Method GetOrInsert

cpp/src/arrow/util/concurrent_map.h:37–45

  template <typename ValueFunc>
  V GetOrInsert(const K& key, ValueFunc&& compute_value_func) {
    auto lock = mutex_.Lock();
    auto it = map_.find(key);
    if (it == map_.end()) {
      auto pair = map_.emplace(key, compute_value_func());
      it = pair.first;
    }
    return it->second;
  }

  void Erase(const K& key) {
    auto lock = mutex_.Lock();