I highly recommend Florent's suggestion. We use ccache on our CI system and for local development. We've stopped worrying about how long builds take now, since only files that are changed or that rely on things that changed contribute any meaningful amount to the build time. It also works for Make, Ninja and Xcode, so it's more flexible than relying on some feature of Make and it is also pretty easy to set up. You can set it up system wide, or you can take the approach discussed in this article <https://crascit.com/2016/04/09/using-ccache-with-cmake/> for systems where you don't have access to set up ccache globally.
On Tue, May 23, 2017 at 4:54 AM, Florent Castelli < florent.caste...@gmail.com> wrote: > > On 22 May 2017, at 20:07, Robert Patterson via cmake-developers < > cmake-developers@cmake.org> wrote: > > We understand that CMake and make already can rebuild targets which depend > on changed files, and this behavior works exactly as expected for us. Our > issue is not that make is rebuilding targets that it shouldn't. We would > like this 'compile targets which changed' behavior to work from a clean > state, not just for subsequent rebuilds. That is, from the first time cmake > / make is invoked, only the targets that depend on the given set of files > will be built, and no more. > > When a developer submits a changeset to our continuous integration tool, a > fresh copy of the repository is checked out by the worker at the commit of > the changeset. We can access the set of changed files from the commit data. > Currently, cmake and make correctly identify that the system is in a clean > state and that everything should be built if the current top-level target > is specified. This is the point where we would like our behavior to differ. > We want the rebuild changed targets behavior as if everything were already > built, but from this clean state. > > Once we have determined the targets to build, we could simply specify > these targets as goals to make in the command line, but we are hampered by > the following limitation of make. > > We are using GNU make 3.82. Invoking 'make -j target1 target2 target3' on > the command line specifies the targets as goals to make. If several goals > are specified, 'make' processes each of them in turn, in the order you name > them. https://www.gnu.org/software/make/manual/html_node/Goals.html > > Ninja does not currently work for our project. > > > It would be interesting to fix Ninja for your project then. Do you know > what isn’t currently working? > Also, Ninja has some APIs to expose all the dependency graph, which you > could probably query somehow to find out which target you need to rebuild. > > Another possibility, albeit a bit different, could be to use a compilation > cache to just rebuild everything but much faster, to the point that it > might not be relevant anymore. > > /Florent > > > On May 19, 2017, at 2:32 AM, Simon Richter <simon.rich...@hogyros.de> > wrote: > > Hi, > > On 18.05.2017 23:48, Robert Patterson via cmake-developers wrote: > > My company has a large, predominately C++ codebase, with hundreds of > targets, both for product and unit tests. In an effort to improve the > compile and test time for developers, which utilizes a continuous > integration infrastructure, it is desirable to compile only the targets > that are affected by developer's change sets. > > > Erm, it should already work this way. If Make rebuilds a target that it > shouldn't, the first step would be investigating why it thinks the > target needs to be rebuilt. > > Dependency tracking is one of the oldest problems, and cmake should use > an appropriate solution for the actual build system you use. The > approach used for Make is a bit more conservative than you would require > for GNU Make, but should nevertheless still work. > > http://make.mad-scientist.net/papers/advanced-auto-dependency-generation/ > > is a good primer on dependency list generation with Make -- CMake > generates rules that are similar to these. > > 'make' has a limitation where if 'make target1 target2 target3' is > invoked, target1, target2, and target3 are built serially, not in > parallel. > > > Which version of make are you using? > > Simon > > -- > > Powered by www.kitware.com > > Please keep messages on-topic and check the CMake FAQ at: > http://www.cmake.org/Wiki/CMake_FAQ > > Kitware offers various services to support the CMake community. For more > information on each offering, please visit: > > CMake Support: http://cmake.org/cmake/help/support.html > CMake Consulting: http://cmake.org/cmake/help/consulting.html > CMake Training Courses: http://cmake.org/cmake/help/training.html > > Visit other Kitware open-source projects at http://www.kitware.com/ > opensource/opensource.html > > Follow this link to subscribe/unsubscribe: > http://public.kitware.com/mailman/listinfo/cmake-developers > > > -- > > Powered by www.kitware.com > > Please keep messages on-topic and check the CMake FAQ at: > http://www.cmake.org/Wiki/CMake_FAQ > > Kitware offers various services to support the CMake community. For more > information on each offering, please visit: > > CMake Support: http://cmake.org/cmake/help/support.html > CMake Consulting: http://cmake.org/cmake/help/consulting.html > CMake Training Courses: http://cmake.org/cmake/help/training.html > > Visit other Kitware open-source projects at http://www.kitware.com/ > opensource/opensource.html > > Follow this link to subscribe/unsubscribe: > http://public.kitware.com/mailman/listinfo/cmake-developers > > > > -- > > Powered by www.kitware.com > > Please keep messages on-topic and check the CMake FAQ at: > http://www.cmake.org/Wiki/CMake_FAQ > > Kitware offers various services to support the CMake community. For more > information on each offering, please visit: > > CMake Support: http://cmake.org/cmake/help/support.html > CMake Consulting: http://cmake.org/cmake/help/consulting.html > CMake Training Courses: http://cmake.org/cmake/help/training.html > > Visit other Kitware open-source projects at http://www.kitware.com/ > opensource/opensource.html > > Follow this link to subscribe/unsubscribe: > http://public.kitware.com/mailman/listinfo/cmake-developers > -- Craig Scott Melbourne, Australia https://crascit.com
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