diff --git a/src/libextra/lib.rs b/src/libextra/lib.rs
index 106dc5bf5c9da..733795fc1f796 100644
--- a/src/libextra/lib.rs
+++ b/src/libextra/lib.rs
@@ -71,6 +71,7 @@ pub mod sort;
pub mod dlist;
pub mod treemap;
pub mod btree;
+pub mod lru_cache;
// And ... other stuff
diff --git a/src/libextra/lru_cache.rs b/src/libextra/lru_cache.rs
new file mode 100644
index 0000000000000..ff8748e1946c1
--- /dev/null
+++ b/src/libextra/lru_cache.rs
@@ -0,0 +1,365 @@
+// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+
+//! A cache that holds a limited number of key-value pairs. When the
+//! capacity of the cache is exceeded, the least-recently-used
+//! (where "used" means a look-up or putting the pair into the cache)
+//! pair is automatically removed.
+//!
+//! # Example
+//!
+//! ```rust
+//! let mut cache: LruCache<int, int> = LruCache::new(2);
+//! cache.put(1, 10);
+//! cache.put(2, 20);
+//! cache.put(3, 30);
+//! assert!(cache.get(&1).is_none());
+//! assert_eq!(*cache.get(&2).unwrap(), 20);
+//! assert_eq!(*cache.get(&3).unwrap(), 30);
+//!
+//! cache.put(2, 22);
+//! assert_eq!(*cache.get(&2).unwrap(), 22);
+//!
+//! cache.put(6, 60);
+//! assert!(cache.get(&3).is_none());
+//!
+//! cache.change_capacity(1);
+//! assert!(cache.get(&2).is_none());
+//! ```
+
+use std::container::Container;
+use std::hashmap::HashMap;
+use std::to_bytes::Cb;
+use std::ptr;
+use std::cast;
+
+struct KeyRef<K> { priv k: *K }
+
+struct LruEntry<K, V> {
+ priv key: Option<K>,
+ priv value: Option<V>,
+ priv next: *mut LruEntry<K, V>,
+ priv prev: *mut LruEntry<K, V>,
+}
+
+/// An LRU Cache.
+pub struct LruCache<K, V> {
+ priv map: HashMap<KeyRef<K>, ~LruEntry<K, V>>,
+ priv max_size: uint,
+ priv head: *mut LruEntry<K, V>,
+ priv tail: *mut LruEntry<K, V>,
+}
+
+impl<K: IterBytes> IterBytes for KeyRef<K> {
+ fn iter_bytes(&self, lsb0: bool, f: Cb) -> bool {
+ unsafe{ (*self.k).iter_bytes(lsb0, f) }
+ }
+}
+
+impl<K: Eq> Eq for KeyRef<K> {
+ fn eq(&self, other: &KeyRef<K>) -> bool {
+ unsafe{ (*self.k).eq(&*other.k) }
+ }
+}
+
+impl<K, V> LruEntry<K, V> {
+ fn new() -> LruEntry<K, V> {
+ LruEntry {
+ key: None,
+ value: None,
+ next: ptr::mut_null(),
+ prev: ptr::mut_null(),
+ }
+ }
+
+ fn with_key_value(k: K, v: V) -> LruEntry<K, V> {
+ LruEntry {
+ key: Some(k),
+ value: Some(v),
+ next: ptr::mut_null(),
+ prev: ptr::mut_null(),
+ }
+ }
+}
+
+impl<K: IterBytes + Eq, V> LruCache<K, V> {
+ /// Create an LRU Cache that holds at most `capacity` items.
+ pub fn new(capacity: uint) -> LruCache<K, V> {
+ let cache = LruCache {
+ map: HashMap::new(),
+ max_size: capacity,
+ head: unsafe{ cast::transmute(~LruEntry::<K, V>::new()) },
+ tail: unsafe{ cast::transmute(~LruEntry::<K, V>::new()) },
+ };
+ unsafe {
+ (*cache.head).next = cache.tail;
+ (*cache.tail).prev = cache.head;
+ }
+ return cache;
+ }
+
+ /// Put a key-value pair into cache.
