Move atom action handlers to there own subfolder/submodule

Since action handlers are atom specific it seems appropriate
to place the handlers under a specific submodule so that the
action engine module/folder layout is more obvious and makes
more sense.

This also adds on a handles(atom) method to those handlers
so that the runtime module/class can use those methods to
determine which handler should handle resetting an atom to
its initial state.

Change-Id: I7067d91347b41613fba1492d81d68a590f22c467

taskflow/engines/action_engine/actions/retry.py

@@ -17,7 +17,7 @@
 import logging
 
 from taskflow.engines.action_engine import executor as ex
-from taskflow import retry as rt
+from taskflow import retry as retry_atom
 from taskflow import states
 from taskflow.types import failure
 from taskflow.types import futures
@@ -28,19 +28,25 @@ SAVE_RESULT_STATES = (states.SUCCESS, states.FAILURE)
 
 
 class RetryAction(object):
+    """An action that handles executing, state changes, ... of retry atoms."""
+
     def __init__(self, storage, notifier, walker_factory):
         self._storage = storage
         self._notifier = notifier
         self._walker_factory = walker_factory
         self._executor = futures.SynchronousExecutor()
 
+    @staticmethod
+    def handles(atom):
+        return isinstance(atom, retry_atom.Retry)
+
     def _get_retry_args(self, retry, addons=None):
         scope_walker = self._walker_factory(retry)
         kwargs = self._storage.fetch_mapped_args(retry.rebind,
                                                  atom_name=retry.name,
                                                  scope_walker=scope_walker)
         history = self._storage.get_retry_history(retry.name)
-        kwargs[rt.EXECUTE_REVERT_HISTORY] = history
+        kwargs[retry_atom.EXECUTE_REVERT_HISTORY] = history
         if addons:
             kwargs.update(addons)
         return kwargs
@@ -103,7 +109,7 @@ class RetryAction(object):
 
         self.change_state(retry, states.REVERTING)
         arg_addons = {
-            rt.REVERT_FLOW_FAILURES: self._storage.get_failures(),
+            retry_atom.REVERT_FLOW_FAILURES: self._storage.get_failures(),
         }
         fut = self._executor.submit(_execute_retry,
                                     self._get_retry_args(retry,

taskflow/engines/action_engine/actions/task.py

@@ -17,6 +17,7 @@
 import logging
 
 from taskflow import states
+from taskflow import task as task_atom
 from taskflow.types import failure
 
 LOG = logging.getLogger(__name__)
@@ -25,6 +26,7 @@ SAVE_RESULT_STATES = (states.SUCCESS, states.FAILURE)
 
 
 class TaskAction(object):
+    """An action that handles scheduling, state changes, ... of task atoms."""
 
     def __init__(self, storage, task_executor, notifier, walker_factory):
         self._storage = storage
@@ -32,6 +34,10 @@ class TaskAction(object):
         self._notifier = notifier
         self._walker_factory = walker_factory
 
+    @staticmethod
+    def handles(atom):
+        return isinstance(atom, task_atom.BaseTask)
+
     def _is_identity_transition(self, state, task, progress):
         if state in SAVE_RESULT_STATES:
             # saving result is never identity transition

taskflow/engines/action_engine/runtime.py

@@ -14,16 +14,14 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+from taskflow.engines.action_engine.actions import retry as ra
+from taskflow.engines.action_engine.actions import task as ta
 from taskflow.engines.action_engine import analyzer as an
 from taskflow.engines.action_engine import completer as co
-from taskflow.engines.action_engine import retry_action as ra
 from taskflow.engines.action_engine import runner as ru
 from taskflow.engines.action_engine import scheduler as sched
 from taskflow.engines.action_engine import scopes as sc
-from taskflow.engines.action_engine import task_action as ta
-from taskflow import retry as retry_atom
 from taskflow import states as st
-from taskflow import task as task_atom
 from taskflow.utils import misc
 
 
@@ -93,9 +91,10 @@ class Runtime(object):
     def reset_nodes(self, nodes, state=st.PENDING, intention=st.EXECUTE):
         for node in nodes:
             if state:
-                if isinstance(node, task_atom.BaseTask):
-                    self.task_action.change_state(node, state, progress=0.0)
-                elif isinstance(node, retry_atom.Retry):
+                if self.task_action.handles(node):
+                    self.task_action.change_state(node, state,
+                                                  progress=0.0)
+                elif self.retry_action.handles(node):
                     self.retry_action.change_state(node, state)
                 else:
                     raise TypeError("Unknown how to reset atom '%s' (%s)"