From ee1d583721934cf6cec5c4d443ef66a39f9f6141 Mon Sep 17 00:00:00 2001
From: Joshua Harlow <harlowja@gmail.com>
Date: Sat, 12 Oct 2013 18:33:04 +0000
Subject: [PATCH] Add task state verification

Change-Id: I85abee2a1112ce1b9bb708cb9129f06c794f83b1
---
 taskflow/engines/action_engine/task_action.py | 13 ++++-
 taskflow/states.py                            | 51 ++++++++++++++++++-
 tools/state_graph.py                          | 10 +++-
 3 files changed, 70 insertions(+), 4 deletions(-)

diff --git a/taskflow/engines/action_engine/task_action.py b/taskflow/engines/action_engine/task_action.py
index bee0266f..0bf61878 100644
--- a/taskflow/engines/action_engine/task_action.py
+++ b/taskflow/engines/action_engine/task_action.py
@@ -55,8 +55,16 @@ class TaskAction(base.Action):
     def uuid(self):
         return self._id
 
-    def _change_state(self, engine, state, result=None, progress=None):
+    def _change_state(self, engine, state,
+                      result=None, progress=None, force=False):
         """Update result and change state."""
+        old_state = engine.storage.get_task_state(self.uuid)
+        state_check = states.check_task_transition(old_state, state)
+        if not force and not state_check:
+            # NOTE(harlowja): if we are forcing this state change, we don't
+            # care if the state transition should be ignored, if it's not being
+            # forced then we just ignore this state change.
+            return
         if state in RESET_TASK_STATES:
             engine.storage.reset(self.uuid)
         if state in SAVE_RESULT_STATES:
@@ -79,7 +87,8 @@ class TaskAction(base.Action):
                           task, self.uuid, progress)
 
     def _force_state(self, engine, state, progress, result=None):
-        self._change_state(engine, state, result=result, progress=progress)
+        self._change_state(engine, state,
+                           result=result, progress=progress, force=True)
         self._task.update_progress(progress)
 
     def execute(self, engine):
diff --git a/taskflow/states.py b/taskflow/states.py
index 07dc6e63..1ffed0b1 100644
--- a/taskflow/states.py
+++ b/taskflow/states.py
@@ -39,9 +39,10 @@ RESUMING = 'RESUMING'
 
 # Task states.
 FAILURE = FAILURE
-SUCCESS = SUCCESS
+PENDING = PENDING
 REVERTED = REVERTED
 REVERTING = REVERTING
+SUCCESS = SUCCESS
 
 # TODO(harlowja): use when we can timeout tasks??
 TIMED_OUT = 'TIMED_OUT'
@@ -122,3 +123,51 @@ def check_flow_transition(old_state, new_state):
         return True
     raise exc.InvalidStateException(
         "Flow transition from %s to %s is not allowed" % pair)
+
+
+## Task state transitions
+# https://wiki.openstack.org/wiki/TaskFlow/States_of_Task_and_Flow#Task_States
+
+_ALLOWED_TASK_TRANSITIONS = [
+    (PENDING, RUNNING),       # run it!
+
+    (RUNNING, SUCCESS),       # the task finished successfully
+    (RUNNING, FAILURE),       # the task failed
+
+    (FAILURE, REVERTING),     # task failed, do cleanup now
+    (SUCCESS, REVERTING),     # some other task failed, do cleanup now
+
+    (REVERTING, REVERTED),    # revert done
+    (REVERTING, FAILURE),     # revert failed
+
+    (REVERTED, PENDING),      # try again
+]
+_ALLOWED_TASK_TRANSITIONS.extend(
+    # NOTE(harlowja): the task was 'killed' while in one of the below 'a'
+    # states and it is permissible to let the task to start running or
+    # reverting immediately
+    (a, b)
+    for a in (REVERTED, REVERTING, RUNNING)
+    for b in (RUNNING, REVERTING)
+    if a != b
+)
+_ALLOWED_TASK_TRANSITIONS = frozenset(_ALLOWED_TASK_TRANSITIONS)
+
+
+def check_task_transition(old_state, new_state):
+    """Check that task can transition from old_state to new_state.
+
+    If transition can be performed, it returns True. If transition
+    should be ignored, it returns False. If transition is not
+    valid, it raises InvalidStateException.
+    """
+    if old_state == new_state:
+        return False
+    pair = (old_state, new_state)
+    if pair in _ALLOWED_TASK_TRANSITIONS:
+        return True
+    # TODO(harlowja): Should we check/allow for 3rd party states to be
+    # triggered during RUNNING by having a concept of a sub-state that we also
+    # verify against??
+    raise exc.InvalidStateException(
+        "Task transition from %s to %s is not allowed" % pair)
diff --git a/tools/state_graph.py b/tools/state_graph.py
index 838490d1..35298e2d 100644
--- a/tools/state_graph.py
+++ b/tools/state_graph.py
@@ -49,9 +49,17 @@ def main():
     parser.add_option("-f", "--file", dest="filename",
                       help="write svg to FILE", metavar="FILE",
                       default="states.svg")
+    parser.add_option("-t", "--tasks", dest="tasks",
+                      action='store_true',
+                      help="use task state transitions",
+                      default=False)
     (options, args) = parser.parse_args()
     g = nx.DiGraph(name="State transitions")
-    for (u, v) in states._ALLOWED_FLOW_TRANSITIONS:
+    if not options.tasks:
+        source = states._ALLOWED_FLOW_TRANSITIONS
+    else:
+        source = states._ALLOWED_TASK_TRANSITIONS
+    for (u, v) in source:
         if not g.has_node(u):
             g.add_node(u)
         if not g.has_node(v):