  We discuss parallel algorithms to gather topological information about
off-process mesh neighbor elements. This information is commonly called the
ghost layer, whose creation is a fundamental, necessary task in executing most
parallel, element-based computer simulations. Approaches differ in that the
ghost layer may either be inherently part of the mesh data structure that is
maintained and modified, or kept separate and constructed/deleted as needed.
  In this work, we present an updated design following the latter approach,
which we favor for its modularity of algorithms and data structures. We target
arbitrary adaptive, non-conforming forest-of-(oc)trees meshes of mixed element
shapes, such as cubes, prisms, and tetrahedra, and restrict ourselves to
face-ghosts. Our algorithm has low complexity and redundancy since we reduce it
to generic codimension-1 subalgorithms that can be flexibly combined. We cover
several existing solutions as special cases and optimize further using
recursive, amortized tree searches and traversals.
