What can be improved in the following code?

Question

Dart

I need to get rid of the situation when several queries to the database arrived at once with a short period of time.
If the request has already been executed, then you need to return it from the cache.
I have implemented the following logic:

class QueryResultCache {
  List<RequestCacheStruct> requestsCacheList = [];
  // Если один и тот же запрос отправлен два раза подряд, то второй точно такой же выполнять нет смысла
  Map<int, Future<PostgreSQLResult>> pendingFutures = {}; 


Future<void> addResultToCache(sqlQuery) async {
    if(!pendingFutures.containsKey(sqlQuery.hashCode)) {
      pendingFutures.addAll({sqlQuery.hashCode: connection.query(sqlQuery, timeoutInSeconds: 3600)});
      print('Query was added to Cache');
    }
    else {
      print('This query is already running');
    }
    var queryResult = await pendingFutures[sqlQuery.hashCode]; // выполняем отложенную Future 
    await pendingFutures.remove(sqlQuery.hashCode); // удаляем обработанную Future из списка

    var queryObj = RequestCacheStruct(sqlQuery.hashCode, DateTime.now(), queryResult! );
    requestsCacheList.add(queryObj);
  }
}

The problem is that it seems to me that the logic is not quite correct (correct if I'm wrong):

- 1st call starts the request and waits.
- 2nd call just starts waiting.
- the request ends.
- 1st call "wakes up" and starts clearing pendingFutures and adding the result to the cache.
- 2nd call "wakes up" and starts clearing pendingFutures and adding the result to the cache.

Right? If yes, how to fix it?