// this is the class associated to a deque
class DequeEntity {
    public:
        bool remove(Elem& elem); // simple RAII methods for inserting
        void insert(Elem info);     // and removing in this deque
        size_t size() const { return q.size(); }
        bool isEmpty() { return q.empty(); }
    private:
        std::mutex m;
        std::condition_variable write, read;
        std::deque<Elem> q;
};

// this class contains the three deques
class DequeManager {
    public:
        void insert(Elem e);
        void remove(void); // <--- this is my real struggle
        void printQueues(void);
        void startRemoverThread(void); // start removerThread; called once

    private:
        std::thread removerThread;
        std::array<DequeEntity, 3> deques;
};

bool DequeEntity::remove(Elem& elem) {
    std::unique_lock<std::mutex> lck(m);
    if (read.wait_for(lck, std::chrono::milliseconds(1000),
        [this]() { return q.size() > 0; })) {
        try {
            ic = std::move(q.front());
            q.pop_front();
        } catch (const std::exception& e) {
            debug_red(e.what());
            return false;
        }
        write.notify_one();
        return true;
    }
    else {
        // timeout expired, failed to retrieve element from deque
        return false;
    }
}

void DequeManager::remove(void) {
    Elem elem;

    while (true) {
        numQueue = 0;
        for (auto &q : deques) {
            if (q.remove(elem)) {
                // do stuff with elem
                // if there's more to read, go ahead
                while (q.size() > 0) {
                    Elem elem;
                    if (q.remove(elem)) {
                        // do stuff with elem
                    } else {
                        // failed to get another element;
                        // go on next deque
                        break;
                    }
                }
            }
        }
    }
}