Hi perl monks, I am new to Perl but I could write a program that computes a mandelbrot set. I wanted to make it more efficient by using one of the three technologies XS, SWIG or Inline::C.

So I compiled in each case using or indicating the '-fopenmp' flags and '-lgomp' library but for the XS and inline::C methods it doesn't work, I mean even if I set the OMP_NUM_THREADS variable to a value greater than one, I always have one thread running

For SWIG I could see two or 4 threads running.

Here is for example the code for XS in the file mandelbrot.c and mandelbrot.h that I put in the Mandelbrot directory

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

int escapes(double cr, double ci, int it) {
  double zr = 0;
  double zi = 0;
  double zrtmp;
  int i;
  
  for(i=0; i<it; i++) {
    // z <- z^2 + c
    zrtmp = zr*zr - zi*zi + cr;
    zi = 2*zr*zi + ci;
    zr = zrtmp;
    if (zr*zr + zi*zi > 4) {
      return 1;
    }
  }
  return 0;
}

void mandel(double xmin, double xmax, int xstep, double ymin, double y
+max, int ystep, int iters) {
  int yc;
  
  // array of string to store result
  char *m = (char *) malloc(ystep * (xstep + 1) * sizeof(char));

  #pragma omp parallel for  
  for(yc=0; yc<ystep; yc++) {
    double y = yc*(ymax-ymin)/ystep + ymin;
    int xc;
    for(xc=0; xc<xstep; xc++) {
      double x = xc*(xmax-xmin)/xstep + xmin;
      escapes(x, y, iters);
      if (escapes(x, y, iters)) {
        m[yc * (xstep + 1) + xc] = ' ';
      } else {
        m[yc * (xstep + 1) + xc] = 'X';   
      }
    }
    // add end of string
    m[yc * (xstep+1) + xstep] = '\0';  
    
  }
  
  for(yc=0; yc<ystep; yc++) {
      printf("%s\n", &m[yc * (xstep+1)]);
  }
  
  free(m);
}

[download]
// mandelbrot.h
void mandel(double xmin, double xmax, int xstep, double ymin, double y
+max, int ystep, int iters);

[download]

And here the mandelbrot_xs.pl that uses the Mandelbrot module :

use warnings;
use Mandelbrot;
 
Mandelbrot::mandel(-2.0, 1.0, 256, -1.0, 1.0, 256, 100000);

[download]

I followed the following steps:

  1. h2xs -n Mandelbrot -O -x -F '-I..' Mandelbrot/mandelbrot.h
  2. cd Mandelbrot
  3. I modified Makefile.PL with 
        LIBS      => ['-lgomp'], # e.g., '-lm'
    CCFLAGS   => '-fopenmp',

    [download]
  4. perl Makefile.PL
  5. make
  6. make install
  7. cd ..
  8. perl mandelbrot_xs.pl

At the end it compiles and runs but always with ONE thread although I am using :

export OMP_NUM_THREADS=2

In reply to Why openMP is not taken into account by XS and inline::C by jmricher70

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