CMake failing to detect pthreads due to warnings - gcc

Question

I get an error when making a project with CMake:
-- Could NOT find Threads (missing: Threads_FOUND)
The error log shows that CMake tripped up over something truly banal:
/usr/bin/cc -std=c11 -D_GNU_SOURCE -Wall -Wextra -Wpointer-arith -Wundef -Wvla -Wwrite-strings -Werror -Wno-error=extra -Wno-error=deprecated-declarations -Wno-error=sign-compare -Wno-error=strict-aliasing -Wno-error=type-limits -Wno-unused-parameter -Wno-error=unused-variable -Wno-error=undef -Wno-error=uninitialized -Wlogical-op -Wno-error=maybe-uninitialized -Waggregate-return -Wnested-externs -Wold-style-definition -Wstrict-prototypes -march=native -o CMakeFiles/cmTryCompileExec2533162744.dir/CheckIncludeFiles.c.o -c /mnt/shared/fooproj/build/release/CMakeFiles/CMakeTmp/CheckIncludeFiles.c
/mnt/shared/fooproj/build/release/CMakeFiles/CMakeTmp/CheckIncludeFiles.c:5:5:
error: function declaration isn’t a prototype [-Werror=strict-prototypes]
int main(){return 0;}
^
/mnt/shared/fooproj/build/release/CMakeFiles/CMakeTmp/CheckIncludeFiles.c:
In function ‘main’:
/mnt/shared/fooproj/build/release/CMakeFiles/CMakeTmp/CheckIncludeFiles.c:5:5:
error: old-style function definition [-Werror=old-style-definition]
cc1: all warnings being treated as errors
[...]
Source:
/* */
#include <pthread.h>
int main(){return 0;}
This really should be no reason for CMake to think Threads doesn't exist. How do I go about fixing this?

Answer 1

I believe this is CMake bug 15058 which I just reported.
The test that CMake is using to check the include file uses an old-style C function definition. If -Wold-style-definition -Werror is in effect, gcc will barf on this.
I included a patch in the bug report linked above, but for a quick fix, find the file Modules/CheckIncludeFiles.cmake in your CMake installation (possibly in /usr/share/cmake or similar), find the line
"${CMAKE_CONFIGURABLE_FILE_CONTENT}\n\nint main(){return 0;}\n")
and change int main() to int main(void).

Answer 2

Issue seems to be still there.
I try to compile the lates nominatim. seems i got the same error.
Determining if the pthread_create exist failed with the following output:
Change Dir: /home/mikelaptop/Desktop/nominatim/290102/Nominatim/build/CMakeFiles/CMakeTmp
Run Build Command:"/usr/bin/make" "cmTC_b87d8/fast"
/usr/bin/make -f CMakeFiles/cmTC_b87d8.dir/build.make CMakeFiles/cmTC_b87d8.dir/build
make[1]: Entering directory '/home/mikelaptop/Desktop/nominatim/290102/Nominatim/build/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_b87d8.dir/CheckSymbolExists.c.o
/usr/bin/cc -o CMakeFiles/cmTC_b87d8.dir/CheckSymbolExists.c.o -c /home/mikelaptop/Desktop/nominatim/290102/Nominatim/build/CMakeFiles/CMakeTmp/CheckSymbolExists.c
Linking C executable cmTC_b87d8
/usr/bin/cmake -E cmake_link_script CMakeFiles/cmTC_b87d8.dir/link.txt --verbose=1
/usr/bin/cc -rdynamic CMakeFiles/cmTC_b87d8.dir/CheckSymbolExists.c.o -o cmTC_b87d8
CMakeFiles/cmTC_b87d8.dir/CheckSymbolExists.c.o: In function `main':
CheckSymbolExists.c:(.text+0x1b): undefined reference to `pthread_create'
collect2: error: ld returned 1 exit status
CMakeFiles/cmTC_b87d8.dir/build.make:97: recipe for target 'cmTC_b87d8' failed
make[1]: *** [cmTC_b87d8] Error 1
make[1]: Leaving directory '/home/mikelaptop/Desktop/nominatim/290102/Nominatim/build/CMakeFiles/CMakeTmp'
Makefile:126: recipe for target 'cmTC_b87d8/fast' failed
make: *** [cmTC_b87d8/fast] Error 2
File /home/mikelaptop/Desktop/nominatim/290102/Nominatim/build/CMakeFiles/CMakeTmp/CheckSymbolExists.c:
/* */
#include <pthread.h>
int main(int argc, char** argv)
{
(void)argv;
#ifndef pthread_create
return ((int*)(&pthread_create))[argc];
#else
(void)argc;
return 0;
#endif
}
Determining if the function pthread_create exists in the pthreads failed with the following output:
Change Dir: /home/mikelaptop/Desktop/nominatim/290102/Nominatim/build/CMakeFiles/CMakeTmp
Run Build Command:"/usr/bin/make" "cmTC_eb9e3/fast"
/usr/bin/make -f CMakeFiles/cmTC_eb9e3.dir/build.make CMakeFiles/cmTC_eb9e3.dir/build
make[1]: Entering directory '/home/mikelaptop/Desktop/nominatim/290102/Nominatim/build/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_eb9e3.dir/CheckFunctionExists.c.o
/usr/bin/cc -DCHECK_FUNCTION_EXISTS=pthread_create -o CMakeFiles/cmTC_eb9e3.dir/CheckFunctionExists.c.o -c /usr/share/cmake-3.9/Modules/CheckFunctionExists.c
Linking C executable cmTC_eb9e3
/usr/bin/cmake -E cmake_link_script CMakeFiles/cmTC_eb9e3.dir/link.txt --verbose=1
/usr/bin/cc -DCHECK_FUNCTION_EXISTS=pthread_create -rdynamic CMakeFiles/cmTC_eb9e3.dir/CheckFunctionExists.c.o -o cmTC_eb9e3 -lpthreads
/usr/bin/ld: cannot find -lpthreads
collect2: error: ld returned 1 exit status
CMakeFiles/cmTC_eb9e3.dir/build.make:97: recipe for target 'cmTC_eb9e3' failed
make[1]: *** [cmTC_eb9e3] Error 1
make[1]: Leaving directory '/home/mikelaptop/Desktop/nominatim/290102/Nominatim/build/CMakeFiles/CMakeTmp'
Makefile:126: recipe for target 'cmTC_eb9e3/fast' failed
make: *** [cmTC_eb9e3/fast] Error 2
Edit: cmake -lpthread .. seems to fix this