Introduce TaskExecutor

This change introduces new entity in the ActionEngine internals,
TaskExecutor. It's responsibilities are simple: take task and it's
arguments and execute it or revert it when engine says so.

Implements blueprint task-executor
Change-Id: I81c63bf4f43342a630f5aa9872fb14776e481176

taskflow/engines/action_engine/engine.py

@@ -20,6 +20,7 @@ import threading
 
 from concurrent import futures
 
+from taskflow.engines.action_engine import executor
 from taskflow.engines.action_engine import graph_action
 from taskflow.engines.action_engine import task_action
 from taskflow.engines import base
@@ -51,6 +52,7 @@ class ActionEngine(base.EngineBase):
     """
     _graph_action_cls = None
     _task_action_cls = task_action.TaskAction
+    _task_executor_cls = executor.SerialTaskExecutor
 
     def __init__(self, flow, flow_detail, backend, conf):
         super(ActionEngine, self).__init__(flow, flow_detail, backend, conf)
@@ -59,7 +61,9 @@ class ActionEngine(base.EngineBase):
         self._state_lock = threading.RLock()
         self.notifier = misc.TransitionNotifier()
         self.task_notifier = misc.TransitionNotifier()
+        self._task_executor = self._task_executor_cls()
         self.task_action = self._task_action_cls(self.storage,
+                                                 self._task_executor,
                                                  self.task_notifier)
 
     def _revert(self, current_failure=None):
@@ -106,10 +110,14 @@ class ActionEngine(base.EngineBase):
         missing = self._flow.requires - external_provides
         if missing:
             raise exc.MissingDependencies(self._flow, sorted(missing))
+        self._task_executor.start()
+        try:
             if self.storage.has_failures():
                 self._revert()
             else:
                 self._run()
+        finally:
+            self._task_executor.stop()
 
     def _run(self):
         self._change_state(states.RUNNING)

taskflow/engines/action_engine/executor.py

@@ -0,0 +1,154 @@
+# -*- coding: utf-8 -*-
+
+# vim: tabstop=4 shiftwidth=4 softtabstop=4
+
+#    Copyright (C) 2013 Yahoo! Inc. All Rights Reserved.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+import abc
+import contextlib
+import six
+
+from concurrent import futures
+
+from taskflow.utils import misc
+from taskflow.utils import threading_utils
+
+
+@contextlib.contextmanager
+def _autobind(task, bind_name, bind_func, **kwargs):
+    try:
+        task.bind(bind_name, bind_func, **kwargs)
+        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):
+        try:
+            result = task.execute(**arguments)
+        except Exception:
+            # NOTE(imelnikov): wrap current exception with Failure
+            # object and return it
+            result = misc.Failure()
+    return task, 'executed', result
+
+
+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):
+        try:
+            result = task.revert(**kwargs)
+        except Exception:
+            # NOTE(imelnikov): wrap current exception with Failure
+            # object and return it
+            result = misc.Failure()
+    return task, 'reverted', result
+
+
+@six.add_metaclass(abc.ABCMeta)
+class TaskExecutorBase(object):
+    """Executes and reverts tasks.
+
+    This class takes task and its arguments and executes or reverts it.
+    It encapsulates knowledge on how task should be executed or reverted:
+    right now, on separate thread, on another machine, etc.
+    """
+
+    @abc.abstractmethod
+    def execute_task(self, task, arguments, progress_callback=_noop):
+        """Schedules task execution."""
+
+    @abc.abstractmethod
+    def revert_task(self, task, arguments, result, failures,
+                    progress_callback=_noop):
+        """Schedules task reversion"""
+
+    @abc.abstractmethod
+    def wait_for_any(self, fs):
+        """Wait for futures returned by this executor to complete"""
+
+    def start(self):
+        """Prepare to execute tasks"""
+        pass
+
+    def stop(self):
+        """Finalize task executor"""
+        pass
+
+
+class SerialTaskExecutor(TaskExecutorBase):
+    """Execute task one after another."""
+
+    @staticmethod
+    def _completed_future(result):
+        future = futures.Future()
+        future.set_result(result)
+        return future
+
+    def execute_task(self, task, arguments, progress_callback=_noop):
+        return self._completed_future(
+            _execute_task(task, arguments, progress_callback))
+
+    def revert_task(self, task, arguments, result, failures,
+                    progress_callback=_noop):
+        return self._completed_future(
+            _revert_task(task, arguments, result,
+                         failures, progress_callback))
+
+    def wait_for_any(self, fs):
+        # NOTE(imelnikov): this executor returns only done futures
+        return fs, []
+
+
+class ParallelTaskExecutor(TaskExecutorBase):
+    """Executes tasks in parallel.
+
+    Submits tasks to executor which should provide interface similar
+    to concurrent.Futures.Executor.
+    """
+
+    def __init__(self, executor=None):
+        self._executor = executor
+        self._own_executor = executor is None
+
+    def execute_task(self, task, arguments, progress_callback=_noop):
+        return self._executor.submit(
+            _execute_task, task, arguments, progress_callback)
+
+    def revert_task(self, task, arguments, result, failures,
+                    progress_callback=_noop):
+        return self._executor.submit(
+            _revert_task, task,
+            arguments, result, failures, progress_callback)
+
+    def wait_for_any(self, fs):
+        return futures.wait(fs, return_when=futures.FIRST_COMPLETED)
+
+    def start(self):
+        if self._own_executor:
+            thread_count = threading_utils.get_optimal_thread_count()
+            self._executor = futures.ThreadPoolExecutor(thread_count)
+
+    def stop(self):
+        if self._own_executor:
+            self._executor.shutdown(wait=True)
+            self._executor = None

