Summary: ... so that I can include the header and create LRUCache specific tests for D61977 Test Plan: make check Reviewers: lightmark, IslamAbdelRahman, sdong Reviewed By: sdong Subscribers: andrewkr, dhruba, leveldb Differential Revision: https://reviews.facebook.net/D62145main
Yi Wu
8 years ago
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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under the BSD-style license found in the
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// LICENSE file in the root directory of this source tree. An additional grant
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// of patent rights can be found in the PATENTS file in the same directory.
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//
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// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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#pragma once |
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#include "util/sharded_cache.h" |
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#include "port/port.h" |
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#include "util/autovector.h" |
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namespace rocksdb { |
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// LRU cache implementation
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// An entry is a variable length heap-allocated structure.
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// Entries are referenced by cache and/or by any external entity.
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// The cache keeps all its entries in table. Some elements
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// are also stored on LRU list.
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//
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// LRUHandle can be in these states:
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// 1. Referenced externally AND in hash table.
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// In that case the entry is *not* in the LRU. (refs > 1 && in_cache == true)
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// 2. Not referenced externally and in hash table. In that case the entry is
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// in the LRU and can be freed. (refs == 1 && in_cache == true)
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// 3. Referenced externally and not in hash table. In that case the entry is
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// in not on LRU and not in table. (refs >= 1 && in_cache == false)
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//
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// All newly created LRUHandles are in state 1. If you call
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// LRUCacheShard::Release
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// on entry in state 1, it will go into state 2. To move from state 1 to
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// state 3, either call LRUCacheShard::Erase or LRUCacheShard::Insert with the
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// same key.
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// To move from state 2 to state 1, use LRUCacheShard::Lookup.
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// Before destruction, make sure that no handles are in state 1. This means
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// that any successful LRUCacheShard::Lookup/LRUCacheShard::Insert have a
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// matching
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// RUCache::Release (to move into state 2) or LRUCacheShard::Erase (for state 3)
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struct LRUHandle { |
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void* value; |
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void (*deleter)(const Slice&, void* value); |
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LRUHandle* next_hash; |
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LRUHandle* next; |
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LRUHandle* prev; |
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size_t charge; // TODO(opt): Only allow uint32_t?
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size_t key_length; |
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uint32_t refs; // a number of refs to this entry
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// cache itself is counted as 1
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bool in_cache; // true, if this entry is referenced by the hash table
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uint32_t hash; // Hash of key(); used for fast sharding and comparisons
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char key_data[1]; // Beginning of key
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Slice key() const { |
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// For cheaper lookups, we allow a temporary Handle object
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// to store a pointer to a key in "value".
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if (next == this) { |
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return *(reinterpret_cast<Slice*>(value)); |
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} else { |
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return Slice(key_data, key_length); |
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} |
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} |
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void Free() { |
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assert((refs == 1 && in_cache) || (refs == 0 && !in_cache)); |
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(*deleter)(key(), value); |
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delete[] reinterpret_cast<char*>(this); |
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} |
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}; |
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// We provide our own simple hash table since it removes a whole bunch
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// of porting hacks and is also faster than some of the built-in hash
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// table implementations in some of the compiler/runtime combinations
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// we have tested. E.g., readrandom speeds up by ~5% over the g++
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// 4.4.3's builtin hashtable.
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class LRUHandleTable { |
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public: |
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LRUHandleTable(); |
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~LRUHandleTable(); |
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LRUHandle* Lookup(const Slice& key, uint32_t hash); |
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LRUHandle* Insert(LRUHandle* h); |
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LRUHandle* Remove(const Slice& key, uint32_t hash); |
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template <typename T> |
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void ApplyToAllCacheEntries(T func) { |
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for (uint32_t i = 0; i < length_; i++) { |
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LRUHandle* h = list_[i]; |
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while (h != nullptr) { |
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auto n = h->next_hash; |
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assert(h->in_cache); |
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func(h); |
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h = n; |
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} |
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} |
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} |
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private: |
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// Return a pointer to slot that points to a cache entry that
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// matches key/hash. If there is no such cache entry, return a
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// pointer to the trailing slot in the corresponding linked list.
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LRUHandle** FindPointer(const Slice& key, uint32_t hash); |
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void Resize(); |
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// The table consists of an array of buckets where each bucket is
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// a linked list of cache entries that hash into the bucket.
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uint32_t length_; |
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uint32_t elems_; |
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LRUHandle** list_; |
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}; |
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// A single shard of sharded cache.
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class LRUCacheShard : public CacheShard { |
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public: |
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LRUCacheShard(); |
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virtual ~LRUCacheShard(); |
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// Separate from constructor so caller can easily make an array of LRUCache
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// if current usage is more than new capacity, the function will attempt to
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// free the needed space
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virtual void SetCapacity(size_t capacity) override; |
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// Set the flag to reject insertion if cache if full.
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virtual void SetStrictCapacityLimit(bool strict_capacity_limit) override; |
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// Like Cache methods, but with an extra "hash" parameter.
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virtual Status Insert(const Slice& key, uint32_t hash, void* value, |
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size_t charge, |
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void (*deleter)(const Slice& key, void* value), |
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Cache::Handle** handle) override; |
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virtual Cache::Handle* Lookup(const Slice& key, uint32_t hash) override; |
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virtual void Release(Cache::Handle* handle) override; |
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virtual void Erase(const Slice& key, uint32_t hash) override; |
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// Although in some platforms the update of size_t is atomic, to make sure
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// GetUsage() and GetPinnedUsage() work correctly under any platform, we'll
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// protect them with mutex_.
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virtual size_t GetUsage() const override; |
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virtual size_t GetPinnedUsage() const override; |
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virtual void ApplyToAllCacheEntries(void (*callback)(void*, size_t), |
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bool thread_safe) override; |
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virtual void EraseUnRefEntries() override; |
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private: |
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void LRU_Remove(LRUHandle* e); |
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void LRU_Append(LRUHandle* e); |
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// Just reduce the reference count by 1.
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// Return true if last reference
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bool Unref(LRUHandle* e); |
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// Free some space following strict LRU policy until enough space
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// to hold (usage_ + charge) is freed or the lru list is empty
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// This function is not thread safe - it needs to be executed while
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// holding the mutex_
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void EvictFromLRU(size_t charge, autovector<LRUHandle*>* deleted); |
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// Initialized before use.
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size_t capacity_; |
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// Memory size for entries residing in the cache
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size_t usage_; |
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// Memory size for entries residing only in the LRU list
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size_t lru_usage_; |
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// Whether to reject insertion if cache reaches its full capacity.
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bool strict_capacity_limit_; |
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// mutex_ protects the following state.
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// We don't count mutex_ as the cache's internal state so semantically we
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// don't mind mutex_ invoking the non-const actions.
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mutable port::Mutex mutex_; |
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// Dummy head of LRU list.
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// lru.prev is newest entry, lru.next is oldest entry.
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// LRU contains items which can be evicted, ie reference only by cache
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LRUHandle lru_; |
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LRUHandleTable table_; |
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}; |
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} // namespace rocksdb
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