Cache mesh bounding boxes correctly

[leo-collins]

After changing mesh coordinates, accessing mesh.bounding_box_coords will now recalculate the bounding boxes.

Added a mesh._check_coordinate_dat_version helper because this sort of thing happens in a few places (bounding boxes, rtree, soon to be distributed rtree)

[connorjward]

The really nice way to do this is:

def cached_property_until(cond: Callable[[Self], bool]):
  def decorator(func):
    def wrapper(self):
      if cond(self):
        return self._cache[some key]
      else:
        return self._cache.setdefault(some key, func(self))

cached_property_until_coords_change = cached_property_until(lambda self: self._saved_coords_dat_version == self.coordinates.dat.dat_version)

so you can have

@cached_property_until_coords_change
def bounding_box_coords(self):
  ...

[connorjward]

@achanbour this is very relevant to your work, and you have already probably done something similar. Any comments?

[achanbour]

I currently have an attribute that keeps track of the mesh's topology mesh._topology_version (under VertexOnlyMesh only for now). It gets incremented by MeshUpdater (not yet in Firedrake) when the VOM points get redistributed or increase/decrease in number. This does not get incremented when the coordinates change (provided the topology stays the same).

In both regimes (coordinates change OR topology changes), the MeshUpdater clears the cached mesh.bounding_box_coords. I suppose with Leo's change, I can simply remove the line in the updater that clears this cache.

[connorjward]

What's this for?

[leo-collins]

cached_property_until stores the rtree in self._rtree_cache. That method clear_rtree is public API (I know thetis are using it). Maybe it can be deprecated now, I'm not sure.

[connorjward]

Without context this line makes no sense. I would prefer to hide it as much as possible. Why not:

def clear_rtree(self):
  # comment about why this does the right thing
  self._rtree_cache = None

We should definitely look to deprecate clear_rtree because we can manage it ourselves.