Move seek providers with resource to context

This patch moves the resource look up to `RequestGroupSearchContext`
initialization. This enables us to reuse the results for
_get_providers_with_shared_capacity(). That optimization is coming
in a following patch.

Change-Id: I2796c3e93317edd3ae8b02fb038cc39f23b41840
Story: 2005712
Task: 31038

placement/objects/research_context.py

@@ -106,6 +106,19 @@ class RequestGroupSearchContext(object):
             LOG.debug("getting allocation candidates in the same tree "
                       "with the root provider %s", tree_ids.root_uuid)
 
+        self._rps_with_resource = {}
+        for rc_id, amount in self.resources.items():
+            # NOTE(tetsuro): We could pass rps in requested aggregates to
+            # get_providers_with_resource here once we explicitly put
+            # aggregates to nested (non-root) providers (the aggregate
+            # flows down feature) rather than applying later the implicit rule
+            # that aggregate on root spans the whole tree
+            provs_with_resource = get_providers_with_resource(
+                context, rc_id, amount, tree_root_id=self.tree_root_id)
+            if not provs_with_resource:
+                raise exception.ResourceProviderNotFound()
+            self._rps_with_resource[rc_id] = provs_with_resource
+
         # a dict, keyed by resource class ID, of the set of resource
         # provider IDs that share some inventory for each resource class
         # This is only used for unnumbered request group path where
@@ -143,6 +156,9 @@ class RequestGroupSearchContext(object):
     def get_rps_with_shared_capacity(self, rc_id):
         return self._sharing_providers.get(rc_id)
 
+    def get_rps_with_resource(self, rc_id):
+        return self._rps_with_resource.get(rc_id)
+
 
 def provider_ids_from_rp_ids(context, rp_ids):
     """Given an iterable of internal resource provider IDs, returns a dict,
@@ -346,8 +362,7 @@ def get_provider_ids_matching(rg_ctx):
     first = True
     for rc_id, amount in rg_ctx.resources.items():
         rc_name = rc_cache.RC_CACHE.string_from_id(rc_id)
-        provs_with_resource = get_providers_with_resource(
-            rg_ctx.context, rc_id, amount, tree_root_id=rg_ctx.tree_root_id)
+        provs_with_resource = rg_ctx.get_rps_with_resource(rc_id)
         LOG.debug("found %d providers with available %d %s",
                   len(provs_with_resource), amount, rc_name)
         if not provs_with_resource:
@@ -435,8 +450,7 @@ def get_trees_matching_all(rg_ctx):
         rc_name = rc_cache.RC_CACHE.string_from_id(rc_id)
 
         provs_with_inv_rc = rp_candidates.RPCandidateList()
-        rc_provs_with_inv = get_providers_with_resource(
-            rg_ctx.context, rc_id, amount, tree_root_id=rg_ctx.tree_root_id)
+        rc_provs_with_inv = rg_ctx.get_rps_with_resource(rc_id)
         provs_with_inv_rc.add_rps(rc_provs_with_inv, rc_id)
         LOG.debug("found %d providers under %d trees with available %d %s",
                   len(provs_with_inv_rc), len(provs_with_inv_rc.trees),

placement/tests/functional/db/test_allocation_candidates.py

@@ -222,13 +222,10 @@ class ProviderDBHelperTestCase(tb.PlacementDbBaseTestCase):
 
         # We don't get anything if the specified tree doesn't satisfy the
         # requirements in the first place
-        rg_ctx = _req_group_search_context(
-            self.ctx,
-            resources=resources,
-            in_tree=uuids.allused,
-        )
-        res = res_ctx.get_provider_ids_matching(rg_ctx)
-        self.assertEqual([], res)
+        self.assertRaises(exception.ResourceProviderNotFound,
+                          _req_group_search_context,
+                          self.ctx, resources=resources,
+                          in_tree=uuids.allused)
 
     def test_get_provider_ids_matching_with_multiple_forbidden(self):
         rp1 = self._create_provider('rp1', uuids.agg1)
@@ -417,6 +414,14 @@ class ProviderTreeDBHelperTestCase(tb.PlacementDbBaseTestCase):
             """Helper function to validate the test result"""
             # NOTE(jaypipes): get_trees_matching_all() expects a dict of
             # resource class internal identifiers, not string names
+            if not expected_trees:
+                try:
+                    self.assertRaises(exception.ResourceProviderNotFound,
+                                      _req_group_search_context,
+                                      self.ctx, **kwargs)
+                    return
+                except Exception:
+                    pass
             rg_ctx = _req_group_search_context(self.ctx, **kwargs)
             results = res_ctx.get_trees_matching_all(rg_ctx)