Thanks a lot for the corrections.
However, it's still executing just one thread, I don't see two hello
messages.
I'm using Octave 3.2.4 and gcc 4.1.1
Regards
Jaroslav Hajek wrote:
> 2010/4/15 "Miguel A. Vázquez" <mavazq...@cttc.es>:
>
>> Hello all,
>>
>> I am trying to implement some code in OpenMP under Octave, but I have
>> some problems.
>>
>> #include <omp.h>
>> #include <octave/oct.h>
>>
>> DEFUN_DLD (pmean, args, , "Calculates then mean in parallel")
>> {
>> int nargin = args.length ();
>>
>> Matrix m (1,1);
>>
>>
>> int tid,nthreads;
>> omp_set_num_threads(2);
>> #pragma omp parallel private( nthreads, tid)
>> tid = omp_get_thread_num();
>> nthreads = omp_get_num_threads();
>> octave_stdout << "Thread "<< tid << " of " << nthreads << "
>> threads \n.";
>> if (nargin != 1)
>> print_usage ();
>> else
>> {
>> NDArray A = args(0).array_value ();
>>
>>
>>
>> #pragma omp parallel for reduction(+:m)
>> for (octave_idx_type i = 0; i < A.nelem (); i++){
>> m = m + A.elem (i)/A.nelem ();
>> }
>>
>> return octave_value (m);
>>
>> }
>>
>> }
>>
>> This code is supposed to calculate a mean of an Octave matrix in
>> parallel: some iterations of the for will be done by different threads.
>>
>> I set the number of threads to 2 (omp_set_num_threads(2)). I compiled
>> and linked it nicely but, unfortunatelly, when I executed it:
>>
>> octave:1> pmean([10 0 5])
>> Thread 0 of 1 threads
>> .ans = 5
>>
>> One thread is executed instead. I don't really know how to solve this
>> problem, even don't know where I have to look for. Does anyone of you
>> have treated this problem before?
>>
>> Thank you in advance,
>>
>> Miguel
>>
>>
>
> I think you lack some basic OpenMP knowledge. In C++, omp parallel
> applies only to the next statement or block, so the way you've written
> it it doesn't make much sense. Use omp critical for I/O to make it
> atomic.
> You didn't initialize m; besides, you must use a primitive type for
> reduction clause. Also be aware that each DEFUN must return a value or
> throw an exception, just like every C++ function.
>
> This version works for me:
>
> DEFUN_DLD (pmean, args, , "Calculates then mean in parallel")
> {
> int nargin = args.length ();
> octave_value retval;
>
> omp_set_num_threads(2);
>
> #pragma omp parallel
> {
> int tid,nthreads;
> tid = omp_get_thread_num();
> nthreads = omp_get_num_threads();
> // WARNING: I/O not thread safe
> #pragma omp critical
> octave_stdout << "Thread "<< tid << " of " << nthreads << " threads.
> \n";
> }
>
> if (nargin != 1)
> print_usage ();
> else
> {
> const NDArray A = args(0).array_value ();
>
> double m = 0;
> #pragma omp parallel for reduction(+:m)
> for (octave_idx_type i = 0; i < A.nelem (); i++)
> m += A.elem (i) / A.nelem ();
>
> retval = m;
> }
>
> return retval;
> }
>
> hth
>
>
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