153 lines
6.6 KiB
Python
153 lines
6.6 KiB
Python
# -*- coding: utf-8 -*-
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# vim: tabstop=4 shiftwidth=4 softtabstop=4
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# Copyright (C) 2012 Yahoo! Inc. All Rights Reserved.
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#
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# Licensed under the Apache License, Version 2.0 (the "License"); you may
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# not use this file except in compliance with the License. You may obtain
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# a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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# License for the specific language governing permissions and limitations
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# under the License.
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import collections as dict_provider
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import copy
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import functools
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import logging
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from taskflow.openstack.common import excutils
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from taskflow import exceptions as exc
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from taskflow import states
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LOG = logging.getLogger(__name__)
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class Workflow(object):
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"""A linear chain of independent tasks that can be applied as one unit or
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rolled back as one unit."""
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def __init__(self, name, tolerant=False, parents=None):
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# The tasks which have been applied will be collected here so that they
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# can be reverted in the correct order on failure.
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self._reversions = []
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self.name = name
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# If this chain can ignore individual task reversion failure then this
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# should be set to true, instead of the default value of false.
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self.tolerant = tolerant
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# Tasks and there results are stored here...
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self.tasks = []
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self.results = []
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# If this workflow has a parent workflow/s which need to be reverted if
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# this workflow fails then please include them here to allow this child
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# to call the parents...
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self.parents = parents
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# This should be a functor that returns whether a given task has
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# already ran by returning a pair of (has_result, result).
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#
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# NOTE(harlowja): This allows for resumption by skipping tasks which
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# have already occurred. The previous return value is needed due to
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# the contract we have with tasks that they will be given the value
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# they returned if reversion is triggered.
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self.result_fetcher = None
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# Any objects that want to listen when a task starts/stops/completes
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# or errors should be registered here. This can be used to monitor
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# progress and record tasks finishing (so that it becomes possible to
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# store the result of a task in some persistent or semi-persistent
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# storage backend).
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self.listeners = []
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# The state of this flow.
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self.state = states.PENDING
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def __str__(self):
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return "%s: %s" % (self.__class__.__name__, id(self))
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def run(self, context, *args, **kwargs):
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if self.state != states.PENDING:
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raise exc.InvalidStateException("Unable to run linear flow when "
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"in state %s" % (self.state))
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if self.result_fetcher:
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result_fetcher = functools.partial(self.result_fetcher, context)
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else:
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result_fetcher = None
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self.state = states.STARTED
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for task in self.tasks:
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try:
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# See if we have already ran this.
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result = None
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has_result = False
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if result_fetcher:
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(has_result, result) = result_fetcher(context, self, task)
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if not has_result:
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self.state = state.RUNNING
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else:
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self.state = state.RESUMING
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self._on_task_start(context, task)
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if not has_result:
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result = task.apply(context, *args, **kwargs)
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# Keep a pristine copy of the result
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# so that if said result is altered by other further states
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# the one here will not be. This ensures that if rollback
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# occurs that the task gets exactly the result it returned
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# and not a modified one.
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self.results.append((task, copy.deepcopy(result)))
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self._on_task_finish(context, task, result)
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except Exception as ex:
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self.state = states.FAILURE
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with excutils.save_and_reraise_exception():
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try:
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self._on_task_error(context, task)
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except Exception:
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LOG.exception("Dropping exception catched when"
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" notifying about existing task"
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" exception.")
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self.state = states.REVERTING
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self.rollback(context, exc.TaskException(task, self, ex))
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self.state = states.FAILURE
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# Only gets here if everything went successfully.
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self.state = states.SUCCESS
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def _on_task_error(self, context, task):
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# Notify any listeners that the task has errored.
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for i in self.listeners:
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i.notify(context, states.FAILURE, self, task)
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def _on_task_start(self, context, task):
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# Notify any listeners that we are about to start the given task.
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for i in self.listeners:
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i.notify(context, states.STARTED, self, task)
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def _on_task_finish(self, context, task, result):
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# Notify any listeners that we are finishing the given task.
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self._reversions.append((task, result))
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for i in self.listeners:
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i.notify(context, states.SUCCESS, self, task, result=result)
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def rollback(self, context, cause):
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for (i, (task, result)) in enumerate(reversed(self._reversions)):
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try:
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task.revert(context, result, cause)
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except Exception:
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# Ex: WARN: Failed rolling back stage 1 (validate_request) of
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# chain validation due to Y exception.
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msg = ("Failed rolling back stage %(index)s (%(task)s)"
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" of workflow %(workflow)s, due to inner exception.")
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LOG.warn(msg % {'index': (i + 1), 'task': task,
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'workflow': self})
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if not self.tolerant:
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# NOTE(harlowja): LOG a msg AND re-raise the exception if
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# the chain does not tolerate exceptions happening in the
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# rollback method.
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raise
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if self.parents:
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# Rollback any parents workflows if they exist...
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for p in self.parents:
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p.rollback(context, cause)
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