Multi Repository Build (mrb) system (2024)
Overview
Teaching: 10 min
Exercises: 0 minQuestions
How are different software versions handled?
Objectives
Understand the roles of the tool mrb
mrb
What is mrb and why do we need it?
Early on, the LArSoft team chose git and cmake as the software version manager and the build language, respectively, to keep up with industry standards and to take advantage of their new features. When we clone a git repository to a local copy and check out the code, we end up building it all. We would like LArSoft and DUNE code to be more modular, or at least the builds should reflect some of the inherent modularity of the code.
Ideally, we would like to only have to recompile a fraction of the software stack when we make a change. The granularity of the build in LArSoft and other art-based projects is the repository. So LArSoft and DUNE have divided code up into multiple repositories (DUNE ought to divide more than it has, but there are a few repositories already with different purposes). Sometimes one needs to modify code in multiple repositories at the same time for a particular project. This is where mrb comes in.
mrb stands for “multi-repository build”. mrb has features for cloning git repositories, setting up build and local products environments, building code, and checking for consistency (i.e. there are not two modules with the same name or two fcl files with the same name). mrb builds UPS products – when it installs the built code into the localProducts directory, it also makes the necessasry UPS table files and .version directories. mrb also has a tool for making a tarball of a build product for distribution to the grid. The software build example later in this tutorial exercises some of the features of mrb.
| Command | Action |
|---|---|
mrb --help |
prints list of all commands with brief descriptions |
mrb \<command\> --help |
displays help for that command |
mrb gitCheckout |
clone a repository into working area |
mrbsetenv |
set up build environment |
mrb build -jN |
builds local code with N cores |
mrb b -jN |
same as above |
mrb install -jN |
installs local code with N cores |
mrb i -jN |
same as above (this will do a build also) |
mrbslp |
set up all products in localProducts… |
mrb z |
get rid of everything in build area |
Link to the mrb reference guide
Exercise 1
There is no exercise 5. mrb example exercises will be covered in a later session as any useful exercise with mrb takes more than 30 minutes on its own. Everyone gets 100% credit for this exercise!
Key Points
The multi-repository build (mrb) tool allows code modification in multiple repositories, which is relevant for a large project like LArSoft with different cases (end user and developers) demanding consistency between the builds.