Method empty

include/csound_threaded.hpp:77–81

        condition_variable_.notify_one();
    }
    bool empty() const
    {
        std::unique_lock<std::mutex> lock(mutex_);
        return queue_.empty();
    }
    bool try_pop(Data& popped_value)
    {
        std::unique_lock<std::mutex> lock(mutex_);