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.
99 rivejä
3.4 KiB
99 rivejä
3.4 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.
|
|
//
|
|
// A Cache is an interface that maps keys to values. It has internal
|
|
// synchronization and may be safely accessed concurrently from
|
|
// multiple threads. It may automatically evict entries to make room
|
|
// for new entries. Values have a specified charge against the cache
|
|
// capacity. For example, a cache where the values are variable
|
|
// length strings, may use the length of the string as the charge for
|
|
// the string.
|
|
//
|
|
// A builtin cache implementation with a least-recently-used eviction
|
|
// policy is provided. Clients may use their own implementations if
|
|
// they want something more sophisticated (like scan-resistance, a
|
|
// custom eviction policy, variable cache sizing, etc.)
|
|
|
|
#ifndef STORAGE_LEVELDB_INCLUDE_CACHE_H_
|
|
#define STORAGE_LEVELDB_INCLUDE_CACHE_H_
|
|
|
|
#include <stdint.h>
|
|
#include "include/slice.h"
|
|
|
|
namespace leveldb {
|
|
|
|
class Cache;
|
|
|
|
// Create a new cache with a fixed size capacity. This implementation
|
|
// of Cache uses a least-recently-used eviction policy.
|
|
extern Cache* NewLRUCache(size_t capacity);
|
|
|
|
class Cache {
|
|
public:
|
|
Cache() { }
|
|
|
|
// Destroys all existing entries by calling the "deleter"
|
|
// function that was passed to the constructor.
|
|
virtual ~Cache();
|
|
|
|
// Opaque handle to an entry stored in the cache.
|
|
struct Handle { };
|
|
|
|
// Insert a mapping from key->value into the cache and assign it
|
|
// the specified charge against the total cache capacity.
|
|
//
|
|
// Returns a handle that corresponds to the mapping. The caller
|
|
// must call this->Release(handle) when the returned mapping is no
|
|
// longer needed.
|
|
//
|
|
// When the inserted entry is no longer needed, the key and
|
|
// value will be passed to "deleter".
|
|
virtual Handle* Insert(const Slice& key, void* value, size_t charge,
|
|
void (*deleter)(const Slice& key, void* value)) = 0;
|
|
|
|
// If the cache has no mapping for "key", returns NULL.
|
|
//
|
|
// Else return a handle that corresponds to the mapping. The caller
|
|
// must call this->Release(handle) when the returned mapping is no
|
|
// longer needed.
|
|
virtual Handle* Lookup(const Slice& key) = 0;
|
|
|
|
// Release a mapping returned by a previous Lookup().
|
|
// REQUIRES: handle must not have been released yet.
|
|
// REQUIRES: handle must have been returned by a method on *this.
|
|
virtual void Release(Handle* handle) = 0;
|
|
|
|
// Return the value encapsulated in a handle returned by a
|
|
// successful Lookup().
|
|
// REQUIRES: handle must not have been released yet.
|
|
// REQUIRES: handle must have been returned by a method on *this.
|
|
virtual void* Value(Handle* handle) = 0;
|
|
|
|
// If the cache contains entry for key, erase it. Note that the
|
|
// underlying entry will be kept around until all existing handles
|
|
// to it have been released.
|
|
virtual void Erase(const Slice& key) = 0;
|
|
|
|
// Return a new numeric id. May be used by multiple clients who are
|
|
// sharing the same cache to partition the key space. Typically the
|
|
// client will allocate a new id at startup and prepend the id to
|
|
// its cache keys.
|
|
virtual uint64_t NewId() = 0;
|
|
|
|
private:
|
|
void LRU_Remove(Handle* e);
|
|
void LRU_Append(Handle* e);
|
|
void Unref(Handle* e);
|
|
|
|
struct Rep;
|
|
Rep* rep_;
|
|
|
|
// No copying allowed
|
|
Cache(const Cache&);
|
|
void operator=(const Cache&);
|
|
};
|
|
|
|
}
|
|
|
|
#endif // STORAGE_LEVELDB_UTIL_CACHE_H_
|