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-rw-r--r--src/leveldb/util/cache.cc328
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diff --git a/src/leveldb/util/cache.cc b/src/leveldb/util/cache.cc
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-// 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 <assert.h>
-#include <stdio.h>
-#include <stdlib.h>
-
-#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<Slice*>(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<Cache::Handle*>(e);
-}
-
-void LRUCache::Release(Cache::Handle* handle) {
- MutexLock l(&mutex_);
- Unref(reinterpret_cast<LRUHandle*>(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<LRUHandle*>(
- 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<Cache::Handle*>(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<LRUHandle*>(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<LRUHandle*>(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
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