From 5e650d6d2dbfc284c300668e71188e663d8f0a45 Mon Sep 17 00:00:00 2001 From: Mike Hearn Date: Mon, 25 Jun 2012 11:17:22 +0200 Subject: Import LevelDB 1.5, it will be used for the transaction database. --- src/leveldb/util/cache.cc | 328 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 328 insertions(+) create mode 100644 src/leveldb/util/cache.cc (limited to 'src/leveldb/util/cache.cc') diff --git a/src/leveldb/util/cache.cc b/src/leveldb/util/cache.cc new file mode 100644 index 0000000000..24f1f63f4f --- /dev/null +++ b/src/leveldb/util/cache.cc @@ -0,0 +1,328 @@ +// Copyright (c) 2011 The LevelDB Authors. All rights reserved. +// Use of this source code is governed by a BSD-style license that can be +// found in the LICENSE file. See the AUTHORS file for names of contributors. + +#include +#include +#include + +#include "leveldb/cache.h" +#include "port/port.h" +#include "util/hash.h" +#include "util/mutexlock.h" + +namespace leveldb { + +Cache::~Cache() { +} + +namespace { + +// LRU cache implementation + +// An entry is a variable length heap-allocated structure. Entries +// are kept in a circular doubly linked list ordered by access time. +struct LRUHandle { + void* value; + void (*deleter)(const Slice&, void* value); + LRUHandle* next_hash; + LRUHandle* next; + LRUHandle* prev; + size_t charge; // TODO(opt): Only allow uint32_t? + size_t key_length; + uint32_t refs; + uint32_t hash; // Hash of key(); used for fast sharding and comparisons + char key_data[1]; // Beginning of key + + Slice key() const { + // For cheaper lookups, we allow a temporary Handle object + // to store a pointer to a key in "value". + if (next == this) { + return *(reinterpret_cast(value)); + } else { + return Slice(key_data, key_length); + } + } +}; + +// We provide our own simple hash table since it removes a whole bunch +// of porting hacks and is also faster than some of the built-in hash +// table implementations in some of the compiler/runtime combinations +// we have tested. E.g., readrandom speeds up by ~5% over the g++ +// 4.4.3's builtin hashtable. +class HandleTable { + public: + HandleTable() : length_(0), elems_(0), list_(NULL) { Resize(); } + ~HandleTable() { delete[] list_; } + + LRUHandle* Lookup(const Slice& key, uint32_t hash) { + return *FindPointer(key, hash); + } + + LRUHandle* Insert(LRUHandle* h) { + LRUHandle** ptr = FindPointer(h->key(), h->hash); + LRUHandle* old = *ptr; + h->next_hash = (old == NULL ? NULL : old->next_hash); + *ptr = h; + if (old == NULL) { + ++elems_; + if (elems_ > length_) { + // Since each cache entry is fairly large, we aim for a small + // average linked list length (<= 1). + Resize(); + } + } + return old; + } + + LRUHandle* Remove(const Slice& key, uint32_t hash) { + LRUHandle** ptr = FindPointer(key, hash); + LRUHandle* result = *ptr; + if (result != NULL) { + *ptr = result->next_hash; + --elems_; + } + return result; + } + + private: + // The table consists of an array of buckets where each bucket is + // a linked list of cache entries that hash into the bucket. + uint32_t length_; + uint32_t elems_; + LRUHandle** list_; + + // Return a pointer to slot that points to a cache entry that + // matches key/hash. If there is no such cache entry, return a + // pointer to the trailing slot in the corresponding linked list. + LRUHandle** FindPointer(const Slice& key, uint32_t hash) { + LRUHandle** ptr = &list_[hash & (length_ - 1)]; + while (*ptr != NULL && + ((*ptr)->hash != hash || key != (*ptr)->key())) { + ptr = &(*ptr)->next_hash; + } + return ptr; + } + + void Resize() { + uint32_t new_length = 4; + while (new_length < elems_) { + new_length *= 2; + } + LRUHandle** new_list = new LRUHandle*[new_length]; + memset(new_list, 0, sizeof(new_list[0]) * new_length); + uint32_t count = 0; + for (uint32_t i = 0; i < length_; i++) { + LRUHandle* h = list_[i]; + while (h != NULL) { + LRUHandle* next = h->next_hash; + Slice key = h->key(); + uint32_t hash = h->hash; + LRUHandle** ptr = &new_list[hash & (new_length - 1)]; + h->next_hash = *ptr; + *ptr = h; + h = next; + count++; + } + } + assert(elems_ == count); + delete[] list_; + list_ = new_list; + length_ = new_length; + } +}; + +// A single shard of sharded cache. +class LRUCache { + public: + LRUCache(); + ~LRUCache(); + + // Separate from constructor so caller can easily make an array of LRUCache + void SetCapacity(size_t capacity) { capacity_ = capacity; } + + // Like Cache methods, but with an extra "hash" parameter. + Cache::Handle* Insert(const Slice& key, uint32_t hash, + void* value, size_t charge, + void (*deleter)(const Slice& key, void* value)); + Cache::Handle* Lookup(const Slice& key, uint32_t hash); + void Release(Cache::Handle* handle); + void Erase(const Slice& key, uint32_t hash); + + private: + void LRU_Remove(LRUHandle* e); + void LRU_Append(LRUHandle* e); + void Unref(LRUHandle* e); + + // Initialized before use. + size_t capacity_; + + // mutex_ protects the following state. + port::Mutex mutex_; + size_t usage_; + uint64_t last_id_; + + // Dummy head of LRU list. + // lru.prev is newest entry, lru.next is oldest entry. + LRUHandle lru_; + + HandleTable table_; +}; + +LRUCache::LRUCache() + : usage_(0), + last_id_(0) { + // Make empty circular linked list + lru_.next = &lru_; + lru_.prev = &lru_; +} + +LRUCache::~LRUCache() { + for (LRUHandle* e = lru_.next; e != &lru_; ) { + LRUHandle* next = e->next; + assert(e->refs == 1); // Error if caller has an unreleased handle + Unref(e); + e = next; + } +} + +void LRUCache::Unref(LRUHandle* e) { + assert(e->refs > 0); + e->refs--; + if (e->refs <= 0) { + usage_ -= e->charge; + (*e->deleter)(e->key(), e->value); + free(e); + } +} + +void LRUCache::LRU_Remove(LRUHandle* e) { + e->next->prev = e->prev; + e->prev->next = e->next; +} + +void LRUCache::LRU_Append(LRUHandle* e) { + // Make "e" newest entry by inserting just before lru_ + e->next = &lru_; + e->prev = lru_.prev; + e->prev->next = e; + e->next->prev = e; +} + +Cache::Handle* LRUCache::Lookup(const Slice& key, uint32_t hash) { + MutexLock l(&mutex_); + LRUHandle* e = table_.Lookup(key, hash); + if (e != NULL) { + e->refs++; + LRU_Remove(e); + LRU_Append(e); + } + return reinterpret_cast(e); +} + +void LRUCache::Release(Cache::Handle* handle) { + MutexLock l(&mutex_); + Unref(reinterpret_cast(handle)); +} + +Cache::Handle* LRUCache::Insert( + const Slice& key, uint32_t hash, void* value, size_t charge, + void (*deleter)(const Slice& key, void* value)) { + MutexLock l(&mutex_); + + LRUHandle* e = reinterpret_cast( + malloc(sizeof(LRUHandle)-1 + key.size())); + e->value = value; + e->deleter = deleter; + e->charge = charge; + e->key_length = key.size(); + e->hash = hash; + e->refs = 2; // One from LRUCache, one for the returned handle + memcpy(e->key_data, key.data(), key.size()); + LRU_Append(e); + usage_ += charge; + + LRUHandle* old = table_.Insert(e); + if (old != NULL) { + LRU_Remove(old); + Unref(old); + } + + while (usage_ > capacity_ && lru_.next != &lru_) { + LRUHandle* old = lru_.next; + LRU_Remove(old); + table_.Remove(old->key(), old->hash); + Unref(old); + } + + return reinterpret_cast(e); +} + +void LRUCache::Erase(const Slice& key, uint32_t hash) { + MutexLock l(&mutex_); + LRUHandle* e = table_.Remove(key, hash); + if (e != NULL) { + LRU_Remove(e); + Unref(e); + } +} + +static const int kNumShardBits = 4; +static const int kNumShards = 1 << kNumShardBits; + +class ShardedLRUCache : public Cache { + private: + LRUCache shard_[kNumShards]; + port::Mutex id_mutex_; + uint64_t last_id_; + + static inline uint32_t HashSlice(const Slice& s) { + return Hash(s.data(), s.size(), 0); + } + + static uint32_t Shard(uint32_t hash) { + return hash >> (32 - kNumShardBits); + } + + public: + explicit ShardedLRUCache(size_t capacity) + : last_id_(0) { + const size_t per_shard = (capacity + (kNumShards - 1)) / kNumShards; + for (int s = 0; s < kNumShards; s++) { + shard_[s].SetCapacity(per_shard); + } + } + virtual ~ShardedLRUCache() { } + virtual Handle* Insert(const Slice& key, void* value, size_t charge, + void (*deleter)(const Slice& key, void* value)) { + const uint32_t hash = HashSlice(key); + return shard_[Shard(hash)].Insert(key, hash, value, charge, deleter); + } + virtual Handle* Lookup(const Slice& key) { + const uint32_t hash = HashSlice(key); + return shard_[Shard(hash)].Lookup(key, hash); + } + virtual void Release(Handle* handle) { + LRUHandle* h = reinterpret_cast(handle); + shard_[Shard(h->hash)].Release(handle); + } + virtual void Erase(const Slice& key) { + const uint32_t hash = HashSlice(key); + shard_[Shard(hash)].Erase(key, hash); + } + virtual void* Value(Handle* handle) { + return reinterpret_cast(handle)->value; + } + virtual uint64_t NewId() { + MutexLock l(&id_mutex_); + return ++(last_id_); + } +}; + +} // end anonymous namespace + +Cache* NewLRUCache(size_t capacity) { + return new ShardedLRUCache(capacity); +} + +} // namespace leveldb -- cgit v1.2.3