From 135f562408e8baa81016da9ac55ea40eda174757 Mon Sep 17 00:00:00 2001
From: Joshua Harlow <harlowja@yahoo-inc.com>
Date: Mon, 30 Dec 2013 18:04:08 -0800
Subject: [PATCH] Move autobinding to task base class

The autobinding functionality is more of a
general task function so it is nice to have it
available for use in the root base class instead
of being an auxilary method.

Change-Id: I75abed25cb0bf165f61f8317e3cb1a62a3f9bf4a
---
 taskflow/engines/action_engine/executor.py | 30 ++++++----------------
 taskflow/task.py                           | 21 +++++++++++++++
 2 files changed, 29 insertions(+), 22 deletions(-)

diff --git a/taskflow/engines/action_engine/executor.py b/taskflow/engines/action_engine/executor.py
index 47a195d1c..66897a664 100644
--- a/taskflow/engines/action_engine/executor.py
+++ b/taskflow/engines/action_engine/executor.py
@@ -17,7 +17,6 @@
 #    under the License.
 
 import abc
-import contextlib
 
 from concurrent import futures
 import six
@@ -31,21 +30,8 @@ EXECUTED = 'executed'
 REVERTED = 'reverted'
 
 
-@contextlib.contextmanager
-def _autobind(task, bind_name, bind_func, **kwargs):
-    task.bind(bind_name, bind_func, **kwargs)
-    try:
-        yield task
-    finally:
-        task.unbind(bind_name, bind_func)
-
-
-def _noop(*args, **kwargs):
-    pass
-
-
 def _execute_task(task, arguments, progress_callback):
-    with _autobind(task, 'update_progress', progress_callback):
+    with task.autobind('update_progress', progress_callback):
         try:
             result = task.execute(**arguments)
         except Exception:
@@ -59,7 +45,7 @@ def _revert_task(task, arguments, result, failures, progress_callback):
     kwargs = arguments.copy()
     kwargs['result'] = result
     kwargs['flow_failures'] = failures
-    with _autobind(task, 'update_progress', progress_callback):
+    with task.autobind('update_progress', progress_callback):
         try:
             result = task.revert(**kwargs)
         except Exception:
@@ -79,12 +65,12 @@ class TaskExecutorBase(object):
     """
 
     @abc.abstractmethod
-    def execute_task(self, task, arguments, progress_callback=_noop):
+    def execute_task(self, task, arguments, progress_callback=None):
         """Schedules task execution."""
 
     @abc.abstractmethod
     def revert_task(self, task, arguments, result, failures,
-                    progress_callback=_noop):
+                    progress_callback=None):
         """Schedules task reversion"""
 
     @abc.abstractmethod
@@ -103,12 +89,12 @@ class TaskExecutorBase(object):
 class SerialTaskExecutor(TaskExecutorBase):
     """Execute task one after another."""
 
-    def execute_task(self, task, arguments, progress_callback=_noop):
+    def execute_task(self, task, arguments, progress_callback=None):
         return async_utils.make_completed_future(
             _execute_task(task, arguments, progress_callback))
 
     def revert_task(self, task, arguments, result, failures,
-                    progress_callback=_noop):
+                    progress_callback=None):
         return async_utils.make_completed_future(
             _revert_task(task, arguments, result,
                          failures, progress_callback))
@@ -129,12 +115,12 @@ class ParallelTaskExecutor(TaskExecutorBase):
         self._executor = executor
         self._own_executor = executor is None
 
-    def execute_task(self, task, arguments, progress_callback=_noop):
+    def execute_task(self, task, arguments, progress_callback=None):
         return self._executor.submit(
             _execute_task, task, arguments, progress_callback)
 
     def revert_task(self, task, arguments, result, failures,
-                    progress_callback=_noop):
+                    progress_callback=None):
         return self._executor.submit(
             _revert_task, task,
             arguments, result, failures, progress_callback)
diff --git a/taskflow/task.py b/taskflow/task.py
index ccc8d95c2..88bcec04e 100644
--- a/taskflow/task.py
+++ b/taskflow/task.py
@@ -19,6 +19,7 @@
 
 import abc
 import collections
+import contextlib
 import logging
 
 import six
@@ -189,6 +190,26 @@ class BaseTask(object):
                 LOG.exception("Failed calling `%s` on event '%s'",
                               reflection.get_callable_name(handler), event)
 
+    @contextlib.contextmanager
+    def autobind(self, event_name, handler_func, **kwargs):
+        """Binds a given function to the task for a given event name and then
+        unbinds that event name and associated function automatically on exit.
+        """
+        bound = False
+        if handler_func is not None:
+            try:
+                self.bind(event_name, handler_func, **kwargs)
+                bound = True
+            except ValueError:
+                LOG.exception("Failed binding functor `%s` as a reciever of"
+                              " event '%s' notifications emitted from task %s",
+                              handler_func, event_name, self)
+        try:
+            yield self
+        finally:
+            if bound:
+                self.unbind(event_name, handler_func)
+
     def bind(self, event, handler, **kwargs):
         """Attach a handler to an event for the task.