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// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
// vim: ts=8 sw=2 smarttab
#pragma once
#include <boost/intrusive_ptr.hpp>
#include <boost/intrusive/set.hpp>
#include <boost/intrusive/list.hpp>
namespace ceph::common {
/**
* intrusive_lru: lru implementation with embedded map and list hook
*
* Note, this implementation currently is entirely thread-unsafe.
*/
template <typename K, typename V, typename VToK>
struct intrusive_lru_config {
using key_type = K;
using value_type = V;
using key_of_value = VToK;
};
template <typename Config>
class intrusive_lru;
template <typename Config>
class intrusive_lru_base;
template <typename Config>
void intrusive_ptr_add_ref(intrusive_lru_base<Config> *p);
template <typename Config>
void intrusive_ptr_release(intrusive_lru_base<Config> *p);
template <typename Config>
class intrusive_lru_base {
unsigned use_count = 0;
// null if unreferenced
intrusive_lru<Config> *lru = nullptr;
public:
boost::intrusive::set_member_hook<> set_hook;
boost::intrusive::list_member_hook<> list_hook;
using Ref = boost::intrusive_ptr<typename Config::value_type>;
using lru_t = intrusive_lru<Config>;
friend intrusive_lru<Config>;
friend void intrusive_ptr_add_ref<>(intrusive_lru_base<Config> *);
friend void intrusive_ptr_release<>(intrusive_lru_base<Config> *);
virtual ~intrusive_lru_base() {}
};
template <typename Config>
class intrusive_lru {
using base_t = intrusive_lru_base<Config>;
using K = typename Config::key_type;
using T = typename Config::value_type;
using TRef = typename base_t::Ref;
using lru_set_option_t = boost::intrusive::member_hook<
base_t,
boost::intrusive::set_member_hook<>,
&base_t::set_hook>;
using VToK = typename Config::key_of_value;
struct VToKWrapped {
using type = typename VToK::type;
const type &operator()(const base_t &obc) {
return VToK()(static_cast<const T&>(obc));
}
};
using lru_set_t = boost::intrusive::set<
base_t,
lru_set_option_t,
boost::intrusive::key_of_value<VToKWrapped>
>;
lru_set_t lru_set;
using lru_list_t = boost::intrusive::list<
base_t,
boost::intrusive::member_hook<
base_t,
boost::intrusive::list_member_hook<>,
&base_t::list_hook>>;
lru_list_t unreferenced_list;
size_t lru_target_size = 0;
void evict() {
while (!unreferenced_list.empty() &&
lru_set.size() > lru_target_size) {
auto &b = unreferenced_list.front();
assert(!b.lru);
unreferenced_list.pop_front();
lru_set.erase_and_dispose(
lru_set.iterator_to(b),
[](auto *p) { delete p; }
);
}
}
void access(base_t &b) {
if (b.lru)
return;
unreferenced_list.erase(lru_list_t::s_iterator_to(b));
b.lru = this;
}
void insert(base_t &b) {
assert(!b.lru);
lru_set.insert(b);
b.lru = this;
evict();
}
void unreferenced(base_t &b) {
assert(b.lru);
unreferenced_list.push_back(b);
b.lru = nullptr;
evict();
}
public:
/**
* Returns the TRef corresponding to k if it exists or
* creates it otherwise. Return is:
* std::pair(reference_to_val, found)
*/
std::pair<TRef, bool> get_or_create(const K &k) {
typename lru_set_t::insert_commit_data icd;
auto [iter, missing] = lru_set.insert_check(
k,
icd);
if (missing) {
auto ret = new T(k);
lru_set.insert_commit(*ret, icd);
insert(*ret);
return {TRef(ret), false};
} else {
access(*iter);
return {TRef(static_cast<T*>(&*iter)), true};
}
}
/**
* Returns the TRef corresponding to k if it exists or
* nullptr otherwise.
*/
TRef get(const K &k) {
if (auto iter = lru_set.find(k); iter != std::end(lru_set)) {
access(*iter);
return TRef(static_cast<T*>(&*iter));
} else {
return nullptr;
}
}
void set_target_size(size_t target_size) {
lru_target_size = target_size;
evict();
}
friend void intrusive_ptr_add_ref<>(intrusive_lru_base<Config> *);
friend void intrusive_ptr_release<>(intrusive_lru_base<Config> *);
};
template <typename Config>
void intrusive_ptr_add_ref(intrusive_lru_base<Config> *p) {
assert(p);
assert(p->lru);
p->use_count++;
}
template <typename Config>
void intrusive_ptr_release(intrusive_lru_base<Config> *p) {
assert(p);
assert(p->use_count > 0);
--p->use_count;
if (p->use_count == 0) {
p->lru->unreferenced(*p);
}
}
}
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