| // Copyright 2020 The SwiftShader Authors. All Rights Reserved. |
| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); |
| // you may not use this file except in compliance with the License. |
| // You may obtain a copy of the License at |
| // |
| // http://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| // See the License for the specific language governing permissions and |
| // limitations under the License. |
| |
| #ifndef sw_LRUCache_hpp |
| #define sw_LRUCache_hpp |
| |
| #include "System/Debug.hpp" |
| |
| #include <cstddef> |
| #include <functional> |
| #include <unordered_set> |
| #include <vector> |
| |
| namespace sw { |
| |
| // LRUCache is a least recently used cache of a fixed capacity. |
| template<typename KEY, typename DATA, typename HASH = std::hash<KEY> > |
| class LRUCache |
| { |
| struct Entry; |
| |
| public: |
| using Key = KEY; |
| using Data = DATA; |
| using Hash = HASH; |
| |
| // view is a const accessor of a single cache entry. |
| class view |
| { |
| public: |
| inline view(Entry *); |
| |
| inline const Key &key() const; |
| inline const Data &data() const; |
| |
| private: |
| Entry *entry; |
| }; |
| |
| class iterator |
| { |
| public: |
| inline iterator(Entry *); |
| inline view operator*() const; |
| inline iterator &operator++(); |
| inline bool operator==(const iterator &) const; |
| inline bool operator!=(const iterator &) const; |
| |
| private: |
| Entry *entry; |
| }; |
| |
| // Construct a LRU cache with the given maximum number of entries. |
| inline LRUCache(size_t capacity); |
| inline ~LRUCache() = default; |
| |
| // lookup() looks up the cache entry with the given key. |
| // If the entry is found, this is moved to the most-recent position in the |
| // cache, and its data is returned. |
| // If the entry is not found, then a default initialized Data is returned. |
| inline Data lookup(const Key &key); |
| |
| // add() adds the data to the cache using the given key, placed at the |
| // most-recent position in the cache. |
| // If an existing entry exists in the cache with the given key, then this is |
| // replaced with data. |
| // If no existing entry exists in the cache, and the cache is already full |
| // then the least recently used entry is evicted before adding the new |
| // entry. |
| inline void add(const Key &key, const Data &data); |
| |
| // clear() clears the cache of all elements. |
| inline void clear(); |
| |
| // Range based iterators. |
| inline iterator begin() const; |
| inline iterator end() const; |
| |
| private: |
| LRUCache(const LRUCache &) = delete; |
| LRUCache(LRUCache &&) = delete; |
| LRUCache &operator=(const LRUCache &) = delete; |
| LRUCache &operator=(LRUCache &&) = delete; |
| |
| // Keyed holds a key. See find() for more information. |
| struct Keyed |
| { |
| Key key = {}; |
| }; |
| |
| // Cache entry structure. |
| // Holds the unique copy of the key and data, along with pointers for |
| // maintaining the linked list. |
| struct Entry : Keyed |
| { |
| Data data = {}; |
| Entry *next = nullptr; |
| Entry *prev = nullptr; |
| }; |
| |
| // KeyedComparator is a custom hasher and equality helper for Keyed. |
| struct KeyedComparator |
| { |
| // Hash function. |
| inline uint64_t operator()(const Keyed *k) const; |
| |
| // Equality function. |
| inline uint64_t operator()(const Keyed *a, const Keyed *b) const; |
| }; |
| |
| // find() returns the Entry* for the given key, or nullptr. |
| // find() performs this by casting the Key pointer to a Keyed pointer for |
| // searching the std::unordered_set. |
| // |
| // This is to avoid having a duplicate Key held by both an |
