Add utility member functions for partitioned_vector

[atrantan]

This pull request does 2 small changes:

• Give a public access to the type named data_type in hpx::server::partitioned_vector
• Add a member action (get_copied_data) allowing to asynchronously get a copy of the data
  owned by the server

[hkaiser]

This should probably be: for(auto const& part_data : partitions_)

[atrantan]

Done in commit 239ed21

[hkaiser]

Thanks. Just out of curiosity: why do you need this functionality?

[atrantan]

It allows my array_view to get all it needs to return the data of a partition. Saving the ids is costless as well.

[hkaiser]

Hmmm, the idea was for the array_view to access the local data only. Why do you need to get a copy of the local data for this? Wouldn't it be no view anymore?

[hkaiser]

Sorry, misunderstanding - what I wanted to ask is why you need the get_copied_data() functionality above.

[atrantan]

This is for another functionality extending the concept of array_view. If an owner of a array_view needs a data that is not in its locality, make a copy and return it by value.

[hkaiser]

This is for another functionality extending the concept of array_view. If an owner of a array_view needs a data that is not in its locality, make a copy and return it by value.

Well, let's talk about this in more detail. I'm not convinced yet.

Wrt get_partitions_ids(): I don't think you need to add this as all you need for the local access is to create the proper iterators. For instance:

typedef typename hpx::partitioned_vector<int>::iterator iterator;
typedef hpx::traits::segmented_iterator_traits<iterator> traits;

hpx::id_type here = hpx::find_here();
hpx::partitioned_vector<int> v(...);

// extract iterators representing local data segments
auto segment_end = v.segment_end(here);
for (auto seg_it = v.segment_begin(here); seg_it != segment_end; ++seg_it)
{
    // extract iterators allowing to (natively) access local data
    auto local_it = traits::begin(seg_it);
    auto local_end = traits::end(seg_it);

    // [local_it, local_end) represents the local data, the iterators
    // are essentially equivalent to the iterators exposed by the 
    // underlying data
}

So, you can use the exposed iterators directly without even accessing the partition table inside the partitioned_vector.