compiling openmp, macports gcc, and eclipse cdt

问题

I am newbie in openmp. The following is the environment.

OS : Mac OSX Mavericks
Compiler : gcc (MacPorts gcc48 4.8.2_0) 4.8.2
IDE : Eclipse Kepler CDT plugin

I wrote the following openmp program

#include < stdio.h>  
#include < omp.h>  

int main()  
{
#pragma omp parallel
{
    int i=omp_get_thread_num();
    printf("hello (%d)",i);
    printf("world (%d)",i);
  }
}

I compiled the above program and got the error that omp.h is not found and lgomp not found. Hence I added in the project properties an include path with /opt/local/lib/gcc48/gcc/x86_64-apple-darwin13/4.8.2/include and a library path /opt/local/lib/gcc48. The include path had the omp.h file and the library path had the file libomp.o.

I include the -fopenmp option in both the linker and the compiler option through project properties. It is compiling with gcc -I/opt/local/lib/gcc48/gcc/x86_64-apple-darwin13/4.8.2/include -O0 -g3 -Wall -c -fmessage-length=0 -fopenmp -MMD -MP -MF"src/OpenMPCourseExamples.d" -MT"src/OpenMPCourseExamples.d" -o "src/OpenMPCourseExamples.o" "../src/OpenMPCourseExamples.c" and linking with the command "gcc -L/opt/local/lib/gcc48 -fopenmp -o "OpenMPCourseExamples" ./src/OpenMPCourseExamples.o".

With the above command it compiles without an error but with a warning - "warning: unknown pragma ignored [-Wunknown-pragmas] #pragma omp parallel".

Also, I set an environment variable in the launch properties with OMP_NUM_THREADS=4. I ran the program that compiled with the above warning. I am getting only "hello (0)world (0)". I was under the impression that I should start four threads and should see the other outputs of "hello(1)world(1)hello(2)world(2)hello(3)world(3)" in some ordering as well. Now, here are my following questions.

Why am I getting the #pragma warning?
Is the compiler really detecting the openmp and building with openmp?
If everything is correct, why am I not seeing four different threads getting started?

回答1:

MacPorts configures the GCC build process with --program-suffix=-mp-${major} and therefore all compiler executables have the -mp-4.8 suffix. When you call gcc, you end up using Apple's Clang compiler, which does not support OpenMP and therefore does not recognise the -fopenmp option and #pragma omp ....

You have to do the following changes to the project settings:

Change the compiler command to gcc-mp-4.8
Change the linker command to gcc-mp-4.8
Remove the explicit specification of the include and library paths since the presence of -fopenmp adds them automatically.

回答2:

The final steps that worked for openmp, macports gcc compiler, eclipse CDT in mac osx mavericks are.

Enable "Make ToolChain(s) Preferred" in Eclipse->Preference->C/C++->New C/C++ Project Wizard.
sudo port select --list gcc and set it sudo port select --set gcc with mp-gcc.
File->New Project->C Project (not C++) and create a hello world project.
In Project->Properties->C/C++ Build->Settings->Tool Settings set the following. (a) GCC C Compiler to /opt/local/bin/gcc-mp-4.8 (b)MAC OSX Linker to /opt/local/bin/gcc-mp-4.8
Build the hello world project and make sure, it compiles and runs successfully.
Include the open mp code. The code asked in the question of this page.
Go to again Project->Properties->C/C++ Build->Settings->Tool Settings set the following. (a) GCC Compiler ->Miscellaneous add -fopenmp (b) MacOSx Linker->Miscellaneous set -fopenmp
Build the code again.

The above steps worked good for me.

来源：https://stackoverflow.com/questions/20489813/compiling-openmp-macports-gcc-and-eclipse-cdt

标签

openmp