| // unordered_map<Key, Entry*> and the Entry itself, as the Key type may be |
| // large. |
| // |
| // While we could use an unordered_set<Entry*>, this then requires the |
| // construction of a temporary Entry to perform the call to |
| // unordered_set<Entry*>::find(). This is undesirable as the Data type might |
| // be large or have an expensive constructor. |
| // |
| // C++20 gains a new templated overload for unordered_set<Entry*>::find() |
| // which would allow us to use unordered_set<Entry*>::find(Key*). |
| // Until we can use C++20, keep this casting nastiness hidden away in this |
| // one function. |
| inline Entry *find(const Key &key); |
| |
| // unlinks the entry from the list it is linked in. |
| inline void unlink(Entry *); |
| |
| // links the entry to the head of the LRU. |
| inline void link(Entry *); |
| |
| // storage holds the allocations of all the entries. |
| // This vector must not change size for the lifetime of the cache. |
| std::vector<Entry> storage; |
| |
| // set is an unordered set of Keyed*, using the KeyedComparator for hash and |
| // equality testing. |
| std::unordered_set<const Keyed *, KeyedComparator, KeyedComparator> set; |
| |
| Entry *free = nullptr; // Singly-linked (prev is nullptr) list of free entries. |
| Entry *head = nullptr; // Pointer to the most recently used entry in the LRU. |
| Entry *tail = nullptr; // Pointer to the least recently used entry in the LRU. |
| }; |
| |
| //////////////////////////////////////////////////////////////////////////////// |
| // LRUCache<>::view |
| //////////////////////////////////////////////////////////////////////////////// |
| template<typename KEY, typename DATA, typename HASH> |
| LRUCache<KEY, DATA, HASH>::view::view(Entry *entry) |
| : entry(entry) |
| {} |
| |
| template<typename KEY, typename DATA, typename HASH> |
| const KEY &LRUCache<KEY, DATA, HASH>::view::key() const |
| { |
| return entry->key; |
| } |
| |
| template<typename KEY, typename DATA, typename HASH> |
| const DATA &LRUCache<KEY, DATA, HASH>::view::data() const |
| { |
| return entry->data; |
| } |
| |
| //////////////////////////////////////////////////////////////////////////////// |
| // LRUCache<>::iterator |
| //////////////////////////////////////////////////////////////////////////////// |
| template<typename KEY, typename DATA, typename HASH> |
| LRUCache<KEY, DATA, HASH>::iterator::iterator(Entry *entry) |
| : entry(entry) |
| {} |
| |
| template<typename KEY, typename DATA, typename HASH> |
| typename LRUCache<KEY, DATA, HASH>::view LRUCache<KEY, DATA, HASH>::iterator::operator*() const |
| { |
| return view{ entry }; |
| } |
| |
| template<typename KEY, typename DATA, typename HASH> |
| typename LRUCache<KEY, DATA, HASH>::iterator &LRUCache<KEY, DATA, HASH>::iterator::operator++() |
| { |
| entry = entry->next; |
| return *this; |
| } |
| |
| template<typename KEY, typename DATA, typename HASH> |
| bool LRUCache<KEY, DATA, HASH>::iterator::operator==(const iterator &rhs) const |
| { |
| return entry == rhs.entry; |
| } |
| |
| template<typename KEY, typename DATA, typename HASH> |
| bool LRUCache<KEY, DATA, HASH>::iterator::operator!=(const iterator &rhs) const |
| { |
| return entry != rhs.entry; |
| } |
| |
| //////////////////////////////////////////////////////////////////////////////// |
| // LRUCache<> |
| //////////////////////////////////////////////////////////////////////////////// |
| template<typename KEY, typename DATA, typename HASH> |
| LRUCache<KEY, DATA, HASH>::LRUCache(size_t capacity) |
| : storage(capacity) |
| { |
