fix: Don't modify user-provided subdomains

Avoid modifying user-provided subdomain objects which breaks
Dask pickling/unpickling. Just register them with the grid
without changing their internal state.

Author: ggorman

examples/seismic/model.py

@@ -121,17 +121,16 @@ def __init__(self, origin, spacing, shape, space_order, nbl=20,
 
         # Create subdomains with grid parameter (new pattern)
         physdomain = PhysicalDomain(space_order, fs=fs, grid=self.grid)
-        new_subdomains = [physdomain]
-        for sd in subdomains:
-            # Update grid for any user-provided subdomains
-            sd.grid = self.grid
-            new_subdomains.append(sd)
+        # Register physdomain
+        self.grid._subdomains = self.grid._subdomains + (physdomain,)
+
+        # Register user-provided subdomains
+        self.grid._subdomains = self.grid._subdomains + subdomains
+
         if fs:
             fsdomain = FSDomain(space_order, grid=self.grid)
-            new_subdomains.append(fsdomain)
-
-        # Manually update grid's _subdomains to include new subdomains
-        self.grid._subdomains = self.grid._subdomains + tuple(new_subdomains)
+            # Register fsdomain
+            self.grid._subdomains = self.grid._subdomains + (fsdomain,)
 
         self._physical_parameters = set()
         self.damp = None