1 /* 2 * Copyright (c) Facebook, Inc. and its affiliates. 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 #pragma once 18 19 #include <utility> 20 21 #include <folly/Optional.h> 22 #include <folly/container/EvictingCacheMap.h> 23 #include <folly/dynamic.h> 24 #include <wangle/client/persistence/PersistentCacheCommon.h> 25 26 namespace wangle { 27 28 /** 29 * A threadsafe cache map that delegates to an EvictingCacheMap and maintains 30 * a version of the data. 31 */ 32 template <typename K, typename V, typename MutexT> 33 class LRUInMemoryCache { 34 public: 35 /** 36 * Create with the specified capacity. 37 */ LRUInMemoryCache(size_t capacity)38 explicit LRUInMemoryCache(size_t capacity) : cache_(capacity) {} 39 ~LRUInMemoryCache() = default; 40 41 folly::Optional<V> get(const K& key); 42 void put(const K& key, const V& val); 43 bool remove(const K& key); 44 size_t size() const; 45 void clear(); 46 47 CacheDataVersion getVersion() const; 48 49 /** 50 * Loads the list of kv pairs into the cache and bumps version. 51 * Returns the new cache version. 52 */ 53 CacheDataVersion loadData(const folly::dynamic& kvPairs) noexcept; 54 55 /** 56 * Get the cache data as a list of kv pairs along with the version 57 */ 58 folly::Optional<std::pair<folly::dynamic, CacheDataVersion>> 59 convertToKeyValuePairs() noexcept; 60 61 /** 62 * Determine if the cache has changed since the specified version 63 */ hasChangedSince(CacheDataVersion version)64 bool hasChangedSince(CacheDataVersion version) const { 65 return getVersion() != version; 66 } 67 68 private: 69 // must be called under a write lock incrementVersion()70 void incrementVersion() { 71 ++version_; 72 // if a uint64_t is incremented a billion times a second, it will still take 73 // 585 years to wrap around, so don't bother 74 } 75 76 folly::EvictingCacheMap<K, V> cache_; 77 // Version always starts at 1 78 CacheDataVersion version_{kDefaultInitCacheDataVersion}; 79 // mutable so we can take read locks in const methods 80 mutable MutexT cacheLock_; 81 }; 82 83 } // namespace wangle 84 85 #include <wangle/client/persistence/LRUInMemoryCache-inl.h> 86