Re: OpenMP problem

[Jerry DeLisle <jvdelisle at verizon dot net>]

Carlos Alberto Bulant wrote:
> Hello,
>
> I'm using cygwin, gfortran-4 compiler, in NetBeans IDE. My pc has WinXP SP3.
>
> I'm trying to introduce parallel processing to my project, i've been
> reading about OpenMP, so i make this litle code to test it:
>
> //-------------------------------------------------------------------------------------------------
>     PROGRAM HELLO
> !$      USE omp_lib
>
>        INTEGER n, i
>        PARAMETER (n=505150)
>        REAL X(n)
>
>
> !$      call omp_set_num_threads(2)
>        write(6, "(a, i3)") " OpenMP max threads: ",
>     +        OMP_GET_MAX_THREADS()
>
> !$OMP PARALLEL
>        write(6, "(2(a,i3))") " OpenMP: N_threads = ",
>     +      OMP_GET_NUM_THREADS(), " thread = ", OMP_GET_THREAD_NUM()
> !$OMP END PARALLEL
>
>
> !$OMP   PARALLEL DO
> !$OMP+  SHARED(X)
> !$OMP+  PRIVATE(i)
>              DO i = 1, n
>                 X(i) = i
> !$              !write(*, *) "  From Thread = ", OMP_GET_THREAD_NUM(), " i= ",i
>              END DO
> !$OMP   END PARALLEL DO
>
>      END PROGRAM
> //-------------------------------------------------------------------------------------------------
>
> The program runs ok with n<= 505150
> with 505150 > n >= 505170 The output is from one thread only
> with n > 505170 i get a runtime error, the cause is stack overflow.
>
> i set windows environment variables
> OMP_STACKSIZE=10000
> GOMP_STACKSIZE=10000
>
> but i get the same behaviour...
>
> any ideas???

It could be you are just too big for your machine.  Also, when you set 
environment variables, they do not always 'take' to cygwin terminals that are 
already open, so you may want to close and reopen everything after setting 
environment variables.

Although I do build a gfortran binary for Cygwin and I use Cygwin on occasion 
for real work, I am not a big fan of using windows for serious work.  At the 
Cygwin web site there are discussions about non-Cygwin apps that do things that 
interfere called BLODA I think. Flip side, Cygwin actually works pretty damn 
good most of the time.

Also, check your question at comp.lang.fortran news list.  Those folks have a 
lot of combined experience.

Jerry