LocalIndex in MFIter

[ankithadas]

Dear AMReX team,

Does LocalIndex() change if OMP tiling is used ? For example, would the following code be safe for tiling and non-tiling case.

    const auto* eb_factory = dynamic_cast<const amrex::EBFArrayBoxFactory*>(factory);
    auto const& flags = eb_factory->getMultiEBCellFlagFab();
    const auto& vfrac = eb_factory->getVolFrac();
    amrex::Vector<amrex::Long> num_covered_cells(vfrac.local_size());

#ifdef AMREX_USE_OMP
#pragma omp parallel if (amrex::Gpu::notInLaunchRegion())
#endif
    for (amrex::MFIter mfi(vfrac, false); mfi.isValid(); ++mfi)
    {
        const auto& bx = mfi.tilebox();
        const auto& flagfab = flags[mfi];
        const auto typ = flagfab.getType(bx);
        const int iLocal = mfi.LocalIndex();
        if (typ == amrex::FabType::regular) {
            num_covered_cells[iLocal] = 0;
        } else if (typ == amrex::FabType::covered) {
            num_covered_cells[iLocal] = bx.numPts();
        } else if (typ == amrex::FabType::singlevalued) {
            num_covered_cells[iLocal] = flagfab.getNumCoveredCells(bx);
        }
    }

[WeiqunZhang]

LocalIndex does not change if tiling is on. The code above is not safe for tiling and omp.

[ankithadas]

I am assuming that I would need to use atomic adds here.