OpenTTD Source: src/misc/lrucache.hpp Source File

OpenTTD Source 13.2.1

lrucache.hpp
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1 /*
2 * This file is part of OpenTTD.
3 * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
4 * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
5 * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
6 */
7
10 #ifndef LRUCACHE_HPP
11 #define LRUCACHE_HPP
12
13 #include <utility>
14 #include <list>
15 #include <functional>
16 #include <unordered_map>
17 #include <stdexcept>
18
24 template <class Tkey, class Tdata>
25 class LRUCache {
26 private:
27 typedef std::pair<Tkey, Tdata *> Tpair;
28 typedef typename std::list<Tpair>::iterator Titer;
29
30 std::list<Tpair> data;
31 std::unordered_map<Tkey, Titer> lookup;
32
33 const size_t capacity;
34
35 public:
40 LRUCache(size_t max_items) : capacity(max_items) {}
41
47 inline bool Contains(const Tkey key)
48 {
49 return this->lookup.find(key) != this->lookup.end();
50 }
51
58 Tdata *Insert(const Tkey key, Tdata *item)
59 {
60 Tdata *old = nullptr;
61
62 if (this->Contains(key)) {
63 /* Replace old value. */
64 old = this->lookup[key]->second;
65 this->lookup[key]->second = item;
66 } else {
67 /* Delete least used item if maximum items cached. */
68 if (this->data.size() >= this->capacity) {
69 Tpair last = data.back();
70 this->lookup.erase(last.first);
71 this->data.pop_back();
72
73 old = last.second;
74 }
75
76 /* Insert new item. */
77 this->data.push_front(std::make_pair(key, item));
78 this->lookup.emplace(key, this->data.begin());
79 }
80
81 return old;
82 }
83
88 inline Tdata *Pop()
89 {
90 if (this->data.empty()) return nullptr;
91
92 Tdata *value = this->data.back().second;
93 this->lookup.erase(this->data.back().first);
94 this->data.pop_back();
95 return value;
96 }
97
104 inline Tdata *Get(const Tkey key)
105 {
106 if (this->lookup.find(key) == this->lookup.end()) throw std::out_of_range("item not found");
107 /* Move to front if needed. */
108 this->data.splice(this->data.begin(), this->data, this->lookup[key]);
109
110 return this->data.front().second;
111 }
112 };
113
114 #endif /* LRUCACHE_HPP */
LRUCache::Get
Tdata * Get(const Tkey key)
Get an item from the cache.
Definition: lrucache.hpp:104
LRUCache::Pop
Tdata * Pop()
Pop the least recently used item.
Definition: lrucache.hpp:88
LRUCache
Size limited cache with a least recently used eviction strategy.
Definition: lrucache.hpp:25
LRUCache::LRUCache
LRUCache(size_t max_items)
Construct new LRU cache map.
Definition: lrucache.hpp:40
LRUCache::Contains
bool Contains(const Tkey key)
Test if a key is already contained in the cache.
Definition: lrucache.hpp:47
LRUCache::capacity
const size_t capacity
Number of items to cache.
Definition: lrucache.hpp:33
LRUCache::Insert
Tdata * Insert(const Tkey key, Tdata *item)
Insert a new data item with a specified key.
Definition: lrucache.hpp:58
LRUCache::data
std::list< Tpair > data
Ordered list of all items.
Definition: lrucache.hpp:30
LRUCache::lookup
std::unordered_map< Tkey, Titer > lookup
Map of keys to items.
Definition: lrucache.hpp:31