mirror of
https://github.com/Xahau/xahaud.git
synced 2025-12-06 17:27:52 +00:00
Squashed 'src/rocksdb/' content from commit 224932d
git-subtree-dir: src/rocksdb git-subtree-split: 224932d4d0b561712107d747c662df181c39644d
This commit is contained in:
Vinnie Falco
481
util/cache.cc
Normal file
481
util/cache.cc
Normal file
@@ -0,0 +1,481 @@
|
||||
// Copyright (c) 2013, Facebook, Inc. All rights reserved.
|
||||
// This source code is licensed under the BSD-style license found in the
|
||||
// LICENSE file in the root directory of this source tree. An additional grant
|
||||
// of patent rights can be found in the PATENTS file in the same 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.
|
||||
|
||||
#include <assert.h>
|
||||
#include <stdio.h>
|
||||
#include <stdlib.h>
|
||||
|
||||
#include "rocksdb/cache.h"
|
||||
#include "port/port.h"
|
||||
#include "util/autovector.h"
|
||||
#include "util/hash.h"
|
||||
#include "util/mutexlock.h"
|
||||
|
||||
namespace rocksdb {
|
||||
|
||||
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_(nullptr) { 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 == 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* 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;
|
||||
}
|
||||
|
||||
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 != nullptr &&
|
||||
((*ptr)->hash != hash || key != (*ptr)->key())) {
|
||||
ptr = &(*ptr)->next_hash;
|
||||
}
|
||||
return ptr;
|
||||
}
|
||||
|
||||
void 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;
|
||||
}
|
||||
};
|
||||
|
||||
// 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; }
|
||||
void SetRemoveScanCountLimit(size_t remove_scan_count_limit) {
|
||||
remove_scan_count_limit_ = remove_scan_count_limit;
|
||||
}
|
||||
|
||||
// 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);
|
||||
// Although in some platforms the update of size_t is atomic, to make sure
|
||||
// GetUsage() works correctly under any platforms, we'll protect this
|
||||
// function with mutex.
|
||||
size_t GetUsage() const {
|
||||
MutexLock l(&mutex_);
|
||||
return usage_;
|
||||
}
|
||||
|
||||
void ApplyToAllCacheEntries(void (*callback)(void*, size_t),
|
||||
bool thread_safe);
|
||||
|
||||
private:
|
||||
void LRU_Remove(LRUHandle* e);
|
||||
void LRU_Append(LRUHandle* e);
|
||||
// Just reduce the reference count by 1.
|
||||
// Return true if last reference
|
||||
bool Unref(LRUHandle* e);
|
||||
// Call deleter and free
|
||||
void FreeEntry(LRUHandle* e);
|
||||
|
||||
// Initialized before use.
|
||||
size_t capacity_;
|
||||
uint32_t remove_scan_count_limit_;
|
||||
|
||||
// mutex_ protects the following state.
|
||||
// We don't count mutex_ as the cache's internal state so semantically we
|
||||
// don't mind mutex_ invoking the non-const actions.
|
||||
mutable port::Mutex mutex_;
|
||||
size_t usage_;
|
||||
|
||||
// Dummy head of LRU list.
|
||||
// lru.prev is newest entry, lru.next is oldest entry.
|
||||
LRUHandle lru_;
|
||||
|
||||
HandleTable table_;
|
||||
};
|
||||
|
||||
LRUCache::LRUCache()
|
||||
: usage_(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
|
||||
if (Unref(e)) {
|
||||
FreeEntry(e);
|
||||
}
|
||||
e = next;
|
||||
}
|
||||
}
|
||||
|
||||
bool LRUCache::Unref(LRUHandle* e) {
|
||||
assert(e->refs > 0);
|
||||
e->refs--;
|
||||
return e->refs == 0;
|
||||
}
|
||||
|
||||
void LRUCache::FreeEntry(LRUHandle* e) {
|
||||
assert(e->refs == 0);
|
||||
(*e->deleter)(e->key(), e->value);
|
||||
free(e);
|
||||
}
|
||||
|
||||
void LRUCache::ApplyToAllCacheEntries(void (*callback)(void*, size_t),
|
||||
bool thread_safe) {
|
||||
if (thread_safe) {
|
||||
mutex_.Lock();
|
||||
}
|
||||
for (auto e = lru_.next; e != &lru_; e = e->next) {
|
||||
callback(e->value, e->charge);
|
||||
}
|
||||
if (thread_safe) {
|
||||
mutex_.Unlock();
