How do I parallelize a for loop through a C++ std::list using OpenMP?

Question

I would like to iterate through all elements in an std::list in parallel fashion using OpenMP. The loop should be able to alter the elements of the list. Is there a simple s

Answer 1

Without using OpenMP 3.0 you have the option of having all threads iterating over the list:

std::list::iterator it;
#pragma omp parallel private(it)
{
   for(it = list1.begin(); it!= list1.end(); it++)
   {
      #pragma omp single nowait
      {
         it->compute();
      }
   } 
} 

In this case each thread has its own copy of the iterator (private) but only a single thread will access a specific element (single) whereas the other threads will move forward to the next items (nowait)

Or you can loop once to build a vector of pointers to be then distributed among threads:

std::vector< T*> items;

items.reserve(list.size());
//put the pointers in the vector
std::transform(list.begin(), list.end(), std::back_inserter(items), 
               [](T& n){ return &n; }
);

#pragma omp parallel for
for (int i = 0; i < items.size(); i++)
{
  items[i]->compute();
}

Depending on your specific case one or the other can be faster. Testing which one suits you better is easy.