| for(size_t i = 0; i < capacity; i++) |
| { |
| Entry *entry = &storage[i]; |
| entry->next = free; // No need for back link here. |
| free = entry; |
| } |
| } |
| |
| template<typename KEY, typename DATA, typename HASH> |
| DATA LRUCache<KEY, DATA, HASH>::lookup(const Key &key) |
| { |
| if(Entry *entry = find(key)) |
| { |
| unlink(entry); |
| link(entry); |
| return entry->data; |
| } |
| return {}; |
| } |
| |
| template<typename KEY, typename DATA, typename HASH> |
| void LRUCache<KEY, DATA, HASH>::add(const Key &key, const Data &data) |
| { |
| if(Entry *entry = find(key)) |
| { |
| // Move entry to front. |
| unlink(entry); |
| link(entry); |
| entry->data = data; |
| return; |
| } |
| |
| Entry *entry = free; |
| if(entry) |
| { |
| // Unlink from free. |
| free = entry->next; |
| entry->next = nullptr; |
| } |
| else |
| { |
| // Unlink least recently used. |
| entry = tail; |
| unlink(entry); |
| set.erase(entry); |
| } |
| |
| // link as most recently used. |
| link(entry); |
| if(tail == nullptr) |
| { |
| tail = entry; |
| } |
| |
| entry->key = key; |
| entry->data = data; |
| set.emplace(entry); |
| } |
| |
| template<typename KEY, typename DATA, typename HASH> |
| void LRUCache<KEY, DATA, HASH>::clear() |
| { |
| while(Entry *entry = head) |
| { |
| unlink(entry); |
| entry->next = free; // No need for back link here. |
| free = entry; |
| } |
| set.clear(); |
| } |
| |
| template<typename KEY, typename DATA, typename HASH> |
| typename LRUCache<KEY, DATA, HASH>::iterator LRUCache<KEY, DATA, HASH>::begin() const |
| { |
| return { head }; |
| } |
| |
| template<typename KEY, typename DATA, typename HASH> |
| typename LRUCache<KEY, DATA, HASH>::iterator LRUCache<KEY, DATA, HASH>::end() const |
| { |
| return { nullptr }; |
| } |
| |
| template<typename KEY, typename DATA, typename HASH> |
| void LRUCache<KEY, DATA, HASH>::unlink(Entry *entry) |
| { |
| if(head == entry) { head = entry->next; } |
| if(tail == entry) { tail = entry->prev; } |
| if(entry->prev) { entry->prev->next = entry->next; } |
| if(entry->next) { entry->next->prev = entry->prev; } |
| entry->prev = nullptr; |
| entry->next = nullptr; |
| } |
| |
| template<typename KEY, typename DATA, typename HASH> |
| void LRUCache<KEY, DATA, HASH>::link(Entry *entry) |
| { |
| ASSERT_MSG(entry->next == nullptr, "link() called on entry already linked"); |
| ASSERT_MSG(entry->prev == nullptr, "link() called on entry already linked"); |
| if(head) |
| { |
| entry->next = head; |
| head->prev = entry; |
| } |
| head = entry; |
| if(!tail) { tail = entry; } |
| } |
| |
| template<typename KEY, typename DATA, typename HASH> |
| typename LRUCache<KEY, DATA, HASH>::Entry *LRUCache<KEY, DATA, HASH>::find(const Key &key) |
| { |
| auto asKeyed = reinterpret_cast<const Keyed *>(&key); |
| auto it = set.find(asKeyed); |
| if(it == set.end()) |
| { |
| return nullptr; |
| } |
| return const_cast<Entry *>(static_cast<const Entry *>(*it)); |
| } |
| |
| //////////////////////////////////////////////////////////////////////////////// |
| // LRUCache<>::KeyedComparator |
| //////////////////////////////////////////////////////////////////////////////// |
| template<typename KEY, typename DATA, typename HASH> |
| uint64_t LRUCache<KEY, DATA, HASH>::KeyedComparator::operator()(const Keyed *k) const |
| { |
| return Hash()(k->key); |
| } |
| |
| template<typename KEY, typename DATA, typename HASH> |
| uint64_t LRUCache<KEY, DATA, HASH>::KeyedComparator::operator()(const Keyed *a, const Keyed *b) const |
| { |
| return a->key == b->key; |
| } |
| |
| } // namespace sw |
| |
| #endif // sw_LRUCache_hpp |