使用CMake编译时如何正确添加-pthread编译链接标志？

问题背景 #

我尝试给一个带目录和测试的CMake项目配置线程支持，参考常规方法修改了测试模块的CMakeLists.txt，但编译和链接阶段都没出现-pthread标志。

原测试模块CMakeLists.txt代码：

# Testing library
FetchContent_Declare(
  catch
  GIT_REPOSITORY "https://github.com/catchorg/Catch2.git"
  GIT_TAG v2.13.6)
FetchContent_MakeAvailable(catch)
# Adds Catch2::Catch2

# Tests need to be added as executables first
add_executable(testlib testlib.cpp)

# I'm using C++17 in the test
target_compile_features(testlib PRIVATE cxx_std_17)

# Should be linked to the main library, as well as the Catch2 testing library
target_link_libraries(testlib PRIVATE modern_library Catch2::Catch2)

# If you register a test, then ctest and make test will run it.
# You can also run examples and check the output, as well.
add_test(NAME testlibtest COMMAND testlib) # Command can be a target

我添加了线程相关配置并修改链接命令：

set(THREADS_PREFER_PTHREAD_FLAG ON)
find_package(Threads)

target_link_libraries(testlib PRIVATE modern_library Catch2::Catch2 Threads::Threads)

修改后的完整CMakeLists.txt：

# Testing library
FetchContent_Declare(
  catch
  GIT_REPOSITORY "https://github.com/catchorg/Catch2.git"
  GIT_TAG v2.13.6)
FetchContent_MakeAvailable(catch)
# Adds Catch2::Catch2

set(THREADS_PREFER_PTHREAD_FLAG ON)
find_package(Threads)


# Tests need to be added as executables first
add_executable(testlib testlib.cpp)

# I'm using C++17 in the test
target_compile_features(testlib PRIVATE cxx_std_17)

# Should be linked to the main library, as well as the Catch2 testing library
target_link_libraries(testlib PRIVATE modern_library Catch2::Catch2 Threads::Threads)

# If you register a test, then ctest and make test will run it.
# You can also run examples and check the output, as well.
add_test(NAME testlibtest COMMAND testlib) # Command can be a target

执行构建命令：

mkdir build
cmake -B. -S..
make VERBOSE

但编译输出中没有-pthread标志：

[ 88%] Building CXX object tests/CMakeFiles/testlib.dir/testlib.cpp.o
cd /home/dejovivl/test/modern-cmake/examples/extended-project/build/tests && /usr/bin/c++  -I/home/dejovivl/test/modern-cmake/examples/extended-project/src/../include -I/home/dejovivl/test/modern-cmake/examples/extended-project/build/_deps/catch-src/single_include -std=c++17 -MD -MT tests/CMakeFiles/testlib.dir/testlib.cpp.o -MF CMakeFiles/testlib.dir/testlib.cpp.o.d -o CMakeFiles/testlib.dir/testlib.cpp.o -c /home/dejovivl/test/modern-cmake/examples/extended-project/tests/testlib.cpp
[100%] Linking CXX executable testlib
cd /home/dejovivl/test/modern-cmake/examples/extended-project/build/tests && /usr/bin/cmake -E cmake_link_script CMakeFiles/testlib.dir/link.txt --verbose=1
/usr/bin/c++ CMakeFiles/testlib.dir/testlib.cpp.o -o testlib  ../src/libmodern_library.a 
make[2]: Leaving directory '/home/dejovivl/test/modern-cmake/examples/extended-project/build'
[100%] Built target testlib
make[1]: Leaving directory '/home/dejovivl/test/modern-cmake/examples/extended-project/build'
/usr/bin/cmake -E cmake_progress_start /home/dejovivl/test/modern-cmake/examples/extended-project/build/CMakeFiles 0

使用的GCC版本为11.3.0（包括aarch64交叉编译器和Ubuntu本地编译器）。

解决方案 #

方法1：强制线程库检测+显式传递编译标志 #

有时候CMake不会自动将-pthread传递到编译阶段，需要显式为目标添加编译选项，同时确保线程库被正确找到：

修改后的测试模块CMakeLists.txt：

# Testing library
FetchContent_Declare(
  catch
  GIT_REPOSITORY "https://github.com/catchorg/Catch2.git"
  GIT_TAG v2.13.6)
FetchContent_MakeAvailable(catch)
# Adds Catch2::Catch2

# 必须在find_package前设置该变量
set(THREADS_PREFER_PTHREAD_FLAG ON)
# 强制要求找到线程库，避免静默失败
find_package(Threads REQUIRED)

# Tests need to be added as executables first
add_executable(testlib testlib.cpp)

# I'm using C++17 in the test
target_compile_features(testlib PRIVATE cxx_std_17)

# 显式添加-pthread编译选项（弥补自动传递失效的情况）
if(THREADS_PREFER_PTHREAD_FLAG)
  target_compile_options(testlib PRIVATE -pthread)
endif()

# 链接线程库
target_link_libraries(testlib PRIVATE modern_library Catch2::Catch2 Threads::Threads)

# If you register a test, then ctest and make test will run it.
# You can also run examples and check the output, as well.
add_test(NAME testlibtest COMMAND testlib) # Command can be a target

方法2：手动直接指定编译和链接标志 #

如果自动配置依然失效，可以跳过CMake的线程模块，直接给目标添加标志：

# 在add_executable后添加
target_compile_options(testlib PRIVATE -pthread)
target_link_options(testlib PRIVATE -pthread)

方法3：检查根目录CMake配置 #

如果项目根目录的CMakeLists.txt设置了全局编译选项或覆盖了线程相关配置，可能会导致测试模块的设置不生效。可以尝试在根目录也添加线程配置，或者确保测试模块的配置优先级更高。

验证 #

重新执行构建命令：

rm -rf build
mkdir build
cd build
cmake -S.. -B.
make VERBOSE

此时应该能在编译和链接阶段看到-pthread标志。

内容的提问来源于stack exchange，提问作者BЈовић