Use NexusHDF5Descriptor for HDF5 file loaders

[robertapplin]

Description:
The NexusHDF5Descriptor class has been written for use when loading files of HDF5 format. This class is much quicker to instantiate than the NexusDescriptor class, which can be used for loading either HDF4 or HDF5 files. NexusDescriptor does a walk of the entire file, whereas NexusHDF5Descriptor only reads the top-level groups in the nexus files. Often, reading the top-level groups is enough to perform a confidence check for which Load algorithm should be used.

We therefore want to use the NexusHDF5Descriptor for all Load algorithms which are ONLY used to load HDF5 nexus files (and NOT HDF4!).

The NexusHDF5Descriptor class improves the speed of the Algorithm search process by approximately a factor of 80 for the Load algorithm being searched for. The brown block is the time taken to find the LoadNexusProcessed2 algorithm when using the NexusHDF5Descriptor class. The black block is the time taken to find the LoadNexusProcessed2 algorithm when using the NexusDescriptor class.

Algorithms which can use NexusHDF5Descriptor

• LoadNexusProcessed2
• LoadNexusProcessed
• More to be found