1/*
2 * Copyright 2016 Google Inc.
3 *
4 * Use of this source code is governed by a BSD-style license that can be
5 * found in the LICENSE file.
6 */
7
8#ifndef SkLRUCache_DEFINED
9#define SkLRUCache_DEFINED
10
11#include "include/private/SkChecksum.h"
12#include "include/private/SkTHash.h"
13#include "src/core/SkTInternalLList.h"
14
15/**
16 * A generic LRU cache.
17 */
18template <typename K, typename V, typename HashK = SkGoodHash>
19class SkLRUCache : public SkNoncopyable {
20private:
21 struct Entry {
22 Entry(const K& key, V&& value)
23 : fKey(key)
24 , fValue(std::move(value)) {}
25
26 K fKey;
27 V fValue;
28
29 SK_DECLARE_INTERNAL_LLIST_INTERFACE(Entry);
30 };
31
32public:
33 explicit SkLRUCache(int maxCount)
34 : fMaxCount(maxCount) {}
35
36 ~SkLRUCache() {
37 Entry* node = fLRU.head();
38 while (node) {
39 fLRU.remove(node);
40 delete node;
41 node = fLRU.head();
42 }
43 }
44
45 V* find(const K& key) {
46 Entry** value = fMap.find(key);
47 if (!value) {
48 return nullptr;
49 }
50 Entry* entry = *value;
51 if (entry != fLRU.head()) {
52 fLRU.remove(entry);
53 fLRU.addToHead(entry);
54 } // else it's already at head position, don't need to do anything
55 return &entry->fValue;
56 }
57
58 V* insert(const K& key, V value) {
59 Entry* entry = new Entry(key, std::move(value));
60 fMap.set(entry);
61 fLRU.addToHead(entry);
62 while (fMap.count() > fMaxCount) {
63 this->remove(fLRU.tail()->fKey);
64 }
65 return &entry->fValue;
66 }
67
68 int count() {
69 return fMap.count();
70 }
71
72 template <typename Fn> // f(K*, V*)
73 void foreach(Fn&& fn) {
74 typename SkTInternalLList<Entry>::Iter iter;
75 for (Entry* e = iter.init(fLRU, SkTInternalLList<Entry>::Iter::kHead_IterStart); e;
76 e = iter.next()) {
77 fn(&e->fKey, &e->fValue);
78 }
79 }
80
81 void reset() {
82 fMap.reset();
83 for (Entry* e = fLRU.head(); e; e = fLRU.head()) {
84 fLRU.remove(e);
85 delete e;
86 }
87 }
88
89private:
90 struct Traits {
91 static const K& GetKey(Entry* e) {
92 return e->fKey;
93 }
94
95 static uint32_t Hash(const K& k) {
96 return HashK()(k);
97 }
98 };
99
100 void remove(const K& key) {
101 Entry** value = fMap.find(key);
102 SkASSERT(value);
103 Entry* entry = *value;
104 SkASSERT(key == entry->fKey);
105 fMap.remove(key);
106 fLRU.remove(entry);
107 delete entry;
108 }
109
110 int fMaxCount;
111 SkTHashTable<Entry*, K, Traits> fMap;
112 SkTInternalLList<Entry> fLRU;
113};
114
115#endif
116