You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
288 lines
7.0 KiB
288 lines
7.0 KiB
// 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;
|
|
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);
|
|
}
|
|
}
|
|
};
|
|
|
|
// 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(LRUHandle* h) {
|
|
return *FindPointer(h);
|
|
}
|
|
|
|
LRUHandle* Insert(LRUHandle* h) {
|
|
LRUHandle** ptr = FindPointer(h);
|
|
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(LRUHandle* h) {
|
|
LRUHandle** ptr = FindPointer(h);
|
|
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 *h. If there is no such cache entry, return a pointer to
|
|
// the trailing slot in the corresponding linked list.
|
|
LRUHandle** FindPointer(LRUHandle* h) {
|
|
Slice key = h->key();
|
|
uint32_t hash = Hash(key.data(), key.size(), 0);
|
|
LRUHandle** ptr = &list_[hash & (length_ - 1)];
|
|
while (*ptr != NULL && 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 = Hash(key.data(), key.size(), 0);
|
|
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;
|
|
}
|
|
};
|
|
|
|
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() {
|
|
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);
|
|
LRUHandle* e = table_.Lookup(&dummy);
|
|
if (e != NULL) {
|
|
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;
|
|
|
|
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);
|
|
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);
|
|
LRUHandle* e = table_.Remove(&dummy);
|
|
if (e != NULL) {
|
|
LRU_Remove(e);
|
|
Unref(e);
|
|
}
|
|
}
|
|
|
|
uint64_t LRUCache::NewId() {
|
|
MutexLock l(&mutex_);
|
|
return ++(last_id_);
|
|
}
|
|
|
|
} // end anonymous namespace
|
|
|
|
Cache* NewLRUCache(size_t capacity) {
|
|
return new LRUCache(capacity);
|
|
}
|
|
|
|
}
|