191 lines
6.7 KiB
C
191 lines
6.7 KiB
C
|
// Copyright (c) 2011-present, 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.
|
||
|
#pragma once
|
||
|
|
||
|
#include "util/sharded_cache.h"
|
||
|
|
||
|
#include "port/port.h"
|
||
|
#include "util/autovector.h"
|
||
|
|
||
|
namespace rocksdb {
|
||
|
|
||
|
// LRU cache implementation
|
||
|
|
||
|
// An entry is a variable length heap-allocated structure.
|
||
|
// Entries are referenced by cache and/or by any external entity.
|
||
|
// The cache keeps all its entries in table. Some elements
|
||
|
// are also stored on LRU list.
|
||
|
//
|
||
|
// LRUHandle can be in these states:
|
||
|
// 1. Referenced externally AND in hash table.
|
||
|
// In that case the entry is *not* in the LRU. (refs > 1 && in_cache == true)
|
||
|
// 2. Not referenced externally and in hash table. In that case the entry is
|
||
|
// in the LRU and can be freed. (refs == 1 && in_cache == true)
|
||
|
// 3. Referenced externally and not in hash table. In that case the entry is
|
||
|
// in not on LRU and not in table. (refs >= 1 && in_cache == false)
|
||
|
//
|
||
|
// All newly created LRUHandles are in state 1. If you call
|
||
|
// LRUCacheShard::Release
|
||
|
// on entry in state 1, it will go into state 2. To move from state 1 to
|
||
|
// state 3, either call LRUCacheShard::Erase or LRUCacheShard::Insert with the
|
||
|
// same key.
|
||
|
// To move from state 2 to state 1, use LRUCacheShard::Lookup.
|
||
|
// Before destruction, make sure that no handles are in state 1. This means
|
||
|
// that any successful LRUCacheShard::Lookup/LRUCacheShard::Insert have a
|
||
|
// matching
|
||
|
// RUCache::Release (to move into state 2) or LRUCacheShard::Erase (for state 3)
|
||
|
|
||
|
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; // a number of refs to this entry
|
||
|
// cache itself is counted as 1
|
||
|
bool in_cache; // true, if this entry is referenced by the hash table
|
||
|
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);
|
||
|
}
|
||
|
}
|
||
|
|
||
|
void Free() {
|
||
|
assert((refs == 1 && in_cache) || (refs == 0 && !in_cache));
|
||
|
(*deleter)(key(), value);
|
||
|
delete[] reinterpret_cast<char*>(this);
|
||
|
}
|
||
|
};
|
||
|
|
||
|
// 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 LRUHandleTable {
|
||
|
public:
|
||
|
LRUHandleTable();
|
||
|
~LRUHandleTable();
|
||
|
|
||
|
LRUHandle* Lookup(const Slice& key, uint32_t hash);
|
||
|
LRUHandle* Insert(LRUHandle* h);
|
||
|
LRUHandle* Remove(const Slice& key, uint32_t hash);
|
||
|
|
||
|
template <typename T>
|
||
|
void ApplyToAllCacheEntries(T func) {
|
||
|
for (uint32_t i = 0; i < length_; i++) {
|
||
|
LRUHandle* h = list_[i];
|
||
|
while (h != nullptr) {
|
||
|
auto n = h->next_hash;
|
||
|
assert(h->in_cache);
|
||
|
func(h);
|
||
|
h = n;
|
||
|
}
|
||
|
}
|
||
|
}
|
||
|
|
||
|
private:
|
||
|
// 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);
|
||
|
|
||
|
void Resize();
|
||
|
|
||
|
// 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_;
|
||
|
};
|
||
|
|
||
|
// A single shard of sharded cache.
|
||
|
class LRUCacheShard : public CacheShard {
|
||
|
public:
|
||
|
LRUCacheShard();
|
||
|
virtual ~LRUCacheShard();
|
||
|
|
||
|
// Separate from constructor so caller can easily make an array of LRUCache
|
||
|
// if current usage is more than new capacity, the function will attempt to
|
||
|
// free the needed space
|
||
|
virtual void SetCapacity(size_t capacity) override;
|
||
|
|
||
|
// Set the flag to reject insertion if cache if full.
|
||
|
virtual void SetStrictCapacityLimit(bool strict_capacity_limit) override;
|
||
|
|
||
|
// Like Cache methods, but with an extra "hash" parameter.
|
||
|
virtual Status Insert(const Slice& key, uint32_t hash, void* value,
|
||
|
size_t charge,
|
||
|
void (*deleter)(const Slice& key, void* value),
|
||
|
Cache::Handle** handle) override;
|
||
|
virtual Cache::Handle* Lookup(const Slice& key, uint32_t hash) override;
|
||
|
virtual void Release(Cache::Handle* handle) override;
|
||
|
virtual void Erase(const Slice& key, uint32_t hash) override;
|
||
|
|
||
|
// Although in some platforms the update of size_t is atomic, to make sure
|
||
|
// GetUsage() and GetPinnedUsage() work correctly under any platform, we'll
|
||
|
// protect them with mutex_.
|
||
|
|
||
|
virtual size_t GetUsage() const override;
|
||
|
virtual size_t GetPinnedUsage() const override;
|
||
|
|
||
|
virtual void ApplyToAllCacheEntries(void (*callback)(void*, size_t),
|
||
|
bool thread_safe) override;
|
||
|
|
||
|
virtual void EraseUnRefEntries() override;
|
||
|
|
||
|
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);
|
||
|
|
||
|
// Free some space following strict LRU policy until enough space
|
||
|
// to hold (usage_ + charge) is freed or the lru list is empty
|
||
|
// This function is not thread safe - it needs to be executed while
|
||
|
// holding the mutex_
|
||
|
void EvictFromLRU(size_t charge, autovector<LRUHandle*>* deleted);
|
||
|
|
||
|
// Initialized before use.
|
||
|
size_t capacity_;
|
||
|
|
||
|
// Memory size for entries residing in the cache
|
||
|
size_t usage_;
|
||
|
|
||
|
// Memory size for entries residing only in the LRU list
|
||
|
size_t lru_usage_;
|
||
|
|
||
|
// Whether to reject insertion if cache reaches its full capacity.
|
||
|
bool strict_capacity_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_;
|
||
|
|
||
|
// Dummy head of LRU list.
|
||
|
// lru.prev is newest entry, lru.next is oldest entry.
|
||
|
// LRU contains items which can be evicted, ie reference only by cache
|
||
|
LRUHandle lru_;
|
||
|
|
||
|
LRUHandleTable table_;
|
||
|
};
|
||
|
|
||
|
} // namespace rocksdb
|