CMake failing to detect pthreads due to warnings

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

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

Answer 2

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).