|
||||
}
|
||||
}
|
||||
|
||||
void LRUCache::LRU_Remove(LRUHandle* e) {
|
||||
e->next->prev = e->prev;
|
||||
e->prev->next = e->next;
|
||||
usage_ -= e->charge;
|
||||
}
|
||||
|
||||
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;
|
||||
usage_ += e->charge;
|
||||
}
|
||||
|
||||
Cache::Handle* LRUCache::Lookup(const Slice& key, uint32_t hash) {
|
||||
MutexLock l(&mutex_);
|
||||
LRUHandle* e = table_.Lookup(key, hash);
|
||||
if (e != nullptr) {
|
||||
e->refs++;
|
||||
LRU_Remove(e);
|
||||
LRU_Append(e);
|
||||
}
|
||||
return reinterpret_cast<Cache::Handle*>(e);
|
||||
}
|
||||
|
||||
void LRUCache::Release(Cache::Handle* handle) {
|
||||
LRUHandle* e = reinterpret_cast<LRUHandle*>(handle);
|
||||
bool last_reference = false;
|
||||
{
|
||||
MutexLock l(&mutex_);
|
||||
last_reference = Unref(e);
|
||||
}
|
||||
if (last_reference) {
|
||||
FreeEntry(e);
|
||||
}
|
||||
}
|
||||
|
||||
Cache::Handle* LRUCache::Insert(
|
||||
const Slice& key, uint32_t hash, void* value, size_t charge,
|
||||
void (*deleter)(const Slice& key, void* value)) {
|
||||
|
||||
LRUHandle* e = reinterpret_cast<LRUHandle*>(
|
||||
malloc(sizeof(LRUHandle)-1 + key.size()));
|
||||
autovector<LRUHandle*> last_reference_list;
|
||||
|
||||
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());
|
||||
|
||||
{
|
||||
MutexLock l(&mutex_);
|
||||
|
||||
LRU_Append(e);
|
||||
|
||||
LRUHandle* old = table_.Insert(e);
|
||||
if (old != nullptr) {
|
||||
LRU_Remove(old);
|
||||
if (Unref(old)) {
|
||||
last_reference_list.push_back(old);
|
||||
}
|
||||
}
|
||||
|
||||
if (remove_scan_count_limit_ > 0) {
|
||||
// Try to free the space by evicting the entries that are only
|
||||
// referenced by the cache first.
|
||||
LRUHandle* cur = lru_.next;
|
||||
for (unsigned int scanCount = 0;
|
||||
usage_ > capacity_ && cur != &lru_
|
||||
&& scanCount < remove_scan_count_limit_; scanCount++) {
|
||||
LRUHandle* next = cur->next;
|
||||
if (cur->refs <= 1) {
|
||||
LRU_Remove(cur);
|
||||
table_.Remove(cur->key(), cur->hash);
|
||||
if (Unref(cur)) {
|
||||
last_reference_list.push_back(cur);
|
||||
}
|
||||
}
|
||||
cur = next;
|
||||
}
|
||||
}
|
||||
|
||||
// Free the space following strict LRU policy until enough space
|
||||
// is freed.
|
||||
while (usage_ > capacity_ && lru_.next != &lru_) {
|
||||
LRUHandle* old = lru_.next;
|
||||
LRU_Remove(old);
|
||||
table_.Remove(old->key(), old->hash);
|
||||
if (Unref(old)) {
|
||||
last_reference_list.push_back(old);
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
// we free the entries here outside of mutex for
|
||||
// performance reasons
|
||||
for (auto entry : last_reference_list) {
|
||||
FreeEntry(entry);
|
||||
}
|
||||
|
||||
return reinterpret_cast<Cache::Handle*>(e);
|
||||
}
|
||||
|
||||
void LRUCache::Erase(const Slice& key, uint32_t hash) {
|
||||
LRUHandle* e;
|
||||
bool last_reference = false;
|
||||
{
|
||||
MutexLock l(&mutex_);
|
||||
e = table_.Remove(key, hash);
|
||||
if (e != nullptr) {
|
||||
LRU_Remove(e);
|
||||
last_reference = Unref(e);
|
||||
}
|
||||
}
|
||||
// mutex not held here
|
||||
// last_reference will only be true if e != nullptr
|
||||
if (last_reference) {
|
||||
FreeEntry(e);
|
||||
}
|
||||
}
|
||||
|
||||
static int kNumShardBits = 4; // default values, can be overridden
|
||||
static int kRemoveScanCountLimit = 0; // default values, can be overridden
|
||||
|
||||
class ShardedLRUCache : public Cache {
|
||||
private:
|
||||
LRUCache* shards_;
|
||||
port::Mutex id_mutex_;
|
||||
uint64_t last_id_;
|
||||
int num_shard_bits_;
|
||||
size_t capacity_;
|
||||
|
||||
static inline uint32_t HashSlice(const Slice& s) {
|
||||
return Hash(s.data(), s.size(), 0);
|
||||
}
|
||||
|
||||
uint32_t Shard(uint32_t hash) {
|
||||
// Note, hash >> 32 yields hash in gcc, not the zero we expect!