+ pub fn put(&mut self, k: K, v: V) {
+ let mut key_existed = false;
+ let (node_ptr, node_opt) = match self.map.find_mut(&KeyRef{k: &k}) {
+ Some(node) => {
+ key_existed = true;
+ node.value = Some(v);
+ let node_ptr: *mut LruEntry<K, V> = &mut **node;
+ (node_ptr, None)
+ }
+ None => {
+ let mut node = ~LruEntry::with_key_value(k, v);
+ let node_ptr: *mut LruEntry<K, V> = &mut *node;
+ (node_ptr, Some(node))
+ }
+ };
+ if key_existed {
+ self.detach(node_ptr);
+ self.attach(node_ptr);
+ } else {
+ let keyref = unsafe { (*node_ptr).key.as_ref().unwrap() };
+ self.map.swap(KeyRef{k: keyref}, node_opt.unwrap());
+ self.attach(node_ptr);
+ if self.len() > self.capacity() {
+ self.remove_lru();
+ }
+ }
+ }
+
+ /// Return a value corresponding to the key in the cache.
+ pub fn get<'a>(&'a mut self, k: &K) -> Option<&'a V> {
+ let (value, node_ptr_opt) = match self.map.find_mut(&KeyRef{k: k}) {
+ None => (None, None),
+ Some(node) => {
+ let node_ptr: *mut LruEntry<K, V> = &mut **node;
+ unsafe {
+ match (*node_ptr).value {
+ None => (None, None),
+ Some(ref value) => (Some(value), Some(node_ptr))
+ }
+ }
+ }
+ };
+ match node_ptr_opt {
+ None => (),
+ Some(node_ptr) => {
+ self.detach(node_ptr);
+ self.attach(node_ptr);
+ }
+ }
+ return value;
+ }
+
+ /// Remove and return a value corresponding to the key from the cache.
+ pub fn pop(&mut self, k: &K) -> Option<V> {
+ match self.map.pop(&KeyRef{k: k}) {
+ None => None,
+ Some(lru_entry) => lru_entry.value
+ }
+ }
+
+ /// Return the maximum number of key-value pairs the cache can hold.
+ pub fn capacity(&self) -> uint {
+ self.max_size
+ }
+
+ /// Change the number of key-value pairs the cache can hold. Remove
+ /// least-recently-used key-value pairs if necessary.
+ pub fn change_capacity(&mut self, capacity: uint) {
+ for _ in range(capacity, self.len()) {
+ self.remove_lru();
+ }
+ self.max_size = capacity;
+ }
+
+ #[inline]
+ fn remove_lru(&mut self) {
+ if self.len() > 0 {
+ let lru = unsafe { (*self.tail).prev };
+ self.detach(lru);
+ unsafe {
+ match (*lru).key {
+ None => (),
+ Some(ref k) => { self.map.pop(&KeyRef{k: k}); }
+ }
+ }
+ }
+ }
+
+ #[inline]
+ fn detach(&mut self, node: *mut LruEntry<K, V>) {
+ unsafe {
+ (*(*node).prev).next = (*node).next;
+ (*(*node).next).prev = (*node).prev;
+ }
+ }
+
+ #[inline]
+ fn attach(&mut self, node: *mut LruEntry<K, V>) {
+ unsafe {
+ (*node).next = (*self.head).next;
+ (*node).prev = self.head;
+ (*self.head).next = node;
+ (*(*node).next).prev = node;
+ }
+ }
+}
+
+impl<A: ToStr + IterBytes + Eq, B: ToStr> ToStr for LruCache<A, B> {
+ /// Return a string that lists the key-value pairs from most-recently
+ /// used to least-recently used.
+ #[inline]
+ fn to_str(&self) -> ~str {
+ let mut acc = ~"{";
+ let mut cur = self.head;
+ for i in range(0, self.len()) {
+ if i > 0 {
+ acc.push_str(", ");
+ }
+ unsafe {
+ cur = (*cur).next;
+ match (*cur).key {
+ // should never print nil
+ None => acc.push_str("nil"),
+ Some(ref k) => acc.push_str(k.to_str())
+ }
+ }
+ acc.push_str(": ");
+ unsafe {
+ match (*cur).value {
+ // should never print nil
+ None => acc.push_str("nil"),
+ Some(ref value) => acc.push_str(value.to_str())
+ }
+ }
+ }
+ acc.push_char('}');
+ acc
+ }
+}
+
+impl<K: IterBytes + Eq, V> Container for LruCache<K, V> {
+ /// Return the number of key-value pairs in the cache.
