问题描述
我正在使用BUILD_IN_SOURCE = TRUE的使用ExternalProject的项目，并且每次都会重建整个项目（所有源和目标），好像make无法看到文件已经存在。我的实现如下所示：
# Need to explicitly enable ExternalProject functionality
include(ExternalProject)
# Download or update library as an external project
ExternalProject_Add(project_bdsg
GIT_REPOSITORY https://github.com/vgteam/libbdsg-easy.git
PREFIX ${CMAKE_CURRENT_BINARY_DIR}/external/
CONfigURE_COMMAND ""
UPDATE_disCONNECTED True
BUILD_ALWAYS False
BUILD_IN_SOURCE True
INSTALL_DIR ${CMAKE_SOURCE_DIR}/external/bdsg/
INSTALL_COMMAND make INSTALL_PREFIX=${CMAKE_SOURCE_DIR}/external/bdsg/ install
)
# Define INSTALL_DIR as the install directory for external library
ExternalProject_Get_Property(project_bdsg INSTALL_DIR)
# Create new library for external project (so it can be linked with main library)
add_library(bdsg STATIC IMPORTED)
set_property(TARGET bdsg
PROPERTY IMPORTED_LOCATION ${INSTALL_DIR}/lib/libbdsg.a)
add_library(divsufsort STATIC IMPORTED)
set_property(TARGET divsufsort
PROPERTY IMPORTED_LOCATION ${INSTALL_DIR}/lib/libdivsufsort64.a)
add_library(libhandlegraph STATIC IMPORTED)
set_property(TARGET libhandlegraph
PROPERTY IMPORTED_LOCATION ${INSTALL_DIR}/lib/libhandlegraph.a)
add_library(libsdsl STATIC IMPORTED)
set_property(TARGET libsdsl
PROPERTY IMPORTED_LOCATION ${INSTALL_DIR}/lib/libsdsl.a)
# Define library as dependent on the downloaded project
add_dependencies(bdsg
project_bdsg
libsdsl
libhandlegraph
divsufsort)
# Define main library as dependent on the downloaded project (transitively)
add_dependencies(Bluntifier bdsg)
# Ensure that main library has access to primary dependencies' and secondary dependencies' headers
include_directories(external/bdsg/include/)
并且我有这样定义的目标：
add_executable(${FILENAME_PREFIX} src/test/${FILENAME_PREFIX}.cpp)
set_property(TARGET ${FILENAME_PREFIX} PROPERTY INSTALL_RPATH "$ORIGIN")
target_link_libraries(${FILENAME_PREFIX}
Bluntifier
Threads::Threads
bdsg
divsufsort
libhandlegraph
libsdsl)
通过一些调试输出运行make会给我这样的消息：
Updating goal targets....
Considering target file 'CMakeFiles/Bluntifier.dir/build'.
File 'CMakeFiles/Bluntifier.dir/build' does not exist.
Considering target file 'Bluntifier.a'.
Considering target file 'CMakeFiles/Bluntifier.dir/link.txt'.
Finished prerequisites of target file 'CMakeFiles/Bluntifier.dir/link.txt'.
No need to remake target 'CMakeFiles/Bluntifier.dir/link.txt'.
Considering target file 'CMakeFiles/Bluntifier.dir/src/adjacency_components.cpp.o'.
File 'CMakeFiles/Bluntifier.dir/src/adjacency_components.cpp.o' does not exist.
Considering target file '../src/adjacency_components.cpp'.
Finished prerequisites of target file '../src/adjacency_components.cpp'.
No need to remake target '../src/adjacency_components.cpp'.
Considering target file '../external/bdsg/include/bdsg/internal/packed_structs.hpp'.
Finished prerequisites of target file '../external/bdsg/include/bdsg/internal/packed_structs.hpp'.
No need to remake target '../external/bdsg/include/bdsg/internal/packed_structs.hpp'.
Considering target file '../external/bdsg/include/handlegraph/expanding_overlay_graph.hpp'.
Finished prerequisites of target file '../external/bdsg/include/handlegraph/expanding_overlay_graph.hpp'.
No need to remake target '../external/bdsg/include/handlegraph/expanding_overlay_graph.hpp'.
Considering target file '../external/bdsg/include/handlegraph/handle_graph.hpp'.
Finished prerequisites of target file '../external/bdsg/include/handlegraph/handle_graph.hpp'.
No need to remake target '../external/bdsg/include/handlegraph/handle_graph.hpp'.
Considering target file '../external/bdsg/include/handlegraph/iteratee.hpp'.
Finished prerequisites of target file '../external/bdsg/include/handlegraph/iteratee.hpp'.
No need to remake target '../external/bdsg/include/handlegraph/iteratee.hpp'.
Considering target file '../external/bdsg/include/handlegraph/types.hpp'.
Finished prerequisites of target file '../external/bdsg/include/handlegraph/types.hpp'.
No need to remake target '../external/bdsg/include/handlegraph/types.hpp'.
Considering target file '../external/bdsg/include/handlegraph/util.hpp'.
Finished prerequisites of target file '../external/bdsg/include/handlegraph/util.hpp'.
No need to remake target '../external/bdsg/include/handlegraph/util.hpp'.
Considering target file '../external/bdsg/include/sdsl/bits.hpp'.
Finished prerequisites of target file '../external/bdsg/include/sdsl/bits.hpp'.
