What is the proper use of CMake FindThreads with modern C++?

Question

The source for the CMake (https://github.com/Kitware/CMake/blob/master/Modules/FindThreads.cmake) claims the following about the "FindThreads" functionality:

This module is not needed for C++11 and later if threading is done using std::thread from the standard library.

But if I follow this advice (on my Mint18 x86_64 system, gcc8, CMake 3.13.2) I get:

/usr/bin/ld: CMakeFiles/prism-esm-dummy.dir/src/main.cpp.o: undefined reference to symbol 'pthread_create@@GLIBC_2.2.5'
//lib/x86_64-linux-gnu/libpthread.so.0: error adding symbols: DSO missing from command line
collect2: error: ld returned 1 exit status

If the module is exercised (as best I could figure using other SO articles and previously given advice):

set (THREADS_PREFER_PTHREAD_FLAG ON)
find_package (Threads REQUIRED)

add_executable(my_app main.cpp)
target_link_libraries (my_app Threads::Threads)

... the result is the same.

THREADS_FOUND is true and CMAKE_USE_PTHREADS_INIT is 1, but i get no -pthread under compile, or a -lpthread during link. I checked a number of other variables mentioned in the module, and all I tried were not set.

Is there a correct way to do this? Or should I just use the normal flags and move on with my life?

Are you using `pthread_*` APIs directly in your code? – arrowd Jan 15 '19 at 04:14 — arrowd, Jan 15 '19 at 04:14
No. I'm using std::thread. – Rich Henry Jan 15 '19 at 13:54 — Rich Henry, Jan 15 '19 at 13:54

score 5 · Answer 1 · answered Mar 05 '20 at 03:18

5

find_package( Threads )
target_link_libraries( ${PROJECT_NAME} ${CMAKE_THREAD_LIBS_INIT} )

see also https://stackoverflow.com/a/5402608/10838321

answered Mar 05 '20 at 03:18

Worked perfectly. This save me a lot of time. Thanks a ton! – Malloc Mar 21 '22 at 04:49

score 0 · Answer 2 · answered May 05 '22 at 11:18

I try to give a more complete answer, since I struggled a bit implementing what was suggested above

Create a new folder

mkdir test_project cd test_project

First of all you will need to create a test.cpp with:

touch test.cpp

and then paste in the file the following:

#include <iostream>

int main(int argc, char** argv){
    std::cout << "Hello World" << std::endl;
    return 0;
}

in your CMakeLists.txt you should have something like the following:

project("test_proj")
cmake_minimum_required (VERSION 2.4) # this depends on what you are testing
find_package(Threads)
add_executable(test test.cpp)
target_link_libraries( test ${CMAKE_THREAD_LIBS_INIT} )

I hope this answer helps someone with the same problem.

What is the proper use of CMake FindThreads with modern C++?

2 Answers2