Class mmap_array

less_slow.cpp:6966–7002

 */
template <typename type_>
class mmap_array {
    type_ *data_ = nullptr;
    std::size_t size_ = 0;

  public:
    mmap_array(std::size_t count) : size_(count) {
        // The basic mmap call, creating an anonymous region:
        void *addr = ::mmap(            //
            nullptr,                    // no specific address
            size_ * sizeof(type_),      // length in bytes
            PROT_READ | PROT_WRITE,     // read/write allowed
            MAP_SHARED | MAP_ANONYMOUS, // not backed by a file
            -1,                         // no file descriptor
            0                           // offset
        );
        if (addr == MAP_FAILED) throw std::bad_alloc();

        // Ensure the pages are locked in memory:
        if (mlock(addr, size_ * sizeof(type_)) != 0) {
            ::munmap(addr, size_ * sizeof(type_));
            throw std::runtime_error("`mlock` failed");
        }

        data_ = static_cast<type_ *>(addr);
    }

    ~mmap_array() noexcept {
        ::munlock(data_, size_ * sizeof(type_));
        ::munmap(data_, size_ * sizeof(type_));
    }

    type_ *begin() const noexcept { return data_; }
    type_ *end() const noexcept { return data_ + size_; }
    type_ &operator[](std::size_t idx) noexcept { return data_[idx]; }
    type_ operator[](std::size_t idx) const noexcept { return data_[idx]; }
    std::size_t size() const noexcept { return size_; }
};

/**
 *  @brief  Wraps the `rpc_buffer_t` with metadata about the client address.