taskflow/engines/action_engine/task_action.py

@@ -16,10 +16,8 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-import contextlib
 import logging
 
-from taskflow.openstack.common import excutils
 from taskflow import states
 from taskflow.utils import misc
 
@@ -28,18 +26,10 @@ LOG = logging.getLogger(__name__)
 SAVE_RESULT_STATES = (states.SUCCESS, states.FAILURE)
 
 
-@contextlib.contextmanager
-def _autobind(task, bind_name, bind_func, **kwargs):
-    try:
-        task.bind(bind_name, bind_func, **kwargs)
-        yield task
-    finally:
-        task.unbind(bind_name, bind_func)
-
-
 class TaskAction(object):
-    def __init__(self, storage, notifier):
+    def __init__(self, storage, task_executor, notifier):
         self._storage = storage
+        self._task_executor = task_executor
         self._notifier = notifier
 
     def _change_state(self, task, state, result=None, progress=None):
@@ -75,27 +65,29 @@ class TaskAction(object):
     def execute(self, task):
         if not self._change_state(task, states.RUNNING, progress=0.0):
             return
-        with _autobind(task, 'update_progress', self._on_update_progress):
-            try:
-                kwargs = self._storage.fetch_mapped_args(task.rebind)
-                result = task.execute(**kwargs)
-            except Exception:
-                failure = misc.Failure()
-                self._change_state(task, states.FAILURE, result=failure)
-                failure.reraise()
 
+        kwargs = self._storage.fetch_mapped_args(task.rebind)
+        future = self._task_executor.execute_task(task, kwargs,
+                                                  self._on_update_progress)
+        self._task_executor.wait_for_any(future)
+        _task, _event, result = future.result()
+        if isinstance(result, misc.Failure):
+            self._change_state(task, states.FAILURE, result=result)
+            result.reraise()
         self._change_state(task, states.SUCCESS, result=result, progress=1.0)
 
     def revert(self, task):
         if not self._change_state(task, states.REVERTING, progress=0.0):
             return
-        with _autobind(task, 'update_progress', self._on_update_progress):
         kwargs = self._storage.fetch_mapped_args(task.rebind)
-            kwargs['result'] = self._storage.get(task.name)
-            kwargs['flow_failures'] = self._storage.get_failures()
-            try:
-                task.revert(**kwargs)
-            except Exception:
-                with excutils.save_and_reraise_exception():
+        task_result = self._storage.get(task.name)
+        failures = self._storage.get_failures()
+        future = self._task_executor.revert_task(task, kwargs,
+                                                 task_result, failures,
+                                                 self._on_update_progress)
+        self._task_executor.wait_for_any(future)
+        _task, _event, result = future.result()
+        if isinstance(result, misc.Failure):
             self._change_state(task, states.FAILURE)
+            result.reraise()
         self._change_state(task, states.REVERTED, progress=1.0)