81d0884d55
Its useful to be able to check if a flow contains anything by just inspecting the len() of the flow. This can be used to avoid running a flow in the first place if nothing is in said flow. Change-Id: Ibfea7f10fc67d5dd3ddfa6f6fe6c08805562998a
283 lines
11 KiB
Python
283 lines
11 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
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import copy
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import logging
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from taskflow.openstack.common import excutils
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from taskflow import decorators
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from taskflow import exceptions as exc
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from taskflow import states
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from taskflow import utils
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from taskflow.patterns import base
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LOG = logging.getLogger(__name__)
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class Flow(base.Flow):
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""""A linear chain of tasks that can be applied in order as one unit and
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rolled back as one unit using the reverse order that the tasks have
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been applied in.
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Note(harlowja): Each task in the chain must have requirements
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which are satisfied by the previous task/s in the chain."""
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def __init__(self, name, parents=None, uuid=None):
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super(Flow, self).__init__(name, parents, uuid)
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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._accumulator = utils.RollbackAccumulator()
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# Tasks results are stored here. Lookup is by the uuid that was
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# returned from the add function.
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self.results = {}
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# The previously left off iterator that can be used to resume from
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# the last task (if interrupted and soft-reset).
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self._leftoff_at = None
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# All runners to run are collected here.
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self._runners = []
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self._connected = False
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# The resumption strategy to use.
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self.resumer = None
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@decorators.locked
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def add(self, task):
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"""Adds a given task to this flow."""
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assert isinstance(task, collections.Callable)
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r = utils.Runner(task)
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r.runs_before = list(reversed(self._runners))
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self._runners.append(r)
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self._reset_internals()
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return r.uuid
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def _reset_internals(self):
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self._connected = False
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self._leftoff_at = None
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def _associate_providers(self, runner):
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# Ensure that some previous task provides this input.
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who_provides = {}
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task_requires = runner.requires
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LOG.debug("Finding providers of %s for %s", task_requires, runner)
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for r in task_requires:
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provider = None
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for before_me in runner.runs_before:
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if r in before_me.provides:
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provider = before_me
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break
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if provider:
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LOG.debug("Found provider of %s from %s", r, provider)
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who_provides[r] = provider
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# Ensure that the last task provides all the needed input for this
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# task to run correctly.
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missing_requires = task_requires - set(who_provides.keys())
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if missing_requires:
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raise exc.MissingDependencies(runner, sorted(missing_requires))
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runner.providers.update(who_provides)
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def __str__(self):
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lines = ["LinearFlow: %s" % (self.name)]
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lines.append("%s" % (self.uuid))
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lines.append("%s" % (len(self._runners)))
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lines.append("%s" % (len(self.parents)))
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lines.append("%s" % (self.state))
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return "; ".join(lines)
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@decorators.locked
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def remove(self, uuid):
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index_removed = -1
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for (i, r) in enumerate(self._runners):
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if r.uuid == uuid:
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index_removed = i
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break
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if index_removed == -1:
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raise ValueError("No runner found with uuid %s" % (uuid))
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else:
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removed = self._runners.pop(index_removed)
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self._reset_internals()
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# Go and remove it from any runner after the removed runner since
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# those runners may have had an attachment to it.
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for r in self._runners[index_removed:]:
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try:
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r.runs_before.remove(removed)
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except (IndexError, ValueError):
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pass
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def __len__(self):
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return len(self._runners)
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def _connect(self):
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if self._connected:
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return self._runners
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for r in self._runners:
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r.providers = {}
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for r in reversed(self._runners):
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self._associate_providers(r)
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self._connected = True
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return self._runners
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def _ordering(self):
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return iter(self._connect())
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@decorators.locked
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def run(self, context, *args, **kwargs):
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super(Flow, self).run(context, *args, **kwargs)
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def resume_it():
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if self._leftoff_at is not None:
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return ([], self._leftoff_at)
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if self.resumer:
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(finished, leftover) = self.resumer.resume(self,
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self._ordering())
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else:
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finished = []
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leftover = self._ordering()
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return (finished, leftover)
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self._change_state(context, states.STARTED)
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try:
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those_finished, leftover = resume_it()
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except Exception:
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with excutils.save_and_reraise_exception():
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self._change_state(context, states.FAILURE)
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def run_it(runner, failed=False, result=None, simulate_run=False):
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try:
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# Add the task to be rolled back *immediately* so that even if
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# the task fails while producing results it will be given a
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# chance to rollback.
