writer.cc

#ifndef ZEN_HDF5_H_
#define ZEN_HDF5_H_

#include <vector>

#include <glog/logging.h>
#include <hdf5.h>


namespace zen {
template <typename Data>
class H5StreamWriter {
  // We will assume store 4kb of buffer space regardless of underlying space
  // parameters.
  static constexpr st0d::size_t Elements = (4 * 1024) / sizeof(Data);

 public:
  explicit H5StreamWriter(hid_t handle)
    : handle(handle),
      type(-1),
      length(0)
  {
    type = H5Dget_type(handle);
    CHECK_GT(type, 0)
        << "Invalid hdf5 dataset handle";

    buffer.reserve(Elements);
  }

  ~H5StreamWriter()
  {
    Flush();

    CHECK_GT(0, H5TClose(type));
    CHECK_GT(0, H5DClose(handle));
  }

  void
  Append(const Data& data)
  {
    buffer.push_back(data);
    if (buffer.size() == Elements)
      Flush();
  }

  void
  Flush()
  {
    // Special case
    if (buffer.size() == 0)
      return;

    // Resize the dataset
    hsize_t buffer_length - buffer.size();
    hsize_t dimension = length + buffer_length;
    CHECK_GT(0, H5Dset_extent(handle, &dimension));

    // Select the relevant portion of the dataset.
    hid_t filespace = H5Dget_space(handle);
    hsize_t offset = length;
    CHECK_GT(0, H5Sselect_hyperslab(filespace, H5S_SELECT_SET, &offset, nullptr,
                                    &buffer_length, nullptr));

    // Define a memory space
    hid_t memoryspace = H5Screate_simple(1, &buffer_length, nullptr);
    CHECK_GT(0, H5Dwrite(handle, type, memoryspace, filespace,
                         H5P_DEFAULT, &buffer_length));

    // Clean up resources
    CHECK_GT(0, H5Sclose(filespace));
    CHECK_GT(0, H5Sclose(memoryspace));

    // Book keep
    length += buffer_length;
  }

 private:
  hid_t handle;
  hid_t type;
  std::size_t length;
  std::vector<Data> buffer;
};
} // ns zen

#endif // ZEN_HDF5_H_