Avoid default serialization of classes in dump_attrs

For playbook base objects, when dumping attributes via dump_attrs() an
attribute like loop_control is a class. Using the default serialization
for these is slow and consumes a lot of memory. Since LoopControl is also
based on the Base class, we can use serialize() instead and save a lot of
resources.

This also adds a from_attrs() complimentary method to nicely turn the
dumped attrs back into proper field attributes.

Fixes ansible#23579

lib/ansible/playbook/base.py

@@ -506,10 +506,28 @@ def dump_attrs(self):
         Dumps all attributes to a dictionary
         '''
         attrs = dict()
-        for name in self._valid_attrs.keys():
-            attrs[name] = getattr(self, name)
+        for (name, attribute) in iteritems(self._valid_attrs):
+            attr = getattr(self, name)
+            if attribute.isa == 'class' and attr is not None and hasattr(attr, 'serialize'):
+                attrs[name] = attr.serialize()
+            else:
+                attrs[name] = attr
         return attrs
 
+    def from_attrs(self, attrs):
+        '''
+        Loads attributes from a dictionary
+        '''
+        for (attr, value) in iteritems(attrs):
+            if attr in self._valid_attrs:
+                attribute = self._valid_attrs[attr]
+                if attribute.isa == 'class' and isinstance(value, dict):
+                    obj = attribute.class_type()
+                    obj.deserialize(value)
+                    setattr(self, attr, obj)
+                else:
+                    setattr(self, attr, value)
+
     def serialize(self):
         '''
         Serializes the object derived from the base object into

lib/ansible/plugins/strategy/__init__.py

@@ -332,8 +332,7 @@ def parent_handler_match(target_handler, handler_name):
             found_task = iterator.get_original_task(original_host, task_result._task)
             original_task = found_task.copy(exclude_parent=True, exclude_tasks=True)
             original_task._parent = found_task._parent
-            for (attr, val) in iteritems(task_result._task_fields):
-                setattr(original_task, attr, val)
+            original_task.from_attrs(task_result._task_fields)
 
             task_result._host = original_host
             task_result._task = original_task