added limit to cached username colors (#2515)

lib/lrucache/lrucache/lrucache.hpp

@@ -0,0 +1,72 @@
+/* 
+ * File:   lrucache.hpp
+ * Author: Alexander Ponomarev
+ *
+ * Created on June 20, 2013, 5:09 PM
+ */
+
+#ifndef _LRUCACHE_HPP_INCLUDED_
+#define	_LRUCACHE_HPP_INCLUDED_
+
+#include <unordered_map>
+#include <list>
+#include <cstddef>
+#include <stdexcept>
+
+namespace cache {
+
+template<typename key_t, typename value_t>
+class lru_cache {
+public:
+	typedef typename std::pair<key_t, value_t> key_value_pair_t;
+	typedef typename std::list<key_value_pair_t>::iterator list_iterator_t;
+
+	lru_cache(size_t max_size) :
+		_max_size(max_size) {
+	}
+	
+	void put(const key_t& key, const value_t& value) {
+		auto it = _cache_items_map.find(key);
+		_cache_items_list.push_front(key_value_pair_t(key, value));
+		if (it != _cache_items_map.end()) {
+			_cache_items_list.erase(it->second);
+			_cache_items_map.erase(it);
+		}
+		_cache_items_map[key] = _cache_items_list.begin();
+		
+		if (_cache_items_map.size() > _max_size) {
+			auto last = _cache_items_list.end();
+			last--;
+			_cache_items_map.erase(last->first);
+			_cache_items_list.pop_back();
+		}
+	}
+	
+	const value_t& get(const key_t& key) {
+		auto it = _cache_items_map.find(key);
+		if (it == _cache_items_map.end()) {
+			throw std::range_error("There is no such key in cache");
+		} else {
+			_cache_items_list.splice(_cache_items_list.begin(), _cache_items_list, it->second);
+			return it->second->second;
+		}
+	}
+	
+	bool exists(const key_t& key) const {
+		return _cache_items_map.find(key) != _cache_items_map.end();
+	}
+	
+	size_t size() const {
+		return _cache_items_map.size();
+	}
+	
+private:
+	std::list<key_value_pair_t> _cache_items_list;
+	std::unordered_map<key_t, list_iterator_t> _cache_items_map;
+	size_t _max_size;
+};
+
+} // namespace cache
+
+#endif	/* _LRUCACHE_HPP_INCLUDED_ */
+