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rocksdb/cache/lru_cache.cc

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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root directory).
//
// 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.
#ifndef __STDC_FORMAT_MACROS
#define __STDC_FORMAT_MACROS
#endif
#include "cache/lru_cache.h"
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <string>
#include "util/mutexlock.h"
namespace rocksdb {
LRUHandleTable::LRUHandleTable() : length_(0), elems_(0), list_(nullptr) {
Resize();
}
LRUHandleTable::~LRUHandleTable() {
ApplyToAllCacheEntries([](LRUHandle* h) {
if (h->refs == 1) {
h->Free();
}
});
delete[] list_;
}
LRUHandle* LRUHandleTable::Lookup(const Slice& key, uint32_t hash) {
return *FindPointer(key, hash);
}
LRUHandle* LRUHandleTable::Insert(LRUHandle* h) {
LRUHandle** ptr = FindPointer(h->key(), h->hash);
LRUHandle* old = *ptr;
h->next_hash = (old == nullptr ? nullptr : old->next_hash);
*ptr = h;
if (old == nullptr) {
++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* LRUHandleTable::Remove(const Slice& key, uint32_t hash) {
LRUHandle** ptr = FindPointer(key, hash);
LRUHandle* result = *ptr;
if (result != nullptr) {
*ptr = result->next_hash;
--elems_;
}
return result;
}
LRUHandle** LRUHandleTable::FindPointer(const Slice& key, uint32_t hash) {
LRUHandle** ptr = &list_[hash & (length_ - 1)];
while (*ptr != nullptr && ((*ptr)->hash != hash || key != (*ptr)->key())) {
ptr = &(*ptr)->next_hash;
}
return ptr;
}
void LRUHandleTable::Resize() {
uint32_t new_length = 16;
while (new_length < elems_ * 1.5) {
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 != nullptr) {
LRUHandle* next = h->next_hash;
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;
}
LRUCacheShard::LRUCacheShard()
: usage_(0), lru_usage_(0), high_pri_pool_usage_(0) {
// Make empty circular linked list
lru_.next = &lru_;
lru_.prev = &lru_;
lru_low_pri_ = &lru_;
}
LRUCacheShard::~LRUCacheShard() {}
bool LRUCacheShard::Unref(LRUHandle* e) {
assert(e->refs > 0);
e->refs--;
return e->refs == 0;
}
// Call deleter and free
void LRUCacheShard::EraseUnRefEntries() {
autovector<LRUHandle*> last_reference_list;
{
MutexLock l(&mutex_);
while (lru_.next != &lru_) {
LRUHandle* old = lru_.next;
assert(old->InCache());
assert(old->refs ==
1); // LRU list contains elements which may be evicted
LRU_Remove(old);
table_.Remove(old->key(), old->hash);
old->SetInCache(false);
Unref(old);
usage_ -= old->charge;
last_reference_list.push_back(old);
}
}
for (auto entry : last_reference_list) {
entry->Free();
}
}
void LRUCacheShard::ApplyToAllCacheEntries(void (*callback)(void*, size_t),
bool thread_safe) {
if (thread_safe) {
mutex_.Lock();
}
table_.ApplyToAllCacheEntries(
[callback](LRUHandle* h) { callback(h->value, h->charge); });
if (thread_safe) {
mutex_.Unlock();
}
}
void LRUCacheShard::TEST_GetLRUList(LRUHandle** lru, LRUHandle** lru_low_pri) {
*lru = &lru_;
*lru_low_pri = lru_low_pri_;
}
size_t LRUCacheShard::TEST_GetLRUSize() {
LRUHandle* lru_handle = lru_.next;
size_t lru_size = 0;
while (lru_handle != &lru_) {
lru_size++;
lru_handle = lru_handle->next;
}
return lru_size;
}
void LRUCacheShard::LRU_Remove(LRUHandle* e) {
assert(e->next != nullptr);
assert(e->prev != nullptr);
if (lru_low_pri_ == e) {
lru_low_pri_ = e->prev;
}
e->next->prev = e->prev;
e->prev->next = e->next;
e->prev = e->next = nullptr;
lru_usage_ -= e->charge;
if (e->InHighPriPool()) {
assert(high_pri_pool_usage_ >= e->charge);
high_pri_pool_usage_ -= e->charge;
}
}
void LRUCacheShard::LRU_Insert(LRUHandle* e) {
assert(e->next == nullptr);
assert(e->prev == nullptr);
if (high_pri_pool_ratio_ > 0 && e->IsHighPri()) {
// Inset "e" to head of LRU list.
e->next = &lru_;
e->prev = lru_.prev;
e->prev->next = e;
e->next->prev = e;
e->SetInHighPriPool(true);
high_pri_pool_usage_ += e->charge;
MaintainPoolSize();
} else {
// Insert "e" to the head of low-pri pool. Note that when
// high_pri_pool_ratio is 0, head of low-pri pool is also head of LRU list.
