OpenSpace/modules/globebrowsing/src/lrucache.inl

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 * OpenSpace                                                                             *
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#include <ghoul/misc/assert.h>
#include <ghoul/misc/profiling.h>

namespace openspace::globebrowsing::cache {

template<typename KeyType, typename ValueType, typename HasherType>
LRUCache<KeyType, ValueType, HasherType>::LRUCache(size_t size)
    : _maximumCacheSize(size)
{}

template<typename KeyType, typename ValueType, typename HasherType>
void LRUCache<KeyType, ValueType, HasherType>::clear() {
    _itemList.clear();
    _itemMap.clear();
}

template<typename KeyType, typename ValueType, typename HasherType>
void LRUCache<KeyType, ValueType, HasherType>::put(KeyType key, ValueType value) {
    putWithoutCleaning(std::move(key), std::move(value));
    clean();
}

template<typename KeyType, typename ValueType, typename HasherType>
std::vector<std::pair<KeyType, ValueType>>
LRUCache<KeyType, ValueType, HasherType>::putAndFetchPopped(KeyType key, ValueType value)
{
    putWithoutCleaning(std::move(key), std::move(value));
    return cleanAndFetchPopped();
}

template<typename KeyType, typename ValueType, typename HasherType>
bool LRUCache<KeyType, ValueType, HasherType>::exist(const KeyType& key) const {
    return (_itemMap.count(key) > 0);
}

template<typename KeyType, typename ValueType, typename HasherType>
bool LRUCache<KeyType, ValueType, HasherType>::touch(const KeyType& key) {
    ZoneScoped

    const auto it = _itemMap.find(key);
    if (it != _itemMap.end()) {
        // @TODO (abock, 2020-08-14) Instead of removing the iterator from the previous
        // position and then readding it at the front, it might make more sense to move
        // them around?  That would prevent the dynamic memoray allocation that is
        // happening here

        // Found in cache
        ValueType value = it->second->second;
        // Remove from current position
        _itemList.erase(it->second);
        _itemMap.erase(it);
        // Bump to front
        _itemList.emplace_front(key, value);
        _itemMap.emplace(key, _itemList.begin());

        return true;
    }
    else {
        return false;
    }
}

template<typename KeyType, typename ValueType, typename HasherType>
bool LRUCache<KeyType, ValueType, HasherType>::isEmpty() const {
    return (_itemMap.size() == 0);
}

template<typename KeyType, typename ValueType, typename HasherType>
ValueType LRUCache<KeyType, ValueType, HasherType>::get(const KeyType& key) {
    const auto it = _itemMap.find(key);
    // Move list iterator pointing to value
    _itemList.splice(_itemList.begin(), _itemList, it->second);
    ValueType res = it->second->second;
    return res;
}

template<typename KeyType, typename ValueType, typename HasherType>
std::pair<KeyType, ValueType> LRUCache<KeyType, ValueType, HasherType>::popMRU() {
    ghoul_assert(!_itemList.empty(), "Cannot pop LRU cache. Ensure cache is not empty");

    auto first_it = _itemList.begin();
    _itemMap.erase(first_it->first);
    std::pair<KeyType, ValueType> toReturn = _itemList.front();
    _itemList.pop_front();
    return toReturn;
}

template<typename KeyType, typename ValueType, typename HasherType>
std::pair<KeyType, ValueType> LRUCache<KeyType, ValueType, HasherType>::popLRU() {
    ghoul_assert(!_itemList.empty(), "Cannot pop LRU cache. Ensure cache is not empty");

    auto lastIt = _itemList.end();
    lastIt--;
    _itemMap.erase(lastIt->first);
    std::pair<KeyType, ValueType> toReturn = _itemList.back();
    _itemList.pop_back();
    return toReturn;
}

template<typename KeyType, typename ValueType, typename HasherType>
size_t LRUCache<KeyType, ValueType, HasherType>::size() const {
    return _itemMap.size();
}

template<typename KeyType, typename ValueType, typename HasherType>
size_t LRUCache<KeyType, ValueType, HasherType>::maximumCacheSize() const {
    return _maximumCacheSize;
}

template<typename KeyType, typename ValueType, typename HasherType>
void LRUCache<KeyType, ValueType, HasherType>::putWithoutCleaning(KeyType key,
                                                                  ValueType value)
{
    const auto it = _itemMap.find(key);
    if (it != _itemMap.end()) {
        _itemList.erase(it->second);
        _itemMap.erase(it);
    }
    _itemList.emplace_front(key, std::move(value));
    _itemMap.emplace(std::move(key), _itemList.begin());
}

template<typename KeyType, typename ValueType, typename HasherType>
void LRUCache<KeyType, ValueType, HasherType>::clean() {
    while (_itemMap.size() > _maximumCacheSize) {
        auto lastIt = _itemList.end();
        lastIt--;
        _itemMap.erase(lastIt->first);
        _itemList.pop_back();
    }
}

template<typename KeyType, typename ValueType, typename HasherType>
std::vector<std::pair<KeyType, ValueType>>
LRUCache<KeyType, ValueType, HasherType>::cleanAndFetchPopped()
{
    std::vector<std::pair<KeyType, ValueType>> toReturn;
    while (_itemMap.size() > _maximumCacheSize) {
        auto lastIt = _itemList.end();
        lastIt--;
        _itemMap.erase(lastIt->first);
        toReturn.push_back(_itemList.back());
        _itemList.pop_back();
    }
    return toReturn;
}

} // namespace openspace::globebrowsing::cache