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// -*- 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) 2004-2006 Sage Weil <sage@newdream.net>
*
* 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_SHAREDCACHE_H
#define CEPH_SHAREDCACHE_H
#include <map>
#include <list>
#include <memory>
#include <utility>
#include "common/Mutex.h"
#include "common/Cond.h"
template <class K, class V>
class SharedLRU {
typedef std::tr1::shared_ptr<V> VPtr;
typedef std::tr1::weak_ptr<V> WeakVPtr;
Mutex lock;
size_t max_size;
Cond cond;
map<K, typename list<pair<K, VPtr> >::iterator > contents;
list<pair<K, VPtr> > lru;
map<K, WeakVPtr> weak_refs;
void trim_cache(list<VPtr> *to_release) {
while (lru.size() > max_size) {
to_release->push_back(lru.back().second);
lru_remove(lru.back().first);
}
}
void lru_remove(K key) {
if (!contents.count(key))
return;
lru.erase(contents[key]);
contents.erase(key);
}
void lru_add(K key, VPtr val, list<VPtr> *to_release) {
if (contents.count(key)) {
lru.splice(lru.begin(), lru, contents[key]);
} else {
lru.push_front(make_pair(key, val));
contents[key] = lru.begin();
trim_cache(to_release);
}
}
void remove(K key) {
Mutex::Locker l(lock);
weak_refs.erase(key);
cond.Signal();
}
class Cleanup {
public:
SharedLRU<K, V> *cache;
K key;
Cleanup(SharedLRU<K, V> *cache, K key) : cache(cache), key(key) {}
void operator()(V *ptr) {
cache->remove(key);
delete ptr;
}
};
public:
SharedLRU(size_t max_size = 20) : lock("SharedLRU::lock"), max_size(max_size) {}
void set_size(size_t new_size) {
list<VPtr> to_release;
{
Mutex::Locker l(lock);
max_size = new_size;
trim_cache(to_release);
}
}
VPtr lower_bound(K key) {
VPtr val;
list<VPtr> to_release;
{
Mutex::Locker l(lock);
bool retry = false;
do {
retry = false;
if (weak_refs.empty())
break;
typename map<K, WeakVPtr>::iterator i = weak_refs.lower_bound(key);
if (i == weak_refs.end())
--i;
val = i->second.lock();
if (val) {
lru_add(i->first, val, &to_release);
} else {
retry = true;
}
if (retry)
cond.Wait(lock);
} while (retry);
}
return val;
}
VPtr lookup(K key) {
VPtr val;
list<VPtr> to_release;
{
Mutex::Locker l(lock);
bool retry = false;
do {
retry = false;
if (weak_refs.count(key)) {
val = weak_refs[key].lock();
if (val) {
lru_add(key, val, &to_release);
} else {
retry = true;
}
}
if (retry)
cond.Wait(lock);
} while (retry);
}
return val;
}
VPtr add(K key, V *value) {
VPtr val(value, Cleanup(this, key));
list<VPtr> to_release;
{
Mutex::Locker l(lock);
weak_refs.insert(make_pair(key, val));
lru_add(key, val, &to_release);
}
return val;
}
};
#endif
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