eq<V: Eq>(opt: Option<&V>, v: V) {
279 assert!(opt.is_some());
280 assert_eq!(opt.unwrap(), &v);
284 fn test_put_and_get() {
285 let mut cache: LruCache<int, int> = LruCache::new(2);
288 assert_opt_eq(cache.get(&1), 10);
289 assert_opt_eq(cache.get(&2), 20);
290 assert_eq!(cache.len(), 2);
294 fn test_put_update() {
295 let mut cache: LruCache<~str, ~[u8]> = LruCache::new(1);
296 cache.put(~"1", ~[10, 10]);
297 cache.put(~"1", ~[10, 19]);
298 assert_opt_eq(cache.get(&~"1"), ~[10, 19]);
299 assert_eq!(cache.len(), 1);
303 fn test_expire_lru() {
304 let mut cache: LruCache<~str, ~str> = LruCache::new(2);
305 cache.put(~"foo1", ~"bar1");
306 cache.put(~"foo2", ~"bar2");
307 cache.put(~"foo3", ~"bar3");
308 assert!(cache.get(&~"foo1").is_none());
309 cache.put(~"foo2", ~"bar2update");
310 cache.put(~"foo4", ~"bar4");
311 assert!(cache.get(&~"foo3").is_none());
316 let mut cache: LruCache<int, int> = LruCache::new(2);
319 assert_eq!(cache.len(), 2);
320 let opt1 = cache.pop(&1);
321 assert!(opt1.is_some());
322 assert_eq!(opt1.unwrap(), 10);
323 assert!(cache.get(&1).is_none());
324 assert_eq!(cache.len(), 1);
328 fn test_change_capacity() {
329 let mut cache: LruCache<int, int> = LruCache::new(2);
330 assert_eq!(cache.capacity(), 2);
333 cache.change_capacity(1);
334 assert!(cache.get(&1).is_none());
335 assert_eq!(cache.capacity(), 1);
340 let mut cache: LruCache<int, int> = LruCache::new(3);
344 assert_eq!(cache.to_str(), ~"{3: 30, 2: 20, 1: 10}");
346 assert_eq!(cache.to_str(), ~"{2: 22, 3: 30, 1: 10}");
348 assert_eq!(cache.to_str(), ~"{6: 60, 2: 22, 3: 30}");
350 assert_eq!(cache.to_str(), ~"{3: 30, 6: 60, 2: 22}");
351 cache.change_capacity(2);
352 assert_eq!(cache.to_str(), ~"{3: 30, 6: 60}");
357 let mut cache: LruCache<int, int> = LruCache::new(2);
361 assert!(cache.get(&1).is_none());
362 assert!(cache.get(&2).is_none());
363 assert_eq!(cache.to_str(), ~"{}");