How to import OpenMP and MPI to a large CLion CMake project?

Question

I am new to OpenMP and MPI, and I want to import OpenMP and MPI to my existing CMake project. Therefore --

First, I created a very simple MPI project.

main.cpp:

#include "mpi.h"
#include "iostream"

int main(int argc, char** argv){
    MPI_Init(NULL, NULL);

    int world_size;
    MPI_Comm_size(MPI_COMM_WORLD, &world_size);

    int world_rank;
    MPI_Comm_rank(MPI_COMM_WORLD, &world_rank);

    char processor_name[MPI_MAX_PROCESSOR_NAME];
    int name_len;
    MPI_Get_processor_name(processor_name, &name_len);

    printf("Hello world from processor %s, rank %d out of %d processors\n",processor_name, world_rank, world_size);

    MPI_Finalize();
}

I can successfully compile and run the project using the command:

$ mpicxx main.cpp -o main.out
$ mpirun -np 2 main.out

Then I created and configurated a CMake project using CLion. I can also successfully compile and run it using CLion, but it only used one processor.

CMakeLists.txt:

cmake_minimum_required(VERSION 3.5)
project(Test)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")

find_package(MPI)
include_directories(${MPI_INCLUDE_PATH})

SET(CMAKE_CXX_COMPILER mpicxx)
SET(CMAKE_C_COMPILER  mpicc)

set(SOURCE_FILES main.cpp)
add_executable(Test ${SOURCE_FILES})

Thus my first question is how can I use multiple processors using CLion?

Second, I created a simple OpenMP project and run successfully.

But my second question is how can I include both MPI and OpenMP? It seems that I cannot just merge the two CMakeLists.txt of the MPI project and OpenMP project. Because I got an error about the -fopenmp flag:

clang: error: unsupported option '-fopenmp'

CMakeLists.txt:

cmake_minimum_required(VERSION 3.12)
project(OpenMP_MPI)

set(CMAKE_CXX_STANDARD 14)

OPTION (USE_OpenMP "Use OpenMP to enamble <omp.h>" ON)

if(APPLE)
    set(CMAKE_C_COMPILER "/usr/local/Cellar/llvm/9.0.0_1/bin/clang")
    set(CMAKE_CXX_COMPILER "/usr/local/Cellar/llvm/9.0.0_1/bin/clang++")
    set(OPENMP_LIBRARIES "/usr/local/Cellar/llvm/9.0.0_1/lib")
    set(OPENMP_INCLUDES "/usr/local/Cellar/llvm/9.0.0_1/include")
    if(CMAKE_C_COMPILER_ID MATCHES "Clang")
        set(OpenMP_C "${CMAKE_C_COMPILER}")
        set(OpenMP_C_FLAGS "-fopenmp=libomp -Wno-unused-command-line-argument")
        set(OpenMP_C_LIB_NAMES "libomp" "libgomp" "libiomp5")
        set(OpenMP_libomp_LIBRARY ${OpenMP_C_LIB_NAMES})
        set(OpenMP_libgomp_LIBRARY ${OpenMP_C_LIB_NAMES})
        set(OpenMP_libiomp5_LIBRARY ${OpenMP_C_LIB_NAMES})
    endif()
    if(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
        set(OpenMP_CXX "${CMAKE_CXX_COMPILER}")
        set(OpenMP_CXX_FLAGS "-fopenmp=libomp -Wno-unused-command-line-argument")
        set(OpenMP_CXX_LIB_NAMES "libomp" "libgomp" "libiomp5")
        set(OpenMP_libomp_LIBRARY ${OpenMP_CXX_LIB_NAMES})
        set(OpenMP_libgomp_LIBRARY ${OpenMP_CXX_LIB_NAMES})
        set(OpenMP_libiomp5_LIBRARY ${OpenMP_CXX_LIB_NAMES})
    endif()
endif()

find_package(OpenMP REQUIRED)
if (OPENMP_FOUND)
    if(APPLE)
        include_directories("${OPENMP_INCLUDES}")
        link_directories("${OPENMP_LIBRARIES}")
    endif()
    set (CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${OpenMP_C_FLAGS}")
    set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${OpenMP_CXX_FLAGS}")
    # set (CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} ${OpenMP_EXE_LINKER_FLAGS}")
endif(OPENMP_FOUND)

find_package(MPI REQUIRED)
include_directories(${MPI_INCLUDE_PATH})

SET(CMAKE_CXX_COMPILER mpicxx)
SET(CMAKE_C_COMPILER  mpicc)

add_executable(OpenMP_MPI main.cpp)

Answer 1

The CMakeLists.txt should not be so complicated. It should be like this:

cmake_minimum_required(VERSION 3.12)
project(OpenMP_MPI)

set(CMAKE_CXX_STANDARD 14)

find_package(MPI REQUIRED)
include_directories(SYSTEM ${MPI_INCLUDE_PATH})

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fopenmp")

add_executable(OpenMP_MPI main.cpp)

target_link_libraries(OpenMP_MPI ${MPI_C_LIBRARIES})

For linux, you should use the following command to build and run.

mkdir build && cd build && cmake .. && make && mpirun -n 2 ./OpenMP_MPI

For MacOS, just change the command to

mkdir build && cd build && cmake -DCMAKE_CXX_COMPILER=g++-9 .. && make && mpirun -n 2 ./OpenMP_MPI

It should work. (You can go to /usr/local/bin to check whether your compiler is g++-9.)