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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 ceph::shared_ptr<V> VPtr;
typedef ceph::weak_ptr<V> WeakVPtr;
Mutex lock;
size_t max_size;
Cond cond;
unsigned size;
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 (size > max_size) {
to_release->push_back(lru.back().second);
lru_remove(lru.back().first);
}
}
void lru_remove(K key) {
typename map<K, typename list<pair<K, VPtr> >::iterator>::iterator i =
contents.find(key);
if (i == contents.end())
return;
lru.erase(i->second);
--size;
contents.erase(i);
}
void lru_add(K key, VPtr val, list<VPtr> *to_release) {
typename map<K, typename list<pair<K, VPtr> >::iterator>::iterator i =
contents.find(key);
if (i != contents.end()) {
lru.splice(lru.begin(), lru, i->second);
} else {
++size;
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), size(0) {}
~SharedLRU() {
contents.clear();
lru.clear();
assert(weak_refs.empty());
}
void clear(K key) {
VPtr val; // release any ref we have after we drop the lock
{
Mutex::Locker l(lock);
if (weak_refs.count(key)) {
val = weak_refs[key].lock();
}
lru_remove(key);
}
}
void set_size(size_t new_size) {
list<VPtr> to_release;
{
Mutex::Locker l(lock);
max_size = new_size;
trim_cache(&to_release);
}
}
// Returns K key s.t. key <= k for all currently cached k,v
K cached_key_lower_bound() {
Mutex::Locker l(lock);
return weak_refs.begin()->first;
}
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;
typename map<K, WeakVPtr>::iterator i = weak_refs.find(key);
if (i != weak_refs.end()) {
val = i->second.lock();
if (val) {
lru_add(key, val, &to_release);
} else {
retry = true;
}
}
if (retry)
cond.Wait(lock);
} while (retry);
}
return val;
}
/***
* Inserts a key if not present, or bumps it to the front of the LRU if
* it is, and then gives you a reference to the value. If the key already
* existed, you are responsible for deleting the new value you tried to
* insert.
*
* @param key The key to insert
* @param value The value that goes with the key
* @param existed Set to true if the value was already in the
* map, false otherwise
* @return A reference to the map's value for the given key
*/
VPtr add(K key, V *value, bool *existed = NULL) {
VPtr val(value, Cleanup(this, key));
list<VPtr> to_release;
{
Mutex::Locker l(lock);
typename map<K, WeakVPtr>::iterator actual = weak_refs.lower_bound(key);
if (actual != weak_refs.end() && actual->first == key) {
if (existed)
*existed = true;
return actual->second.lock();
}
if (existed)
*existed = false;
weak_refs.insert(actual, make_pair(key, val));
lru_add(key, val, &to_release);
}
return val;
}
};
#endif
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