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253 líneas
6.5 KiB
253 líneas
6.5 KiB
// 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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#if defined(LEVELDB_PLATFORM_POSIX) || defined(LEVELDB_PLATFORM_ANDROID)
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#include <unordered_set>
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#elif defined(LEVELDB_PLATFORM_CHROMIUM)
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#include "base/hash_tables.h"
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#else
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#include <hash_set> // TODO(sanjay): Switch to unordered_set when possible.
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#endif
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#include <assert.h>
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#include "leveldb/cache.h"
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#include "port/port.h"
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#include "util/hash.h"
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#include "util/mutexlock.h"
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namespace leveldb {
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Cache::~Cache() {
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}
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namespace {
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// LRU cache implementation
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// An entry is a variable length heap-allocated structure. Entries
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// are kept in a circular doubly linked list ordered by access time.
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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;
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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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size_t refs; // TODO(opt): Pack with "key_length"?
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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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};
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// Pick a platform specific hash_set instantiation
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#if defined(LEVELDB_PLATFORM_CHROMIUM) && defined(OS_WIN)
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// Microsoft's hash_set deviates from the standard. See
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// http://msdn.microsoft.com/en-us/library/1t4xas78(v=vs.80).aspx
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// for details. Basically the 2 param () operator is a less than and
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// the 1 param () operator is a hash function.
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struct HandleHashCompare : public stdext::hash_compare<LRUHandle*> {
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size_t operator() (LRUHandle* h) const {
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Slice k = h->key();
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return Hash(k.data(), k.size(), 0);
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}
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bool operator() (LRUHandle* a, LRUHandle* b) const {
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return a->key().compare(b->key()) < 0;
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}
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};
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typedef base::hash_set<LRUHandle*, HandleHashCompare> HandleTable;
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#else
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struct HandleHash {
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inline size_t operator()(LRUHandle* h) const {
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Slice k = h->key();
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return Hash(k.data(), k.size(), 0);
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}
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};
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struct HandleEq {
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inline bool operator()(LRUHandle* a, LRUHandle* b) const {
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return a->key() == b->key();
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}
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};
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# if defined(LEVELDB_PLATFORM_CHROMIUM)
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typedef base::hash_set<LRUHandle*, HandleHash, HandleEq> HandleTable;
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# elif defined(LEVELDB_PLATFORM_POSIX) || defined(LEVELDB_PLATFORM_ANDROID)
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typedef std::unordered_set<LRUHandle*, HandleHash, HandleEq> HandleTable;
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# else
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typedef __gnu_cxx::hash_set<LRUHandle*, HandleHash, HandleEq> HandleTable;
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# endif
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#endif
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class LRUCache : public Cache {
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public:
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explicit LRUCache(size_t capacity);
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virtual ~LRUCache();
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virtual Handle* Insert(const Slice& key, void* value, size_t charge,
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void (*deleter)(const Slice& key, void* value));
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virtual Handle* Lookup(const Slice& key);
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virtual void Release(Handle* handle);
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virtual void* Value(Handle* handle);
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virtual void Erase(const Slice& key);
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virtual uint64_t NewId();
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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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void Unref(LRUHandle* e);
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// Constructor parameters
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const size_t capacity_;
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// mutex_ protects the following state.
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port::Mutex mutex_;
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size_t usage_;
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uint64_t last_id_;
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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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LRUHandle lru_;
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HandleTable table_;
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};
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LRUCache::LRUCache(size_t capacity)
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: capacity_(capacity),
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usage_(0),
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last_id_(0) {
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// Make empty circular linked list
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lru_.next = &lru_;
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lru_.prev = &lru_;
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}
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LRUCache::~LRUCache() {
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table_.clear();
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for (LRUHandle* e = lru_.next; e != &lru_; ) {
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LRUHandle* next = e->next;
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assert(e->refs == 1); // Error if caller has an unreleased handle
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Unref(e);
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e = next;
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}
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}
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void LRUCache::Unref(LRUHandle* e) {
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assert(e->refs > 0);
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e->refs--;
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if (e->refs <= 0) {
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usage_ -= e->charge;
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(*e->deleter)(e->key(), e->value);
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free(e);
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}
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}
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void LRUCache::LRU_Remove(LRUHandle* e) {
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e->next->prev = e->prev;
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e->prev->next = e->next;
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}
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void LRUCache::LRU_Append(LRUHandle* e) {
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// Make "e" newest entry by inserting just before lru_
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e->next = &lru_;
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e->prev = lru_.prev;
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e->prev->next = e;
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e->next->prev = e;
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}
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Cache::Handle* LRUCache::Lookup(const Slice& key) {
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MutexLock l(&mutex_);
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LRUHandle dummy;
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dummy.next = &dummy;
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dummy.value = const_cast<Slice*>(&key);
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HandleTable::iterator iter = table_.find(&dummy);
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if (iter == table_.end()) {
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return NULL;
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} else {
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LRUHandle* e = const_cast<LRUHandle*>(*iter);
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e->refs++;
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LRU_Remove(e);
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LRU_Append(e);
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return reinterpret_cast<Handle*>(e);
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}
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}
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void* LRUCache::Value(Handle* handle) {
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return reinterpret_cast<LRUHandle*>(handle)->value;
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}
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void LRUCache::Release(Handle* handle) {
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MutexLock l(&mutex_);
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Unref(reinterpret_cast<LRUHandle*>(handle));
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}
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Cache::Handle* LRUCache::Insert(const Slice& key, void* value, size_t charge,
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void (*deleter)(const Slice& key, void* value)) {
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MutexLock l(&mutex_);
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LRUHandle* e = reinterpret_cast<LRUHandle*>(
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malloc(sizeof(LRUHandle)-1 + key.size()));
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e->value = value;
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e->deleter = deleter;
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e->charge = charge;
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e->key_length = key.size();
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e->refs = 2; // One from LRUCache, one for the returned handle
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memcpy(e->key_data, key.data(), key.size());
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LRU_Append(e);
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usage_ += charge;
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std::pair<HandleTable::iterator,bool> p = table_.insert(e);
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if (!p.second) {
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// Kill existing entry
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LRUHandle* old = const_cast<LRUHandle*>(*(p.first));
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LRU_Remove(old);
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table_.erase(p.first);
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table_.insert(e);
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Unref(old);
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}
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while (usage_ > capacity_ && lru_.next != &lru_) {
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LRUHandle* old = lru_.next;
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LRU_Remove(old);
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table_.erase(old);
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Unref(old);
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}
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return reinterpret_cast<Handle*>(e);
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}
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void LRUCache::Erase(const Slice& key) {
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MutexLock l(&mutex_);
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LRUHandle dummy;
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dummy.next = &dummy;
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dummy.value = const_cast<Slice*>(&key);
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HandleTable::iterator iter = table_.find(&dummy);
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if (iter != table_.end()) {
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LRUHandle* e = const_cast<LRUHandle*>(*iter);
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LRU_Remove(e);
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table_.erase(iter);
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Unref(e);
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}
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}
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uint64_t LRUCache::NewId() {
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MutexLock l(&mutex_);
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return ++(last_id_);
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}
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} // end anonymous namespace
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Cache* NewLRUCache(size_t capacity) {
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return new LRUCache(capacity);
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}
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}
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