Run a function of a dll in multiple threads

[HeLo]

As the faddeeva function is not available in LabVIEW, I have compiled the code of Steven G. Johnson  into a DLL using the GCC compiler in Code::Blocks - and it works (the same code is used also in SciPy, Matlab and others).

In order to improve in speed, I would like to run the function in a for-loop "enabling loop parallelism" or have it called by multiple clones of a reentrant "Faddeeva.vi".

However calling the function that way produces erroneous results - it looks like there is some interference between the different calls.

As native LabVIEW functions like "Integral x(t).vi" can do exactly this and as these functions also call a dll, I must have some statements in my dll that are not thread save.

Can anybody point me to the mistake, that prevents a correct multi threaded call?

Herbert

 

P.S.: Please find below a part of the c-file attached

#include <math.h>
#include <windows.h>
/* The Faddeeva.cc file contains macros to let it compile as C code
   (assuming C99 complex-number support), so just #include it. */
#include "Faddeeva.cc"
BOOL WINAPI DllMain (HINSTANCE hInst     /* Library instance handle. */ ,
                       DWORD reason        /* Reason this function is being called. */ ,
                       LPVOID reserved     /* Not used. */ )
{
    switch (reason)
    {
      case DLL_PROCESS_ATTACH:
        break;

      case DLL_PROCESS_DETACH:
        break;

      case DLL_THREAD_ATTACH:
        break;

      case DLL_THREAD_DETACH:
        break;
    }

    /* Returns TRUE on success, FALSE on failure */
    return TRUE;
}

/* LabVIEW created typedefs */
#pragma pack (1)
typedef struct {
    long dimSize;
    double elt[1];
    } TD1;
typedef TD1 **dArr;
double *Re_zArr, *Im_zArr, *RelErr_Arr, *Re_wArr, *Im_wArr;
double complex z, w;
int Npts;
int i;

_declspec(dllexport) void FaddeevaW(dArr x, dArr y, dArr RelErr, dArr Re_w, dArr Im_w);
_declspec(dllexport) void FaddeevaW(dArr x, dArr y, dArr RelErr, dArr Re_w, dArr Im_w)
{
  Npts = (*x)->dimSize;
  Re_zArr = & (*x)->elt[0];
  Im_zArr = & (*y)->elt[0];
  RelErr_Arr = & (*RelErr)->elt[0];
  Re_wArr = & (*Re_w)->elt[0];
  Im_wArr = & (*Im_w)->elt[0];
    for (i=0; i<Npts; i++)
        {
            w = Faddeeva_w((*Re_zArr + *Im_zArr*I), *RelErr_Arr);
            *Re_wArr = creal(w);
            *Im_wArr = cimag(w);
            Re_zArr++;
            Im_zArr++;
            RelErr_Arr++;
            Re_wArr++;
            Im_wArr++;
        }
}

 

 

 

Faddeeva.c Faddeeva.cc Faddeeva.h

[mhenz]

You created a couple of global variables. This is not thread save.

double *Re_zArr, *Im_zArr, *RelErr_Arr, *Re_wArr, *Im_wArr;
double complex z, w;
int Npts;
int i;

 

[HeLo]

Hi mhenz,

thank you very much!!!!

I corrected this and - it works 😃.

For all, who maybe have a need for it, I attach the corrected code (only the file "Faddeeva.c" was changed).

 

Herbert

Faddeeva.zip