Method front

src/common/thread_safe_queue.h:58–65

    }

    std::optional<T> front() {
        std::lock_guard<std::mutex> lock(mutex_);
        if (queue_.empty()) {
            return std::nullopt;
        }
        T t = queue_.front();
        return t;
    }

    bool full() {
        std::lock_guard<std::mutex> lock(mutex_);