Calls to getUniqueId/getUniqueIds can be given a foreign Dali reference.
However, the common case is where no foreignnode is supplied and the 'local' environment uid allocator is used.

However, in both cases, it lock a mutex and loops through a list of allocators (to find one that matches the supplied foreignnode).

It should have an allocator for the common case and avoid looking in the array of allocators for foreignnodes.