e->next = lru_low_pri_->next;
e->prev = lru_low_pri_;
e->prev->next = e;
e->next->prev = e;
e->SetInHighPriPool(false);
lru_low_pri_ = e;
}
lru_usage_ += e->charge;
}
void LRUCacheShard::MaintainPoolSize() {
while (high_pri_pool_usage_ > high_pri_pool_capacity_) {
// Overflow last entry in high-pri pool to low-pri pool.
lru_low_pri_ = lru_low_pri_->next;
assert(lru_low_pri_ != &lru_);
lru_low_pri_->SetInHighPriPool(false);
high_pri_pool_usage_ -= lru_low_pri_->charge;
}
}
void LRUCacheShard::EvictFromLRU(size_t charge,
autovector<LRUHandle*>* deleted) {
while (usage_ + charge > capacity_ && lru_.next != &lru_) {
LRUHandle* old = lru_.next;
assert(old->InCache());
assert(old->refs == 1); // LRU list contains elements which may be evicted
LRU_Remove(old);
table_.Remove(old->key(), old->hash);
old->SetInCache(false);
Unref(old);
usage_ -= old->charge;
deleted->push_back(old);
}
}
void LRUCacheShard::SetCapacity(size_t capacity) {
autovector<LRUHandle*> last_reference_list;
{
MutexLock l(&mutex_);
capacity_ = capacity;
high_pri_pool_capacity_ = capacity_ * high_pri_pool_ratio_;
EvictFromLRU(0, &last_reference_list);
}
// we free the entries here outside of mutex for
// performance reasons
for (auto entry : last_reference_list) {
entry->Free();
}
}
void LRUCacheShard::SetStrictCapacityLimit(bool strict_capacity_limit) {
MutexLock l(&mutex_);
strict_capacity_limit_ = strict_capacity_limit;
}
Cache::Handle* LRUCacheShard::Lookup(const Slice& key, uint32_t hash) {
MutexLock l(&mutex_);
LRUHandle* e = table_.Lookup(key, hash);
if (e != nullptr) {
assert(e->InCache());
if (e->refs == 1) {
LRU_Remove(e);
}
e->refs++;
}
return reinterpret_cast<Cache::Handle*>(e);
}
bool LRUCacheShard::Ref(Cache::Handle* h) {
LRUHandle* handle = reinterpret_cast<LRUHandle*>(h);
MutexLock l(&mutex_);
if (handle->InCache() && handle->refs == 1) {
LRU_Remove(handle);
}
handle->refs++;
return true;
}
void LRUCacheShard::SetHighPriorityPoolRatio(double high_pri_pool_ratio) {
MutexLock l(&mutex_);
high_pri_pool_ratio_ = high_pri_pool_ratio;
high_pri_pool_capacity_ = capacity_ * high_pri_pool_ratio_;
MaintainPoolSize();
}
bool LRUCacheShard::Release(Cache::Handle* handle, bool force_erase) {
if (handle == nullptr) {
return false;
}
LRUHandle* e = reinterpret_cast<LRUHandle*>(handle);
bool last_reference = false;
{
MutexLock l(&mutex_);
last_reference = Unref(e);
if (last_reference) {
usage_ -= e->charge;
}
if (e->refs == 1 && e->InCache()) {
// The item is still in cache, and nobody else holds a reference to it
if (usage_ > capacity_ || force_erase) {
// the cache is full
// The LRU list must be empty since the cache is full
assert(!(usage_ > capacity_) || lru_.next == &lru_);
// take this opportunity and remove the item
table_.Remove(e->key(), e->hash);
e->SetInCache(false);
Unref(e);
usage_ -= e->charge;
last_reference = true;
} else {
// put the item on the list to be potentially freed
LRU_Insert(e);
}
}
}
// free outside of mutex
if (last_reference) {
e->Free();
}
return last_reference;
}
Status LRUCacheShard::Insert(const Slice& key, uint32_t hash, void* value,
size_t charge,
void (*deleter)(const Slice& key, void* value),
Cache::Handle** handle, Cache::Priority priority) {
// Allocate the memory here outside of the mutex
// If the cache is full, we'll have to release it
// It shouldn't happen very often though.
