Rename get_graph() -> execution_graph

Instead of having a generic get_graph()
it is nicer to have this function be named
closer to what it returns (the graph of tasks
to be executed) as well as make it a property
since it is more of a property of the engine.

Change-Id: I4bb458b1069d7e6877f1cc51d42bfc0d8c751951

taskflow/engines/action_engine/engine.py

@@ -74,7 +74,8 @@ class ActionEngine(base.EngineBase):
     def suspend(self):
         self._change_state(states.SUSPENDING)
 
-    def get_graph(self):
+    @property
+    def execution_graph(self):
         self.compile()
         return self._root.graph
 
@@ -131,6 +132,7 @@ class ActionEngine(base.EngineBase):
                        result=result)
         self.task_notifier.notify(state, details)
 
+    @lock_utils.locked
     def compile(self):
         if self._root is not None:
             return

taskflow/tests/unit/test_action_engine.py

@@ -582,14 +582,14 @@ class EngineGraphFlowTest(EngineTestBase):
             TestTask(name='task2'))
 
         engine = self._make_engine(flow)
-        graph = engine.get_graph()
+        graph = engine.execution_graph
         self.assertTrue(isinstance(graph, networkx.DiGraph))
 
     def test_task_graph_property_for_one_task(self):
         flow = TestTask(name='task1')
 
         engine = self._make_engine(flow)
-        graph = engine.get_graph()
+        graph = engine.execution_graph
         self.assertTrue(isinstance(graph, networkx.DiGraph))