taskflow/taskflow/flow.py

135 lines
4.7 KiB
Python

# -*- coding: utf-8 -*-
# Copyright (C) 2012 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
from oslo_utils import reflection
# Link metadata keys that have inherent/special meaning.
#
# This key denotes the link is an invariant that ensures the order is
# correctly preserved.
LINK_INVARIANT = 'invariant'
# This key denotes the link is a manually/user-specified.
LINK_MANUAL = 'manual'
# This key denotes the link was created when resolving/compiling retries.
LINK_RETRY = 'retry'
# This key denotes the link was created due to symbol constraints and the
# value will be a set of names that the constraint ensures are satisfied.
LINK_REASONS = 'reasons'
#
# This key denotes a callable that will determine if the target is visited.
LINK_DECIDER = 'decider'
# Chop off full module names of patterns that are built-in to taskflow...
_CHOP_PAT = "taskflow.patterns."
_CHOP_PAT_LEN = len(_CHOP_PAT)
# This key denotes the depth the decider will apply (defaulting to all).
LINK_DECIDER_DEPTH = 'decider_depth'
class Flow(object, metaclass=abc.ABCMeta):
"""The base abstract class of all flow implementations.
A flow is a structure that defines relationships between tasks. You can
add tasks and other flows (as subflows) to the flow, and the flow provides
a way to implicitly or explicitly define how they are interdependent.
Exact structure of the relationships is defined by concrete
implementation, while this class defines common interface and adds
human-readable (not necessary unique) name.
NOTE(harlowja): if a flow is placed in another flow as a subflow, a desired
way to compose flows together, then it is valid and permissible that during
compilation the subflow & parent flow *may* be flattened into a new flow.
"""
def __init__(self, name, retry=None):
self._name = str(name)
self._retry = retry
# NOTE(akarpinska): if retry doesn't have a name,
# the name of its owner will be assigned
if self._retry is not None and self._retry.name is None:
self._retry.name = self.name + "_retry"
@property
def name(self):
"""A non-unique name for this flow (human readable)."""
return self._name
@property
def retry(self):
"""The associated flow retry controller.
This retry controller object will affect & control how (and if) this
flow and its contained components retry when execution is underway and
a failure occurs.
"""
return self._retry
@abc.abstractmethod
def add(self, *items):
"""Adds a given item/items to this flow."""
@abc.abstractmethod
def __len__(self):
"""Returns how many items are in this flow."""
@abc.abstractmethod
def __iter__(self):
"""Iterates over the children of the flow."""
@abc.abstractmethod
def iter_links(self):
"""Iterates over dependency links between children of the flow.
Iterates over 3-tuples ``(A, B, meta)``, where
* ``A`` is a child (atom or subflow) link starts from;
* ``B`` is a child (atom or subflow) link points to; it is
said that ``B`` depends on ``A`` or ``B`` requires ``A``;
* ``meta`` is link metadata, a dictionary.
"""
@abc.abstractmethod
def iter_nodes(self):
"""Iterate over nodes of the flow.
Iterates over 2-tuples ``(A, meta)``, where
* ``A`` is a child (atom or subflow) of current flow;
* ``meta`` is link metadata, a dictionary.
"""
def __str__(self):
cls_name = reflection.get_class_name(self)
if cls_name.startswith(_CHOP_PAT):
cls_name = cls_name[_CHOP_PAT_LEN:]
return '"%s: %s(len=%d)"' % (cls_name, self.name, len(self))
@property
def provides(self):
"""Set of symbol names provided by the flow."""
provides = set()
if self._retry is not None:
provides.update(self._retry.provides)
for item in self:
provides.update(item.provides)
return frozenset(provides)
@property
@abc.abstractmethod
def requires(self):
"""Set of *unsatisfied* symbol names required by the flow."""