On 05/27/2015 01:33 PM, Nagy-Egri MC!tC) Ferenc via cmake-developers wrote: > like to see the NMake generator finally support multicore builds by > adding Batch Mode support to the generated makefiles.
For reference, Batch-Mode Rules are documented here: https://msdn.microsoft.com/en-us/library/f2x0zs74.aspx They support specifying multiple source files to a single "cl" invocation, as in cl -c src1.cpp src2.cpp instead of cl -c src1.cpp cl -c src2.cpp Any multi-core utilization occurs inside "cl" and NMake is not aware of it. > I have read on the CMake user mailing list, that the problem with > Batch Mode support, is that it is not trivial to implement. It is very hard to implement and may not be possible at all. See below. > * What is the design of the NMake generator in CMake? > * What is the pourpose of having so many makefiles? http://www.cmake.org/Wiki/CMake_FAQ#Why_does_CMake_generate_recursive_Makefiles.3F > * What is the reason why it is not trivial to implement batch mode? The main reasons are: * CMake generates a separate compilation line for each source in each target and the flags may differ across sources and targets. CMake does not use pattern rules for any make backend. * CMake needs to control the location of the object files and "cl" does not allow this when more than one source is given. Implementing batch mode rules would require teaching the generator to somehow recognize when a group of sources are all built with the same flags and generate a batch mode rule that matches exactly those sources and no others (likely the hardest part). This grouping would also have to account for the names that "cl" generates for the object files to avoid conflicts within a group. I do not know if generating a proper batch mode rule is possible in general. > * Where should I start browsing the source files? One place is Source/cmLocalUnixMakefileGenerator3.cxx but there is no specific spot to make a change like this. It would likely involve major refactoring. One can achieve multi-core builds without third-party tools by using the VS IDE generators. It is still possible to build from the command line with these. -Brad -- 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