|
||||
return (num_shard_bits_ > 0) ? (hash >> (32 - num_shard_bits_)) : 0;
|
||||
}
|
||||
|
||||
void init(size_t capacity, int numbits, int removeScanCountLimit) {
|
||||
num_shard_bits_ = numbits;
|
||||
capacity_ = capacity;
|
||||
int num_shards = 1 << num_shard_bits_;
|
||||
shards_ = new LRUCache[num_shards];
|
||||
const size_t per_shard = (capacity + (num_shards - 1)) / num_shards;
|
||||
for (int s = 0; s < num_shards; s++) {
|
||||
shards_[s].SetCapacity(per_shard);
|
||||
shards_[s].SetRemoveScanCountLimit(removeScanCountLimit);
|
||||
}
|
||||
}
|
||||
|
||||
public:
|
||||
explicit ShardedLRUCache(size_t capacity)
|
||||
: last_id_(0) {
|
||||
init(capacity, kNumShardBits, kRemoveScanCountLimit);
|
||||
}
|
||||
ShardedLRUCache(size_t capacity, int num_shard_bits,
|
||||
int removeScanCountLimit)
|
||||
: last_id_(0) {
|
||||
init(capacity, num_shard_bits, removeScanCountLimit);
|
||||
}
|
||||
virtual ~ShardedLRUCache() {
|
||||
delete[] shards_;
|
||||
}
|
||||
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 shards_[Shard(hash)].Insert(key, hash, value, charge, deleter);
|
||||
}
|
||||
virtual Handle* Lookup(const Slice& key) {
|
||||
const uint32_t hash = HashSlice(key);
|
||||
return shards_[Shard(hash)].Lookup(key, hash);
|
||||
}
|
||||
virtual void Release(Handle* handle) {
|
||||
LRUHandle* h = reinterpret_cast<LRUHandle*>(handle);
|
||||
shards_[Shard(h->hash)].Release(handle);
|
||||
}
|
||||
virtual void Erase(const Slice& key) {
|
||||
const uint32_t hash = HashSlice(key);
|
||||
shards_[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_);
|
||||
}
|
||||
virtual size_t GetCapacity() const {
|
||||
return capacity_;
|
||||
}
|
||||
|
||||
virtual size_t GetUsage() const {
|
||||
// We will not lock the cache when getting the usage from shards.
|
||||
// for (size_t i = 0; i < num_shard_bits_; ++i)
|
||||
int num_shards = 1 << num_shard_bits_;
|
||||
size_t usage = 0;
|
||||
for (int s = 0; s < num_shards; s++) {
|
||||
usage += shards_[s].GetUsage();
|
||||
}
|
||||
return usage;
|
||||
}
|
||||
|
||||
virtual void DisownData() {
|
||||
shards_ = nullptr;
|
||||
}
|
||||
|
||||
virtual void ApplyToAllCacheEntries(void (*callback)(void*, size_t),
|
||||
bool thread_safe) override {
|
||||
int num_shards = 1 << num_shard_bits_;
|
||||
for (int s = 0; s < num_shards; s++) {
|
||||
shards_[s].ApplyToAllCacheEntries(callback, thread_safe);
|
||||
}
|
||||
}
|
||||
};
|
||||
|
||||
} // end anonymous namespace
|
||||
|
||||
shared_ptr<Cache> NewLRUCache(size_t capacity) {
|
||||
return NewLRUCache(capacity, kNumShardBits);
|
||||
}
|
||||
|
||||
shared_ptr<Cache> NewLRUCache(size_t capacity, int num_shard_bits) {
|
||||
return NewLRUCache(capacity, num_shard_bits, kRemoveScanCountLimit);
|
||||
}
|
||||
|
||||
shared_ptr<Cache> NewLRUCache(size_t capacity, int num_shard_bits,
|
||||
int removeScanCountLimit) {
|
||||
if (num_shard_bits >= 20) {
|
||||
return nullptr; // the cache cannot be sharded into too many fine pieces
|
||||
}
|
||||
return std::make_shared<ShardedLRUCache>(capacity,
|
||||
num_shard_bits,
|
||||
removeScanCountLimit);
|
||||
}
|
||||
|
||||
} // namespace rocksdb
|
||||
Reference in New Issue
Block a user