public class SmartMessageStore : IMessageStore
{
    private readonly IMessageStore _store = new InProcessMessageStore();

    public Task<IEnumerable<Message>> GetAll(string key)
    {
        lock (_store)
        {
            return _store.GetAll(key);
        }
    }

    public Task<IEnumerable<Message>> GetAllSince(string key, long id)
    {
        return GetLastId().ContinueWith(t =>
        {
            lock (_store)
            {
                if (t.Result.HasValue)
                {
                    if (id > t.Result.Value)
                    {
                        var recent = _store.GetAllSince(key, t.Result.Value - 1);
                        var idOffset = id - t.Result.Value - 1;
                        return recent.ContinueWith(messagesTask =>
                            messagesTask.Result.Select(m => OffsetMessageId(m, idOffset))
                        );
                    }
                }
                return _store.GetAllSince(key, id);
            }
        }).Unwrap();
    }

    Message OffsetMessageId(Message message, long idOffset)
    {
        return new Message(message.SignalKey, message.Id + idOffset, message.Value, message.Created);
    }

    public Task<long?> GetLastId()
    {
        lock (_store)
        {
            return _store.GetLastId();
        }
    }

    public Task Save(string key, object value)
    {
        lock (_store)
        {
            return _store.Save(key, value);
        }
    }
}