No need to remake target '../external/bdsg/include/sdsl/bits.hpp'.
Considering target file '../external/bdsg/include/sdsl/config.hpp'.
Finished prerequisites of target file '../external/bdsg/include/sdsl/config.hpp'.
No need to remake target '../external/bdsg/include/sdsl/config.hpp'.
Considering target file '../external/bdsg/include/sdsl/int_vector.hpp'.
Finished prerequisites of target file '../external/bdsg/include/sdsl/int_vector.hpp'.
No need to remake target '../external/bdsg/include/sdsl/int_vector.hpp'.
Considering target file '../external/bdsg/include/sdsl/int_vector_buffer.hpp'.
Finished prerequisites of target file '../external/bdsg/include/sdsl/int_vector_buffer.hpp'.
No need to remake target '../external/bdsg/include/sdsl/int_vector_buffer.hpp'.
Considering target file '../external/bdsg/include/sdsl/io.hpp'.
Finished prerequisites of target file '../external/bdsg/include/sdsl/io.hpp'.
No need to remake target '../external/bdsg/include/sdsl/io.hpp'.
Considering target file '../external/bdsg/include/sdsl/iterators.hpp'.
Finished prerequisites of target file '../external/bdsg/include/sdsl/iterators.hpp'.
No need to remake target '../external/bdsg/include/sdsl/iterators.hpp'.
Considering target file '../external/bdsg/include/sdsl/memory_management.hpp'.
Finished prerequisites of target file '../external/bdsg/include/sdsl/memory_management.hpp'.
No need to remake target '../external/bdsg/include/sdsl/memory_management.hpp'.
Considering target file '../external/bdsg/include/sdsl/ram_filebuf.hpp'.
Finished prerequisites of target file '../external/bdsg/include/sdsl/ram_filebuf.hpp'.
No need to remake target '../external/bdsg/include/sdsl/ram_filebuf.hpp'.
Considering target file '../external/bdsg/include/sdsl/ram_fs.hpp'.
Finished prerequisites of target file '../external/bdsg/include/sdsl/ram_fs.hpp'.
No need to remake target '../external/bdsg/include/sdsl/ram_fs.hpp'.
Considering target file '../external/bdsg/include/sdsl/sdsl_concepts.hpp'.
Finished prerequisites of target file '../external/bdsg/include/sdsl/sdsl_concepts.hpp'.
No need to remake target '../external/bdsg/include/sdsl/sdsl_concepts.hpp'.
Considering target file '../external/bdsg/include/sdsl/sfstream.hpp'.
Finished prerequisites of target file '../external/bdsg/include/sdsl/sfstream.hpp'.
No need to remake target '../external/bdsg/include/sdsl/sfstream.hpp'.
Considering target file '../external/bdsg/include/sdsl/structure_tree.hpp'.
Finished prerequisites of target file '../external/bdsg/include/sdsl/structure_tree.hpp'.
No need to remake target '../external/bdsg/include/sdsl/structure_tree.hpp'.
Considering target file '../external/bdsg/include/sdsl/uintx_t.hpp'.
Finished prerequisites of target file '../external/bdsg/include/sdsl/uintx_t.hpp'.
No need to remake target '../external/bdsg/include/sdsl/uintx_t.hpp'.
Considering target file '../external/bdsg/include/sdsl/util.hpp'.
Finished prerequisites of target file '../external/bdsg/include/sdsl/util.hpp'.
No need to remake target '../external/bdsg/include/sdsl/util.hpp'.
Considering target file '../inc/adjacency_components.hpp'.
Finished prerequisites of target file '../inc/adjacency_components.hpp'.
No need to remake target '../inc/adjacency_components.hpp'.
Considering target file '../inc/subtractive_graph.hpp'.
Finished prerequisites of target file '../inc/subtractive_graph.hpp'.
No need to remake target '../inc/subtractive_graph.hpp'.
Considering target file '../inc/utility.hpp'.
Finished prerequisites of target file '../inc/utility.hpp'.
No need to remake target '../inc/utility.hpp'.
Pruning file '../src/adjacency_components.cpp'.
Pruning file 'CMakeFiles/Bluntifier.dir/flags.make'.
Finished prerequisites of target file 'CMakeFiles/Bluntifier.dir/src/adjacency_components.cpp.o'.
Must remake target 'CMakeFiles/Bluntifier.dir/src/adjacency_components.cpp.o'.
[ 38%] Building CXX object CMakeFiles/Bluntifier.dir/src/adjacency_components.cpp.o
Successfully remade target file 'CMakeFiles/Bluntifier.dir/src/adjacency_components.cpp.o'.
其中adjacency_components.cpp是每次我运行make时都会重建的几个源文件之一。为什么得出结论认为需要重建这些目标？
解决方法
在我的调试输出中进一步查找之后，很明显，cmake正在从ExternalProject的下载内容中跟踪文件时间戳。由于每次我重新编译时都会重新下载，因此总会有一个新的时间戳，导致所有受抚养者相对而言过时，然后触发重新编译所有内容。要在开发过程中暂时停止此操作，只需添加以下行：
DOWNLOAD_COMMAND ""
UPDATE_COMMAND ""
到ExternalProject参数。理想情况下，这将与开发人员可以调用的标志相关联，这样就不是默认行为。