Method Resize

cpp/src/arrow/io/file.cc:476–520

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

  // Resize the mmap and file to the specified size.
  // Resize on memory mapped file region is not supported.
  Status Resize(const int64_t new_size) {
    if (!writable()) {
      return Status::IOError("Cannot resize a readonly memory map");
    }
    if (map_len_ != file_size_) {
      return Status::IOError("Cannot resize a partial memory map");
    }
    if (region_.use_count() > 1) {
      // There are buffer exports currently, the MemoryMapRemap() call
      // would make the buffers invalid
      return Status::IOError("Cannot resize memory map while there are active readers");
    }

    if (new_size == 0) {
      if (map_len_ > 0) {
        // Just unmap the mmap and truncate the file to 0 size
        region_.reset();
        RETURN_NOT_OK(::arrow::internal::FileTruncate(file_->fd(), 0));
        map_len_ = offset_ = file_size_ = 0;
      }
      position_ = 0;
      return Status::OK();
    }

    if (map_len_ > 0) {
      void* result;
      auto data = region_->data();
      RETURN_NOT_OK(::arrow::internal::MemoryMapRemap(data, map_len_, new_size,
                                                      file_->fd(), &result));
      region_->Detach();  // avoid munmap() on destruction
      region_ = std::make_shared<Region>(shared_from_this(),
                                         static_cast<uint8_t*>(result), new_size);
      map_len_ = file_size_ = new_size;
      offset_ = 0;
      if (position_ > map_len_) {
        position_ = map_len_;
      }
    } else {
      DCHECK_EQ(position_, 0);
      // the mmap is not yet initialized, resize the underlying
      // file, since it might have been 0-sized
      RETURN_NOT_OK(InitMMap(new_size, /*resize_file*/ true));
    }
    return Status::OK();
  }

  Status Seek(int64_t position) {
    if (position < 0) {