std::enable_if_t init()

in src/backend/pagemap.h [153:206]

• 38 lines of code
• 3 McCabe index (conditional complexity)

    std::enable_if_t<!has_bounds_> init()
    {
      static_assert(
        has_bounds_ == has_bounds, "Don't set SFINAE template parameter!");
      static constexpr size_t REQUIRED_SIZE = required_size();

#ifdef SNMALLOC_CHECK_CLIENT
      // Allocate a power of two extra to allow the placement of the
      // pagemap be difficult to guess.
      size_t additional_size = bits::next_pow2(REQUIRED_SIZE) * 4;
      size_t request_size = REQUIRED_SIZE + additional_size;
#else
      size_t request_size = REQUIRED_SIZE;
#endif

      auto new_body_untyped = PAL::reserve(request_size);

      if (new_body_untyped == nullptr)
      {
        PAL::error("Failed to initialise snmalloc.");
      }

#ifdef SNMALLOC_CHECK_CLIENT
      // Begin pagemap at random offset within the additionally allocated space.
      static_assert(bits::is_pow2(sizeof(T)), "Next line assumes this.");
      size_t offset = get_entropy64<PAL>() & (additional_size - sizeof(T));
      auto new_body =
        reinterpret_cast<T*>(pointer_offset(new_body_untyped, offset));

      if constexpr (pal_supports<LazyCommit, PAL>)
      {
        void* start_page = pointer_align_down<OS_PAGE_SIZE>(new_body);
        void* end_page = pointer_align_up<OS_PAGE_SIZE>(
          pointer_offset(new_body, REQUIRED_SIZE));
        // Only commit readonly memory for this range, if the platform supports
        // lazy commit.  Otherwise, this would be a lot of memory to have
        // mapped.
        PAL::notify_using_readonly(
          start_page, pointer_diff(start_page, end_page));
      }
#else
      auto new_body = reinterpret_cast<T*>(new_body_untyped);
#endif
      // Ensure bottom page is committed
      // ASSUME: new memory is zeroed.
      PAL::template notify_using<NoZero>(
        pointer_align_down<OS_PAGE_SIZE>(new_body), OS_PAGE_SIZE);

      // Set up zero page
      new_body[0] = body[0];

      body = new_body;
      body_opt = new_body;
    }