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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.
#if defined(LEVELDB_PLATFORM_POSIX) || defined(LEVELDB_PLATFORM_ANDROID)
#include <unordered_set>
#elif defined(LEVELDB_PLATFORM_CHROMIUM)
#include "base/hash_tables.h"
#else
#include <hash_set> // TODO(sanjay): Switch to unordered_set when possible.
#endif
#include <assert.h>
#include "include/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;
LRUHandle* prev;
size_t charge; // TODO(opt): Only allow uint32_t?
size_t key_length;
size_t refs; // TODO(opt): Pack with "key_length"?
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);
}
}
};
// Pick a platform specific hash_set instantiation
#if defined(LEVELDB_PLATFORM_CHROMIUM) && defined(OS_WIN)
// Microsoft's hash_set deviates from the standard. See
// http://msdn.microsoft.com/en-us/library/1t4xas78(v=vs.80).aspx
// for details. Basically the 2 param () operator is a less than and
// the 1 param () operator is a hash function.
struct HandleHashCompare : public stdext::hash_compare<LRUHandle*> {
size_t operator() (LRUHandle* h) const {
Slice k = h->key();
return Hash(k.data(), k.size(), 0);
}
bool operator() (LRUHandle* a, LRUHandle* b) const {
return a->key().compare(b->key()) < 0;
}
};
typedef base::hash_set<LRUHandle*, HandleHashCompare> HandleTable;
#else
struct HandleHash {
inline size_t operator()(LRUHandle* h) const {
Slice k = h->key();
return Hash(k.data(), k.size(), 0);
}
};
struct HandleEq {
inline bool operator()(LRUHandle* a, LRUHandle* b) const {
return a->key() == b->key();
}
};
# if defined(LEVELDB_PLATFORM_CHROMIUM)
typedef base::hash_set<LRUHandle*, HandleHash, HandleEq> HandleTable;
# elif defined(LEVELDB_PLATFORM_POSIX) || defined(LEVELDB_PLATFORM_ANDROID)
typedef std::unordered_set<LRUHandle*, HandleHash, HandleEq> HandleTable;
# else
typedef __gnu_cxx::hash_set<LRUHandle*, HandleHash, HandleEq> HandleTable;
# endif
#endif
class LRUCache : public Cache {
public:
explicit LRUCache(size_t capacity);
virtual ~LRUCache();
virtual Handle* Insert(const Slice& key, void* value, size_t charge,
void (*deleter)(const Slice& key, void* value));
virtual Handle* Lookup(const Slice& key);
virtual void Release(Handle* handle);
virtual void* Value(Handle* handle);
virtual void Erase(const Slice& key);
virtual uint64_t NewId();
private:
void LRU_Remove(LRUHandle* e);
void LRU_Append(LRUHandle* e);
void Unref(LRUHandle* e);
// Constructor parameters
const 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(size_t capacity)
: capacity_(capacity),
usage_(0),
last_id_(0) {
// Make empty circular linked list
lru_.next = &lru_;
lru_.prev = &lru_;
}
LRUCache::~LRUCache() {
table_.clear();
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) {
MutexLock l(&mutex_);
LRUHandle dummy;
dummy.next = &dummy;
dummy.value = const_cast<Slice*>(&key);
HandleTable::iterator iter = table_.find(&dummy);
if (iter == table_.end()) {
return NULL;
} else {
LRUHandle* e = const_cast<LRUHandle*>(*iter);
e->refs++;
LRU_Remove(e);
LRU_Append(e);
return reinterpret_cast<Handle*>(e);
}
}
void* LRUCache::Value(Handle* handle) {
return reinterpret_cast<LRUHandle*>(handle)->value;
}
void LRUCache::Release(Handle* handle) {
MutexLock l(&mutex_);
Unref(reinterpret_cast<LRUHandle*>(handle));
}
Cache::Handle* LRUCache::Insert(const Slice& key, 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->refs = 2; // One from LRUCache, one for the returned handle
memcpy(e->key_data, key.data(), key.size());
LRU_Append(e);
usage_ += charge;
std::pair<HandleTable::iterator,bool> p = table_.insert(e);
if (!p.second) {
// Kill existing entry
LRUHandle* old = const_cast<LRUHandle*>(*(p.first));
LRU_Remove(old);
table_.erase(p.first);
table_.insert(e);
Unref(old);
}
while (usage_ > capacity_ && lru_.next != &lru_) {
LRUHandle* old = lru_.next;
LRU_Remove(old);
table_.erase(old);
Unref(old);
}
return reinterpret_cast<Handle*>(e);
}
void LRUCache::Erase(const Slice& key) {
MutexLock l(&mutex_);
LRUHandle dummy;
dummy.next = &dummy;
dummy.value = const_cast<Slice*>(&key);
HandleTable::iterator iter = table_.find(&dummy);
if (iter != table_.end()) {
LRUHandle* e = const_cast<LRUHandle*>(*iter);
LRU_Remove(e);
table_.erase(iter);
Unref(e);
}
}
uint64_t LRUCache::NewId() {
MutexLock l(&mutex_);
return ++(last_id_);
}
} // end anonymous namespace
Cache* NewLRUCache(size_t capacity) {
return new LRUCache(capacity);
}
}