Method Open

cpp/src/arrow/io/file.cc:452–480

  }

  Status Open(const std::string& path, FileMode::type mode, const int64_t offset = 0,
              const int64_t length = -1) {
    file_ = std::make_unique<OSFile>();

    if (mode != FileMode::READ) {
      // Memory mapping has permission failures if PROT_READ not set
      prot_flags_ = PROT_READ | PROT_WRITE;
      map_mode_ = MAP_SHARED;
      constexpr bool append = false;
      constexpr bool truncate = false;
      constexpr bool write_only = false;
      RETURN_NOT_OK(file_->OpenWritable(path, truncate, append, write_only));
    } else {
      prot_flags_ = PROT_READ;
      map_mode_ = MAP_PRIVATE;  // Changes are not to be committed back to the file
      RETURN_NOT_OK(file_->OpenReadable(path));
    }
    map_len_ = offset_ = 0;

    // Memory mapping fails when file size is 0
    // delay it until the first resize
    if (file_->size() > 0) {
      RETURN_NOT_OK(InitMMap(file_->size(), false, offset, length));
    }

    position_ = 0;

    return Status::OK();
  }

  // Resize the mmap and file to the specified size.
  // Resize on memory mapped file region is not supported.