openmp for construction

[mpetri]

there would be quite a few places where we could speed things up using simple openmp primitives (similar to what libdivsufsort). for example:

        void construct_init_rank_select() {
            util::init_support(m_tree_rank, &m_tree);
            util::init_support(m_tree_select0, &m_tree);
            util::init_support(m_tree_select1, &m_tree);
        }

of course this would have to be disabled when you do "construction time experiments"

[simongog]

Yes, lets do this. In the example above we also don't have to worry about the working space, since its the same as in the serial version.

[mpetri]

I experimented with this and it seems to improve the construction time by a few percent. However, it required the memory manager (mm::add mm::remove) to be thread safe which it currently is not.

is there a way to only add mutexes to the mm::add mm::remove methods if we run in "multithreaded mode?" there is an openmp specific define but is there a define that we can check if sdsl code runs in multiple threads?

or should we make mm::add and mm::remove only do things if we enable it manually. like mm::enable = true; at the beginning of the program similar to the verbose flag.