SimGrid  3.19.1
Versatile Simulation of Distributed Systems
Coding Standard and Technical Considerations

There is two main things you want to know about the internals of SimGrid. First, you need to understand the component organization, as SimGrid is heavily layered, with each level being rather highly specialized and optimized toward a task. For that, please head to Project Architecture Overview.

Then, if you work actively on the SimGrid project, the second point you need to understand is about the infrastructure of the SimGrid project, ie how to extend the framework in any way, how the automatic tests are run, and so on. These informations are split on several pages, as follows:

Insider's Configuration

The default build configuration of SimGrid fits the user needs, but they are not adapted to the ones actually working on SimGrid. See Build Configuration for more information. Note that this is very different from runtime configuration.

In particular, the build is configured by default to produce highly optimized binaries, at the price of high compilation time. The rationale is that users will compile SimGrid only once, and use it many times. This is exactly the contrary for the insiders, so you want to turn off enable_compile_optimizations.

Symmetrically, enable_compile_warnings is off for the users because we don't want to bother them with compiler warnings (that abort the build in SimGrid), but any insider must turn this option on, or your code will be refused from the main repository.

Automatically Enforcing our Coding Standards

If you plan to commit code to the SimGrid project, you definitely need to install the relevant tool to ensure that your changes follow our coding standards:

# install clang-format
sudo apt-get install clang-format-3.8 # debian

# tell git to call the script on each commit
ln -s $(realpath tools/git-hooks/clang-format.pre-commit) .git/hooks/pre-commit

This will add an extra verification before integrating any commit that you could prepare. If your code does not respects our formating code, git will say so, and provide a ready to use patch that you can apply to improve your commit. Just carefully read the error message you get to find the exact command with git-apply to fix your formating.

If you find that for a specific commit, the formatter does a very bad job, then add –no-verify to your git commit command line.

Insider tricks

Over the years, we accumulated a few tricks that make it easier to work with SimGrid. Here is a somewhat unsorted list of such tricks.

Easy testing

Launching all tests can be very time consuming, so you want to build and run the tests in parallel. Also, you want to save the build output to disk, for further reference. This is exactly what the script does. It is upper-cased so that the shell completion works and allow to run it in 4 key press: ./B<tab>

Note that if you build out of tree (as you should, see below), the script builds the build/default directory. I usually copy the file in each build/ subdir to test each of them separately.

Easy out of tree builds

It is easy to break one build configuration or another. That's perfectly OK and we will not point fingers if it happens. But it is somewhat forbidden to leave the tree broken for a long while. Monitor the build daemons after you push something, and strive to fix any breakage ASAP.

To easily switch between the configs without rebuilding everything, create a set of out of tree builds (as explained in Out of Tree Compilation) in addition to your main build tree. To not mess with git, you want to put your build tree under the build/ directory, which is ignored by git. For example, I have the following directories: build/clang build/java build/full (but YMMV).

Then, the problem is that when you traverse these directories, you cannot edit the sources (that are in the srcdir, while you're in bindir). This makes it difficult to launch the tests and everything.

To solve that issue, just call make hardlinks from your build dir. This will create hard links allowing to share every source files into the build dir. They are not copied, but hard linked. It means that each file is accessible under several names, from the srcdir and from the bindirs. If you edit a source file found under bindir, the srcdir version (visible to git) will also be changed (that's the same file, after all).

Note that the links sometimes broken by git or others. Relaunching make hardlinks may help if you're getting incoherent build results.