+ fn len(&self) -> uint {
+ self.map.len()
+ }
+}
+
+impl<K: IterBytes + Eq, V> Mutable for LruCache<K, V> {
+ /// Clear the cache of all key-value pairs.
+ fn clear(&mut self) {
+ self.map.clear();
+ }
+}
+
+#[unsafe_destructor]
+impl<K, V> Drop for LruCache<K, V> {
+ fn drop(&mut self) {
+ unsafe {
+ let _: ~LruEntry<K, V> = cast::transmute(self.head);
+ let _: ~LruEntry<K, V> = cast::transmute(self.tail);
+ }
+ }
+}
+
+#[cfg(test)]
+mod tests {
+ use super::LruCache;
+
+ fn assert_opt_eq<V: Eq>(opt: Option<&V>, v: V) {
+ assert!(opt.is_some());
+ assert_eq!(opt.unwrap(), &v);
+ }
+
+ #[test]
+ fn test_put_and_get() {
+ let mut cache: LruCache<int, int> = LruCache::new(2);
+ cache.put(1, 10);
+ cache.put(2, 20);
+ assert_opt_eq(cache.get(&1), 10);
+ assert_opt_eq(cache.get(&2), 20);
+ assert_eq!(cache.len(), 2);
+ }
+
+ #[test]
+ fn test_put_update() {
+ let mut cache: LruCache<~str, ~[u8]> = LruCache::new(1);
+ cache.put(~"1", ~[10, 10]);
+ cache.put(~"1", ~[10, 19]);
+ assert_opt_eq(cache.get(&~"1"), ~[10, 19]);
+ assert_eq!(cache.len(), 1);
+ }
+
+ #[test]
+ fn test_expire_lru() {
+ let mut cache: LruCache<~str, ~str> = LruCache::new(2);
+ cache.put(~"foo1", ~"bar1");
+ cache.put(~"foo2", ~"bar2");
+ cache.put(~"foo3", ~"bar3");
+ assert!(cache.get(&~"foo1").is_none());
+ cache.put(~"foo2", ~"bar2update");
+ cache.put(~"foo4", ~"bar4");
+ assert!(cache.get(&~"foo3").is_none());
+ }
+
+ #[test]
+ fn test_pop() {
+ let mut cache: LruCache<int, int> = LruCache::new(2);
+ cache.put(1, 10);
+ cache.put(2, 20);
+ assert_eq!(cache.len(), 2);
+ let opt1 = cache.pop(&1);
+ assert!(opt1.is_some());
+ assert_eq!(opt1.unwrap(), 10);
+ assert!(cache.get(&1).is_none());
+ assert_eq!(cache.len(), 1);
+ }
+
+ #[test]
+ fn test_change_capacity() {
+ let mut cache: LruCache<int, int> = LruCache::new(2);
+ assert_eq!(cache.capacity(), 2);
+ cache.put(1, 10);
+ cache.put(2, 20);
+ cache.change_capacity(1);
+ assert!(cache.get(&1).is_none());
+ assert_eq!(cache.capacity(), 1);
+ }
+
+ #[test]
+ fn test_to_str() {
+ let mut cache: LruCache<int, int> = LruCache::new(3);
+ cache.put(1, 10);
+ cache.put(2, 20);
+ cache.put(3, 30);
+ assert_eq!(cache.to_str(), ~"{3: 30, 2: 20, 1: 10}");
+ cache.put(2, 22);
+ assert_eq!(cache.to_str(), ~"{2: 22, 3: 30, 1: 10}");
+ cache.put(6, 60);
+ assert_eq!(cache.to_str(), ~"{6: 60, 2: 22, 3: 30}");
+ cache.get(&3);
+ assert_eq!(cache.to_str(), ~"{3: 30, 6: 60, 2: 22}");
+ cache.change_capacity(2);
+ assert_eq!(cache.to_str(), ~"{3: 30, 6: 60}");
+ }
+
+ #[test]
+ fn test_clear() {
+ let mut cache: LruCache<int, int> = LruCache::new(2);
+ cache.put(1, 10);
+ cache.put(2, 20);
+ cache.clear();
+ assert!(cache.get(&1).is_none());
+ assert!(cache.get(&2).is_none());
+ assert_eq!(cache.to_str(), ~"{}");
+ }
+}