+++ /dev/null
-// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
-// vim: ts=8 sw=2 smarttab
-/*
- * Ceph - scalable distributed file system
- *
- * Copyright (C) 2014 UnitedStack <haomai@unitedstack.com>
- *
- * Author: Haomai Wang <haomaiwang@gmail.com>
- *
- * This is free software; you can redistribute it and/or
- * modify it under the terms of the GNU Lesser General Public
- * License version 2.1, as published by the Free Software
- * Foundation. See file COPYING.
- *
- */
-
-#ifndef CEPH_RANDOMCACHE_H
-#define CEPH_RANDOMCACHE_H
-
-#include "common/Mutex.h"
-#include "include/compat.h"
-#include "include/unordered_map.h"
-
-
-// Although This is a ramdom cache implementation, here still consider to make
-// the trim progress more reasonable. Each item owns its lookup frequency,
-// when the cache is full it will randomly pick up several items and compare the
-// frequency associated with. The least frequency of items will be evicted.
-template <class K, class V>
-class RandomCache {
- // The first element of pair is the frequency of item, it's used to evict item
- ceph::unordered_map<K, pair<uint64_t, V> > contents;
- Mutex lock;
- uint64_t max_size;
- K last_trim_key;
-
- // When cache reach full, consider to evict a certain number of items
- static const uint64_t EVICT_COUNT = 5;
- // Avoid too much overhead on comparing items's frequency, the number of
- // compare items is expected to small.
- static const uint64_t COMPARE_COUNT = 3;
-
- // In order to make evict cache progress more lightweight and effective,
- // several items are expected to evicted in one call
- void trim_cache(uint64_t evict_count) {
- typename ceph::unordered_map<K, pair<uint64_t, V> >::iterator it = contents.find(last_trim_key);
- uint64_t total_compare = evict_count * COMPARE_COUNT;
- map<uint64_t, K> candidates;
-
- while (total_compare--) {
- if (it == contents.end()) {
- it = contents.begin();
- }
-
- candidates[it->second.first] = it->first;
- it++;
- }
- if (it != contents.end())
- last_trim_key = it->first;
- else
- last_trim_key = contents.begin()->first;
-
- for (typename map<uint64_t, K>::iterator j = candidates.begin(); j != candidates.end(); j++) {
- contents.erase(j->second);
- evict_count--;
- if (!evict_count)
- break;
- }
- }
-
- public:
- RandomCache(size_t max_size=20) : lock("RandomCache::lock"),
- max_size(max_size) {}
- ~RandomCache() {
- contents.clear();
- }
-
- void clear(K key) {
- Mutex::Locker l(lock);
- contents.erase(key);
- }
-
- void set_size(size_t new_size) {
- Mutex::Locker l(lock);
- max_size = new_size;
- if (max_size <= contents.size()) {
- trim_cache(contents.size() - max_size);
- }
- }
-
- bool lookup(K key, V *out) {
- Mutex::Locker l(lock);
- typename ceph::unordered_map<K, pair<uint64_t, V> >::iterator it = contents.find(key);
- if (it != contents.end()) {
- it->second.first++;
- *out = it->second.second;
- return true;
- }
- return false;
- }
-
- void add(K key, V value) {
- Mutex::Locker l(lock);
- if (max_size <= contents.size()) {
- trim_cache(EVICT_COUNT);
- }
- contents[key] = make_pair(1, value);
- }
-};
-
-#endif