Mex OpenMP C code

Hi,

I tried to use OpenMP in Matlab 2018a. My code is very simple, called testOpenMP.c.

I successfully compiled the code by mex -v testOpenMP.c CFLAGS="$CFLAGS -fopenmp" LDFLAGS="$LDFLAGS -fopenmp"

However, we I run the compile mex extension by just typing testOpenMP in Matlab's command window. It always crashed.

Do you know how to correctly compile such an openmp c code and run it?

Thanks,

#include "mex.h"
#include "math.h"
#include "stdio.h"
#include <omp.h>

void mexFunction(
        int nargout,
        mxArray *pargout [ ],
        int nargin,
        const mxArray *pargin  [ ]
        ) {
    
    int thread_count = 32;
#pragma omp parallel for default(none)
for(int i = 0; i < 32; i++)
{
    printf("Hello from %d\n",i);
}

}

[Jan]

I've formatted the code to make it readable. You can do this by your own also.

What do you observe? "It always crashed" is not really clear.

[Yangyang Xu]

Whenever I ran the compiled code, the Matlab automatically shuts down.

[Jan]

Does this happen also, if you omit the #pragma line?

Which compiler do you use?

[Yangyang Xu]

It will not happen if I omit the #pragma line.

I used gcc 6.5

[Sushant Mahajan]

Did you find any solution? I am facing the exact same issue with a FORTRAN subroutine using MEX configured with a gfortran-6 compiler.

It runs fine when it is compiled without the -fopenmp flag, but MATLAB shuts down when the subroutine is called after using the -fopenmp flag during compilation. This happens even if I do not use any OMP_PARALLEL (equivalent to C's #pragma omp parallel) construct in the code.

Answer 1

[Arwel]

This thread maybe has what you need.... https://www.mathworks.com/matlabcentral/answers/381180-how-to-compile-matlab-library-with-c-including-openmp

Answer 2

[sjhstone]

Both printf and mexPrintf are not thread-safe and should be avoided in multi-thread OpenMP MEX C codes.

You can get more information at https://walkingrandomly.com/?p=1795