147 lines
5.0 KiB
Python
147 lines
5.0 KiB
Python
# Copyright 2014 - Mirantis, Inc.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain 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,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import networkx as nx
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from networkx.algorithms import traversal
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from mistral.engine1 import commands
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from mistral import exceptions as exc
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from mistral.workflow import base
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from mistral.workflow import states
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class ReverseWorkflowHandler(base.WorkflowHandler):
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"""'Reverse workflow' handler.
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This handler implements the workflow pattern which is based on
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dependencies between tasks, i.e. each task in a workflow graph
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may be dependent on other tasks. To run this type of workflow
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user must specify a task name that serves a target node in the
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graph that the algorithm should come to by resolving all
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dependencies.
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For example, if there's a workflow consisting of two tasks
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'A' and 'B' where 'A' depends on 'B' and if we specify a target
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task name 'A' then the handler first will run task 'B' and then,
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when a dependency of 'A' is resolved, will run task 'A'.
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"""
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def start_workflow(self, **params):
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task_name = params.get('task_name')
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task_spec = self.wf_spec.get_tasks().get(task_name)
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if not task_spec:
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msg = 'Invalid task name [wf_spec=%s, task_name=%s]' % \
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(self.wf_spec, task_name)
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raise exc.WorkflowException(msg)
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task_specs = self._find_tasks_without_dependencies(task_spec)
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if len(task_specs) > 0:
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self._set_execution_state(states.RUNNING)
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return [commands.RunTask(t_s) for t_s in task_specs]
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def get_upstream_tasks(self, task_spec):
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return [self.wf_spec.get_tasks()[t_name]
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for t_name in task_spec.get_requires() or []]
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def _find_next_commands(self, task_db):
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"""Finds all tasks with resolved dependencies and return them
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in the form of engine commands.
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:param task_db: Task DB model causing the operation.
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:return: Tasks with resolved dependencies.
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"""
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# If cause task is the target task of the workflow then
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# there's no more tasks to start.
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if self.exec_db.start_params['task_name'] == task_db.name:
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return []
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# We need to analyse the graph and see which tasks are ready to start.
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resolved_task_specs = []
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success_task_names = set()
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for t in self.exec_db.tasks:
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if t.state == states.SUCCESS:
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success_task_names.add(t.name)
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for t_spec in self.wf_spec.get_tasks():
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# Skip task if it doesn't have a direct dependency
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# on the cause task.
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if task_db.name not in t_spec.get_requires():
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continue
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if not (set(t_spec.get_requires()) - success_task_names):
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t_db = self._find_db_task(t_spec.get_name())
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if not t_db or t_db.state == states.IDLE:
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resolved_task_specs.append(t_spec)
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return [commands.RunTask(t_s) for t_s in resolved_task_specs]
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def _find_tasks_without_dependencies(self, task_spec):
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"""Given a target task name finds tasks with no dependencies.
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:param task_spec: Target task specification in the workflow graph
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that dependencies are unwound from.
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:return: Tasks with no dependencies.
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"""
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tasks_spec = self.wf_spec.get_tasks()
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graph = self._build_graph(tasks_spec)
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# Unwind tasks from the target task
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# and filter out tasks with dependencies.
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return [
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t_spec for t_spec in
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traversal.dfs_postorder_nodes(graph.reverse(), task_spec)
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if not t_spec.get_requires()
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]
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def _build_graph(self, tasks_spec):
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graph = nx.DiGraph()
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# Add graph nodes.
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for t in tasks_spec:
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graph.add_node(t)
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# Add graph edges.
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for t_spec in tasks_spec:
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for dep_t_spec in self._get_dependency_tasks(tasks_spec, t_spec):
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graph.add_edge(dep_t_spec, t_spec)
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return graph
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def _get_dependency_tasks(self, tasks_spec, task_spec):
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dep_task_names = tasks_spec[task_spec.get_name()].get_requires()
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if len(dep_task_names) == 0:
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return []
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dep_t_specs = set()
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for t_spec in tasks_spec:
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for t_name in dep_task_names:
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if t_name == t_spec.get_name():
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dep_t_specs.add(t_spec)
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return dep_t_specs
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def _find_db_task(self, name):
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db_tasks = filter(lambda t: t.name == name, self.exec_db.tasks)
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return db_tasks[0] if db_tasks else None
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