I have a big vector. I would like to increment only positive member in parallel.
class is_positive_number {
public:
bool operator()(int x) { return 0 < x; }
};
int main()
{
int numbers_[] = { 0, -1, 4, -3, 5, 8, -2, 3, 4, -1 };
const int N = sizeof(numbers_) / sizeof(int);
std::vector<int> test_vec(numbers_, numbers_ + N);
std::cout << "max: " << omp_get_max_threads() << std::endl;
int number_of_threads = 4;
int SubVecLen = N / number_of_threads,
LeftOvers = N % number_of_threads;
int k = 0, i = 0, n = 0;
std::vector<int> start_vec, end_vec;
while (n < number_of_threads)
{
k += i;
i = (SubVecLen + (LeftOvers-- > 0 ? 1 : 0));
start_vec.push_back(k);
end_vec.push_back((k + i - 1));
++n;
}
for (size_t n = 0; n < number_of_threads; n++)
{
std::cout << start_vec[n] << "\t" << end_vec[n] << "\n";
}
is_positive_number predicate;
typedef boost::filter_iterator<is_positive_number, std::vector<int>::iterator>
FilterIter;
#pragma omp parallel
{
#pragma omp for
for (int s = 0; s < 4; s++)
{
FilterIter filter_iter_first(predicate, test_vec.begin(), (test_vec.begin() + start_vec[omp_get_thread_num()]) );
FilterIter filter_iter_last(predicate, test_vec.begin(), (test_vec.begin() + end_vec[omp_get_thread_num()] + 1) );
for (auto iter = filter_iter_first;
iter != filter_iter_last; iter++)
{
std::cout << "num: " << *iter << std::endl;
(*iter) = (*iter) + 1;
}
}
}
for (size_t n = 0; n < test_vec.size(); n++)
{
std::cout << test_vec[n] << "\n";
}
return 0;
}
The result is wrong!
However the real problem I am trying to solve is more complicated than this one. I tried to simplify my question so that it would be more understandable. I have to also mention that I am restricted to use openMP v.2.0. That is why I tried to split my vector and dedicate each part of the vector to a specific thread.
Any idea would be appreciated.
You use the wrong start and stop indices when creating your filter iterators. I've attached a working example. I used s to select the thread inside the parallel for statement. Not sure if your version works too, so I changed it to what I'm used to.
#pragma omp parallel
{
#pragma omp for
for (int s = 0; s < 4; s++)
{
/* The following lines are important */
FilterIter filter_iter_first(predicate, test_vec.begin() + start_vec[s], (test_vec.begin() + end_vec[s] + 1));
FilterIter filter_iter_last(predicate, test_vec.begin() + end_vec[s] + 1, (test_vec.begin() + end_vec[s] + 1));
for (auto iter = filter_iter_first; iter != filter_iter_last; iter++)
{
std::cout << "num: " << *iter << std::endl;
(*iter) = (*iter) + 1;
}
}
}