LRUHandle* e = reinterpret_cast<LRUHandle*>(
new char[sizeof(LRUHandle) - 1 + key.size()]);
Status s;
autovector<LRUHandle*> last_reference_list;
e->value = value;
e->deleter = deleter;
e->charge = charge;
e->key_length = key.size();
e->hash = hash;
e->refs = (handle == nullptr
? 1
: 2); // One from LRUCache, one for the returned handle
e->next = e->prev = nullptr;
e->SetInCache(true);
e->SetPriority(priority);
memcpy(e->key_data, key.data(), key.size());
{
MutexLock l(&mutex_);
// Free the space following strict LRU policy until enough space
// is freed or the lru list is empty
EvictFromLRU(charge, &last_reference_list);
if (usage_ - lru_usage_ + charge > capacity_ &&
(strict_capacity_limit_ || handle == nullptr)) {
if (handle == nullptr) {
// Don't insert the entry but still return ok, as if the entry inserted
// into cache and get evicted immediately.
last_reference_list.push_back(e);
} else {
delete[] reinterpret_cast<char*>(e);
*handle = nullptr;
s = Status::Incomplete("Insert failed due to LRU cache being full.");
}
} else {
// insert into the cache
// note that the cache might get larger than its capacity if not enough
// space was freed
LRUHandle* old = table_.Insert(e);
usage_ += e->charge;
if (old != nullptr) {
old->SetInCache(false);
if (Unref(old)) {
usage_ -= old->charge;
// old is on LRU because it's in cache and its reference count
// was just 1 (Unref returned 0)
LRU_Remove(old);
last_reference_list.push_back(old);
}
}
if (handle == nullptr) {
LRU_Insert(e);
} else {
*handle = reinterpret_cast<Cache::Handle*>(e);
}
s = Status::OK();
}
}
// we free the entries here outside of mutex for
// performance reasons
for (auto entry : last_reference_list) {
entry->Free();
}
return s;
}
void LRUCacheShard::Erase(const Slice& key, uint32_t hash) {
LRUHandle* e;
bool last_reference = false;
{
MutexLock l(&mutex_);
e = table_.Remove(key, hash);
if (e != nullptr) {
last_reference = Unref(e);
if (last_reference) {
usage_ -= e->charge;
}
if (last_reference && e->InCache()) {
LRU_Remove(e);
}
e->SetInCache(false);
}
}
// mutex not held here
// last_reference will only be true if e != nullptr
if (last_reference) {
e->Free();
}
}
size_t LRUCacheShard::GetUsage() const {
MutexLock l(&mutex_);
return usage_;
}
size_t LRUCacheShard::GetPinnedUsage() const {
MutexLock l(&mutex_);
assert(usage_ >= lru_usage_);
return usage_ - lru_usage_;
}
std::string LRUCacheShard::GetPrintableOptions() const {
const int kBufferSize = 200;
char buffer[kBufferSize];
{
MutexLock l(&mutex_);
snprintf(buffer, kBufferSize, " high_pri_pool_ratio: %.3lf\n",
high_pri_pool_ratio_);
}
return std::string(buffer);
}
LRUCache::LRUCache(size_t capacity, int num_shard_bits,
bool strict_capacity_limit, double high_pri_pool_ratio)
: ShardedCache(capacity, num_shard_bits, strict_capacity_limit) {
num_shards_ = 1 << num_shard_bits;
shards_ = new LRUCacheShard[num_shards_];
SetCapacity(capacity);
SetStrictCapacityLimit(strict_capacity_limit);
for (int i = 0; i < num_shards_; i++) {
shards_[i].SetHighPriorityPoolRatio(high_pri_pool_ratio);
}
}
LRUCache::~LRUCache() { delete[] shards_; }
CacheShard* LRUCache::GetShard(int shard) {
return reinterpret_cast<CacheShard*>(&shards_[shard]);
}
const CacheShard* LRUCache::GetShard(int shard) const {
return reinterpret_cast<CacheShard*>(&shards_[shard]);
}
void* LRUCache::Value(Handle* handle) {
return reinterpret_cast<const LRUHandle*>(handle)->value;
}
size_t LRUCache::GetCharge(Handle* handle) const {
return reinterpret_cast<const LRUHandle*>(handle)->charge;
}
uint32_t LRUCache::GetHash(Handle* handle) const {
return reinterpret_cast<const LRUHandle*>(handle)->hash;
}
void LRUCache::DisownData() { shards_ = nullptr; }
size_t LRUCache::TEST_GetLRUSize() {
size_t lru_size_of_all_shards = 0;
for (int i = 0; i < num_shards_; i++) {
lru_size_of_all_shards += shards_[i].TEST_GetLRUSize();
}
return lru_size_of_all_shards;
}
std::shared_ptr<Cache> NewLRUCache(size_t capacity, int num_shard_bits,
bool strict_capacity_limit,
double high_pri_pool_ratio) {
if (num_shard_bits >= 20) {
return nullptr; // the cache cannot be sharded into too many fine pieces
}
if (high_pri_pool_ratio < 0.0 || high_pri_pool_ratio > 1.0) {
// invalid high_pri_pool_ratio
return nullptr;
}
if (num_shard_bits < 0) {
num_shard_bits = GetDefaultCacheShardBits(capacity);
}
return std::make_shared<LRUCache>(capacity, num_shard_bits,
strict_capacity_limit, high_pri_pool_ratio);
}
} // namespace rocksdb