Implementation of an HDF5 IO layer for PODIO

Google Summer of Code 2019 Evaluation Test

If you are interested in our GSoC project to implement an HDF5 layer in the High-Energy Physics event model software PODIO, then please complete the following evaluation test.

This exercise can be completed on most modern Linux distributions, such as Ubuntu18.04, CentOS7, Fedora29. OS X is possible, but more tricky to setup, so we do not recommend it. It is not possible to use Windows.

Docker Container

If you do not have direct access to a suitable platform we provide a Docker container that you can use to complete the exercise, graemeastewart/u18-podio.

(It is not necessary to have root access in the container, but if you need it you can use sudo and the password is hsf.)

Startup Instructions

1. Clone a local copy of the PODIO repository from GitHub.

2. Install a local copy of the HEP ROOT software

   • We recommend using the latest stable version of ROOT (6.16.00).
   • Downloading a pre-built version of ROOT is perfectly acceptable.
   • N.B. In the graemeastewart/u18-podio container this is provided for you, installed into /opt.

3. Compile PODIO and run its unit tests, to check that your development setup is working.

   • Follow the instructions on the PODIO github.
   • Finally, make test should run and successfully complete the five PODIO unit tests.

N.B. If you are having trouble with any dependencies in your environment you can consult the Dockerfiles of the container we provided and that might help you solve the issue: 1 and 2.

Evaluation Test

1. Write a shell script that will checkout the PODIO code, compile it and run the unit tests.

2. Study the PODIO sample data model in tests/datalayout.yaml.

3. Look at the data object SimpleStruct, and make sure you understand how the data is represented as a C++ object.

   • The code in tests/src and tests/datamodel will help.

4. Write a code example in C++ that will use the HDF5 libraries to

   • Create a SimpleStruct array, of size 100, in memory and write some predictable data into it.
   • Create a compound HDF5 datatype that corresponds to the SimpleStruct.
   • Write the SimpleStruct data into an HDF5 file.
   • N.B. it's not necessary to use the PODIO C++ code for this, but you can if you want.

5. Write a second piece of code in C++ that will reread the HDF5 file and check that the SimpleStruct array is successfully deserialised into memory.

6. Your code should at least compile using make; using cmake is also fine.

Submitting Your Answer

You can submit your answer by sending the mentors a link to a github repository with the solution.

• Make sure you include:
  • The shell script that will checkout PODIO, comple and test it.
  • The C++ to write and read back SimpleStucts in HDF5 format.
  • A README.md that describes how to compile and run your solution.

It is advisable that you test that your solution works properly in the graemeastewart/u18-podio container - this is what we will use for testing the solutions.

If you need clarification on any aspect of the test then you are very welcome to contact the mentors:

• Graeme Stewart graeme.andrew.stewart@cern.ch
• Benedikt Hegner bhegner@bnl.gov
• Frank Gaede frank.gaede@desy.de