using (await AsyncLock.WriterLockAsync(counterId).ConfigureAwait(false))
            {
                var entry = await _counterStore.GetAsync(counterId, cancellationToken);
                if (entry.HasValue)
                {
                    // entry has not expired
                    if (entry.Value.Timestamp + rule.PeriodTimespan.Value >= DateTime.UtcNow)
                    {
                        // increment request count
                        var totalCount = entry.Value.Count + _config.RateIncrementer?.Invoke() ?? 1;
                        // deep copy
                        counter = new RateLimitCounter
                        {
                            Timestamp = entry.Value.Timestamp,
                            Count = totalCount
                        };
                    }
                }
                // stores: id (string) - timestamp (datetime) - total_requests (long)
                await _counterStore.SetAsync(counterId, counter, rule.PeriodTimespan.Value, cancellationToken);
            }