Present/Contributors: Ben Morgan, Serhan Mete, Andre Sailer, Attila Krasznahorkay, Charles Leggett, Frank Winklmeier, Graeme Stewart, Henry Schreiner, Jim Pivarski, Matti Kortelainen, Tao Lin, Chris Green, Brett, Liz Sexton-Kennedy, James Amundson
- As always, ideas or requests for presentations/topical meetings welcome! Just contact Ben, Serhan and Martin.
- Likely have updates/tutorials on some packaging tools in next month or two (will discuss offline/through mailing list)
- Please note upcoming HSF/WLCG Virtual Workshop, 19-24 November
An Introduction to Modern CMake (Henry)
- One main take-home: links on the front page to blog and training links
- Talk is interactive, so can follow along, or revisit using the link on the agenda
- Based on CMake 3.18
- Example on Rake
- Knows what to run, but less …
- CMake = Build system generator
- But can use it to trigger build/install
- Core concepts
- minimal script
- separation of build/source dirs
- Wide range of buildsystems for C/C++
- CMake, Scons, Meson, Bazel
- Other languages have their own (e.g. Rust)
- CMake has become a standard tool
- Wide IDE support (either in CMake, or via IDEs themselves)
- Libraries provide support for integration
- Custom buildsystems going away
- e.g Qt6, Boost
- Google dual support Bazel, CMake
- Growing support/improvements in things like Thrust/TBB/PyBind11
- Attila: Isn’t TBB still using plain Make? Henry: main thing is that TBB installs a “TBBConfig.cmake” file that allows easy use of TBB in CMake projects.
- “Modern” CMake roughly from 2014 with CMake 3.0
- “Target” based
- CMake 3.12 “more modern CMake”, unified target behaviour
- CMake backward compatibility with policies
- CMake 3.12 introduced version ranges for this
- Do/Don’t recommendation
- Chris: Also minimum version determined by needs for commands (e.g. subcommands in list)
- Henry: yes, key thing is the “Do” on testing with lowest version you want to support
- Example of a bad policy in CMake 3.9:
- Thus the recommendation on don’t setting the min version low without a range
- Attila: big problem is updating min version through a project’s file
- Henry: one recommendation here (though CMake didn’t do this themselves) is not to set minimum required on anything other than
- Minimum versions by OS (e.g. “out-the-box” on CentOS etc), vs CMake features (what it can do)
- Installing CMake now very easy across all platforms (inc. GitLab/Hub CI)
- See the installing page on the website
- Modern CMake has better CLI, so can run underlying configure/build/test/install directly through the
- Key CMake convention: property initialization
- A property
MY_PROPERTY initialized by
- Key tips for packaging:
- Use targets
- Don’t write a “FindMyPackage”, write “MyPackageConfig”
- Don’t hardcode system/compiler/flags in targets
- Downloading dependencies
- classic: ExternalProject (build time)
- new: FetchContent, (configure time)
- Like submodules, much easier integration, direct use of targets provided by subproject.
- Can also integrate with Conan/Conan.io C/C++ package manager
- requires conan (but can bootstrap it in your CMake script)
- Imported targets
- A target that comes from outside the project
- Cmake 3.11 now makes these much easier to define much like all other targets
- CUDA a first class language from 3.8/9, more development since then, including
- C++ standards
- .cu files automatically handled with nvcc
- Attila: should things like CMAKE_CXX/CUDA_STANDARD be cached (so can override)?
- Henry: yes, and also consider using compile features
- Chris: Is it possible to have a subproject that uses a language that the top level project doesn’t?
- Henry: it should be, but would need to check
- Chris: have had this fail up to 3.14
- To be checked!
- Major updates to CUDA support in 3.17/18
- architectures, clang, shared cudart, FindCUDAToolkit
- Extra tools and integrations
- clang-tidy, clang tooling
- Work well with GitHub Actions (and ci)
- Also a
cmake-format tool now
- Just like black/clang-format for CMake
- Builtin GitHub Action support
- Use try_compile/try_run/WriteCompilerDetectionHeader to check/addpt to different compilers
- Python and CMake
- New “FindPython” module is recommended over separate Interp/Libs modules
- Best since 3.15, PyPy needs 3.18
- Attila: Quite slow in ATLAS due to number of calls
- Henry: due to behaviour of FindPython in supporting multiple versions, so trying to refind Python each call. Is a variable (
Python_ARTIFACTS_INTERACTIVE) that can be set to
ON/TRUE to disable that. Looks like this is new in CMake 3.18 in FindPython. Can vendor that version of the module in projects if you can’t require 3.18.
- Python/CMake: See Scikit-build and CMake wheels
- Contributions to the HSF training and CLI repo welcome!
- Chris: Is there any support for symbol visibility?
- Henry: there are target properties to set the default visibility
- Attila: there is a module for this? Yes, GenerateExportHeader!
- Liz: With modern CMake, has the overlap between build/package managers increased?
- Henry: still a role for downloading binaries with a package manager, though there’s good integration with Conan
- Attila: still think there’s a role for a higher level tools, e.g. for hardware level optimization
- Patrick: there is good communication between spack and CMake to make them work well together
- Chris: Upgrades to CETmodules are integrating the modern features, with spack.
- Graeme: EP-SFT at CERN working on turnkey stack using spack