2013/8/12 Paul Smith <[email protected]>: > On Mon, 2013-08-12 at 22:35 +0200, Eric Noulard wrote: >> 2013/8/12 Paul Smith <[email protected]>: >> > >> > So I have tried using add_custom_command() with OUTPUT, but the >> > documentation says: >> > >> > "Do not list the output in more than one independent target that may build >> > in parallel or the two instances of the rule may conflict (instead use >> > add_custom_target to drive the command and make the other targets depend on >> > that one)." >> > >> > Sure enough, it seems that if I have my different libraries depend on these >> > outputs I get problems during parallel builds. So then I tried to use >> > add_custom_target(), but that says: >> > >> > "The target has no output file and is ALWAYS CONSIDERED OUT OF DATE" >> > >> > and, sure enough, if I do it this way my source files (and everything that >> > depends on them) rebuild every time I run the build, even if nothing has >> > changed. This is a big bummer. >> >> I did never tried befoire but think you should "simply" keep your >> current add_custom_command and create a new target with >> add_custom_target whose only purpose is to "serialize" the dependency >> for the 2 (or more) independent libraries which use the output of your >> custom command concurrently. > >> add_custom_target(SerializeTarget >> DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/generated.c) >> >> add_library(MyLib1 ${CMAKE_CURRENT_BINARY_DIR}/generated.c lib1.c) >> set_target_properties(MyLib1 PROPERTIES COMPILE_FLAGS -DDEFGEN=3) >> add_dependencies(MyLib1 SerializeTarget) >> >> add_library(MyLib2 ${CMAKE_CURRENT_BINARY_DIR}/generated.c lib2.c) >> set_target_properties(MyLib2 PROPERTIES COMPILE_FLAGS -DDEFGEN=4) >> add_dependencies(MyLib2 SerializeTarget) > > OK, maybe I'm misunderstanding but if the SerializeTarget is considered > "always out of date" because it was defined with add_custom_target() > then won't that cause the two libraries to always rebuild, since > something they depend on is always out of date? Maybe I'm thinking of > it too much like make.
This is puzzling but as far as I understand it, since SerializeTarget has no output it cannot trigger the rebuilt of a target (nioether Lib1 nor Lib2), however whenever you need (or ask) to build Lib1 or Lib2 then SerializeTarget has to be executed and consequently the add_custom_command will be if the "generated.c" file is out of date. i.e. if you build Lib1 or Lib2 then SerializeTarget will be built. Building Lib1 target does not mean recompilation will occur because the "file dependency" is automatically handled by cmake using the source files arguments of the add_library call. so you may have: $ make [ 14%] Built target SerializeTarget [ 57%] Built target MyLib1 [100%] Built target MyLib2 every expected target is built (because of the target dependencies) but no compilation occurs because none is necessary. but $ rm generated.c $ make [ 14%] Generating generated.c [ 14%] Built target SerializeTarget Scanning dependencies of target MyLib1 [ 28%] Building C object CMakeFiles/MyLib1.dir/generated.c.o Linking C static library libMyLib1.a [ 57%] Built target MyLib1 Scanning dependencies of target MyLib2 [ 71%] Building C object CMakeFiles/MyLib2.dir/generated.c.o Linking C static library libMyLib2.a [100%] Built target MyLib2 works as expected, and $ touch ../lib1.c erk@ct-wdtim102h:b$ make [ 14%] Built target SerializeTarget Scanning dependencies of target MyLib1 [ 28%] Building C object CMakeFiles/MyLib1.dir/lib1.c.o Linking C static library libMyLib1.a [ 57%] Built target MyLib1 [100%] Built target MyLib2 as well. > I'll look at the stuff you've sent and try to adjust it for my > situation. It should work. -- Erk L'élection n'est pas la démocratie -- http://www.le-message.org -- 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://www.cmake.org/mailman/listinfo/cmake
