bool load()

in src/annoylib.h [1167:1222]

• 51 lines of code
• 12 McCabe index (conditional complexity)

  bool load(const char* filename, bool prefault=false, char** error=NULL) {
#ifndef _MSC_VER
    _fd = open(filename, O_RDONLY, (int)0400);
#else
    _fd = _open(filename, _O_RDONLY, (int)0400);
#endif
    if (_fd == -1) {
      set_error_from_errno(error, "Unable to open");
      _fd = 0;
      return false;
    }
    off_t size = lseek_getsize(_fd);
    if (size == -1) {
      set_error_from_errno(error, "Unable to get size");
      return false;
    } else if (size == 0) {
      set_error_from_errno(error, "Size of file is zero");
      return false;
    } else if (size % _s) {
      // Something is fishy with this index!
      set_error_from_errno(error, "Index size is not a multiple of vector size. Ensure you are opening using the same metric you used to create the index.");
      return false;
    }

    int flags = MAP_SHARED;
    if (prefault) {
#ifdef MAP_POPULATE
      flags |= MAP_POPULATE;
#else
      annoylib_showUpdate("prefault is set to true, but MAP_POPULATE is not defined on this platform");
#endif
    }
    _nodes = (Node*)mmap(0, size, PROT_READ, flags, _fd, 0);
    _n_nodes = (S)(size / _s);

    // Find the roots by scanning the end of the file and taking the nodes with most descendants
    _roots.clear();
    S m = -1;
    for (S i = _n_nodes - 1; i >= 0; i--) {
      S k = _get(i)->n_descendants;
      if (m == -1 || k == m) {
        _roots.push_back(i);
        m = k;
      } else {
        break;
      }
    }
    // hacky fix: since the last root precedes the copy of all roots, delete it
    if (_roots.size() > 1 && _get(_roots.front())->children[0] == _get(_roots.back())->children[0])
      _roots.pop_back();
    _loaded = true;
    _built = true;
    _n_items = m;
    if (_verbose) annoylib_showUpdate("found %zu roots with degree %d\n", _roots.size(), m);
    return true;
  }