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rb = utils.RollbackTask(context, runner.task, result=None)
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self._accumulator.add(rb)
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self.task_notifier.notify(states.STARTED, details={
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'context': context,
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'flow': self,
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'runner': runner,
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})
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if not simulate_run:
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result = runner(context, *args, **kwargs)
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else:
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if failed:
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# TODO(harlowja): make this configurable??
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# If we previously failed, we want to fail again at
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# the same place.
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if not result:
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# If no exception or exception message was provided
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# or captured from the previous run then we need to
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# form one for this task.
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result = "%s failed running." % (runner.task)
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if isinstance(result, basestring):
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result = exc.InvalidStateException(result)
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if not isinstance(result, Exception):
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LOG.warn("Can not raise a non-exception"
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" object: %s", result)
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result = exc.InvalidStateException()
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raise result
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# Adjust the task result in the accumulator before
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# notifying others that the task has finished to
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# avoid the case where a listener might throw an
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# exception.
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#
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# Note(harlowja): Keep the original result in the
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# accumulator only and give a duplicated copy to
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# avoid the original result being altered by other
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# tasks.
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#
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# This is due to python being by reference (which means
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# some task could alter this result intentionally or not
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# intentionally).
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rb.result = result
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runner.result = result
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self.results[runner.uuid] = copy.deepcopy(result)
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self.task_notifier.notify(states.SUCCESS, details={
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'context': context,
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'flow': self,
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'runner': runner,
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})
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except Exception as e:
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runner.result = e
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cause = utils.FlowFailure(runner, self, e)
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with excutils.save_and_reraise_exception():
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# Notify any listeners that the task has errored.
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self.task_notifier.notify(states.FAILURE, details={
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'context': context,
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'flow': self,
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'runner': runner,
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})
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self.rollback(context, cause)
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if len(those_finished):
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self._change_state(context, states.RESUMING)
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for (r, details) in those_finished:
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# Fake running the task so that we trigger the same
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# notifications and state changes (and rollback that
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# would have happened in a normal flow).
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failed = states.FAILURE in details.get('states', [])
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result = details.get('result')
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run_it(r, failed=failed, result=result, simulate_run=True)
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self._leftoff_at = leftover
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self._change_state(context, states.RUNNING)
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if self.state == states.INTERRUPTED:
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return
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was_interrupted = False
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for r in leftover:
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r.reset()
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run_it(r)
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if self.state == states.INTERRUPTED:
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was_interrupted = True
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break
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if not was_interrupted:
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# Only gets here if everything went successfully.
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self._change_state(context, states.SUCCESS)
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self._leftoff_at = None
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@decorators.locked
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def reset(self):
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super(Flow, self).reset()
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self.results = {}
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self.resumer = None
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self._accumulator.reset()
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self._reset_internals()
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@decorators.locked
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def rollback(self, context, cause):
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# Performs basic task by task rollback by going through the reverse
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# order that tasks have finished and asking said task to undo whatever
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# it has done. If this flow has any parent flows then they will
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# also be called to rollback any tasks said parents contain.
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#
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# Note(harlowja): if a flow can more simply revert a whole set of
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# tasks via a simpler command then it can override this method to
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# accomplish that.
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#
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# For example, if each task was creating a file in a directory, then
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# it's easier to just remove the directory than to ask each task to
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# delete its file individually.
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self._change_state(context, states.REVERTING)
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try:
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self._accumulator.rollback(cause)
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finally:
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self._change_state(context, states.FAILURE)
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# Rollback any parents flows if they exist...
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for p in self.parents:
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p.rollback(context, cause)
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