Feature/sessions cache (#2040)

* cache

Signed-off-by: iceseer <iceseer@gmail.com>

---------

Signed-off-by: iceseer <iceseer@gmail.com>

core/common/ref_cache.hpp

@@ -0,0 +1,121 @@
+/**
+ * Copyright Quadrivium LLC
+ * All Rights Reserved
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#pragma once
+
+#include <map>
+#include <memory>
+#include <optional>
+
+namespace kagome {
+
+ /**
+ * @brief Cache keeps an item inside if any reference exists. If all
+ * references lost, then item removes from cache. If an item exists, then it
+ * returns new reference on it.
+ */
+ template <typename K, typename V>
+ struct RefCache : std::enable_shared_from_this<RefCache<K, V>> {
+ struct RefObj;
+
+ using Value = std::decay_t<V>;
+ using Container = std::map<K, std::weak_ptr<RefObj>>;
+ using Iterator = typename Container::iterator;
+ using SRefCache = std::shared_ptr<RefCache>;
+ using Key = K;
+
+ struct RefObj {
+ template <typename... Args>
+ RefObj(Args &&...args) : obj_(std::forward<Args>(args)...) {}
+
+ RefObj(RefObj &&) = default;
+ RefObj(const RefObj &) = delete;
+
+ RefObj &operator=(RefObj &&) = delete;
+ RefObj &operator=(const RefObj &) = delete;
+
+ ~RefObj() {
+ if (keeper_) {
+ keeper_->remove(it_);
+ }
+ }
+
+ Value &value_mut() {
+ return obj_;
+ }
+
+ const Value &value() const {
+ return obj_;
+ }
+
+ private:
+ void store_internal_refs(Iterator it, SRefCache keeper) {
+ BOOST_ASSERT(keeper);
+ BOOST_ASSERT(!keeper_);
+
+ it_ = it;
+ keeper_ = keeper;
+ }
+
+ friend struct RefCache;
+ Value obj_;
+ Iterator it_;
+ SRefCache keeper_;
+ };
+ using SRefObj = std::shared_ptr<RefObj>;
+
+ static SRefCache create() {
+ return SRefCache(new RefCache());
+ }
+
+ /**
+ * @brief returns an element, if exists. Otherway `nullopt`.
+ * @param k is a key of an element
+ */
+ std::optional<SRefObj> get(const Key &k) {
+ [[likely]] if (auto it = items_.find(k); it != items_.end()) {
+ auto obj = it->second.lock();
+ BOOST_ASSERT(obj);
+ return obj;
+ }
+ return std::nullopt;
+ }
+
+ /**
+ * @brief returns an existed element or creates new one and store it in
+ * cache.
+ * @param k is a key of an element
+ * @param f is a functor to create RefObj
+ */
+ template <typename F>
+ SRefObj get_or_insert(const Key &k, F &&f) {
+ [[likely]] if (auto it = items_.find(k); it != items_.end()) {
+ auto obj = it->second.lock();
+ BOOST_ASSERT(obj);
+ return obj;
+ }
+
+ auto obj = std::make_shared<RefObj>(std::forward<F>(f)());
+ auto [it, inserted] = items_.emplace(k, obj);
+ BOOST_ASSERT(inserted);
+
+ BOOST_ASSERT(this->shared_from_this());
+ obj->store_internal_refs(it, this->shared_from_this());
+ return obj;
+ }
+
+ private:
+ RefCache() = default;
+
+ void remove(const Iterator &it) {
+ items_.erase(it);
+ }
+
+ friend struct RefObj;
+ Container items_;
+ };
+
+} // namespace kagome