Merge "Add comments for deletion of ARQs by instance or ARQ UUIDs."

cyborg/api/controllers/v2/arqs.py

@@ -214,6 +214,14 @@ class ARQsController(base.CyborgController):
             DELETE /v2/accelerator_requests?arqs=uuid1,uuid2,...
             DELETE /v2/accelerator_requests?instance=uuid
 
+        The second form is idempotent, i.e., it would have the same effect
+        if called repeatedly with the same instance UUID. In other words,
+        it would not raise an error on the second and later attempts even if
+        the first one has deleted the ARQs. Whereas the first form is not
+        idempotent: if one or more of the ARQs do not exist, it would raise
+        an error. Nova uses the second form: so repeated calls do not cause
+        issues.
+
         :param arq: List of ARQ UUIDs
         :param instance: UUID of instance whose ARQs need to be deleted
         """

cyborg/objects/ext_arq.py

@@ -149,6 +149,12 @@ class ExtARQ(base.CyborgObject, object_base.VersionedObjectDictCompat,
 
     @classmethod
     def delete_by_uuid(cls, context, arq_uuid_list):
+        """Delete a list of ARQs based on their UUIDs.
+
+        This is not idempotent, i.e., if the first call to delete an
+        ARQ has succeeded, second and later calls to delete the same ARQ
+        will get errored out.
+        """
         for uuid in arq_uuid_list:
             obj_extarq = objects.ExtARQ.get(context, uuid)
             # TODO() Defer deletion to conductor
@@ -158,7 +164,13 @@ class ExtARQ(base.CyborgObject, object_base.VersionedObjectDictCompat,
 
     @classmethod
     def delete_by_instance(cls, context, instance_uuid):
-        """Delete all ARQs for given instance."""
+        """Delete all ARQs for given instance.
+
+        This is idempotent, i.e., it would have the same effect if called
+        repeatedly with the same instance UUID. In other words, it would
+        not raise an error on the second and later attempts even if the
+        first one has deleted the ARQs.
+        """
         obj_extarqs = [extarq for extarq in objects.ExtARQ.list(context)
                        if extarq.arq['instance_uuid'] == instance_uuid]
         for obj_extarq in obj_extarqs: