Method insert

src/mgr/MgrMapCache.cc:92–130

template<class Value>
typename LFUCache<Value>::InsertRes
LFUCache<Value>::insert(std::string_view key, Value value) {
  if (!can_write_cache(key)) {
    return InsertRes{false};
  }

  std::unique_lock<std::shared_mutex> l(m);
  // Re-check enabled after acquiring lock: state may have flipped while waiting.
  if (!enabled.load(std::memory_order_relaxed)) {
    return InsertRes{false};
  }

  auto it = cache_data.find(key);
  if (it != cache_data.end()) {
    InsertRes res{true};
    res.replaced = std::move(it->second.val);
    it->second.val = std::move(value);
    return res;
  }

  // New insert counts as a miss (cache didn't have it)
  mark_miss();

  InsertRes res{true};
  if (cache_data.size() >= capacity && !cache_data.empty()) {
    auto min_it = std::min_element(cache_data.begin(),
      cache_data.end(),
      [](const auto& a, const auto& b) {
        return a.second.hits.load(std::memory_order_relaxed) <
               b.second.hits.load(std::memory_order_relaxed);
    });
    res.evicted = std::move(min_it->second.val);
    cache_data.erase(min_it);
  }

  // Allocate std::string only here, when we actually need to store a new key.
  cache_data.emplace(std::string(key), Entry(std::move(value)));
  return res;
}

template <class Value>
MgrMapCache<Value>::MgrMapCache(uint16_t size)