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# -*- coding: utf-8 -*-
# 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
from taskflow.types import notifier
from taskflow.utils import misc
class Engine(object, metaclass=abc.ABCMeta):
"""Base for all engines implementations.
:ivar Engine.notifier: A notification object that will dispatch
events that occur related to the flow the engine
contains.
:ivar atom_notifier: A notification object that will dispatch events that
occur related to the atoms the engine contains.
"""
def __init__(self, flow, flow_detail, backend, options):
self._flow = flow
self._flow_detail = flow_detail
self._backend = backend
self._options = misc.safe_copy_dict(options)
self._notifier = notifier.Notifier()
self._atom_notifier = notifier.Notifier()
@property
def notifier(self):
"""The flow notifier."""
return self._notifier
@property
def atom_notifier(self):
"""The atom notifier."""
return self._atom_notifier
@property
def options(self):
"""The options that were passed to this engine on construction."""
return self._options
@abc.abstractproperty
def storage(self):
"""The storage unit for this engine."""
@abc.abstractproperty
def statistics(self):
"""A dictionary of runtime statistics this engine has gathered.
This dictionary will be empty when the engine has never been
ran. When it is running or has ran previously it should have (but
may not) have useful and/or informational keys and values when
running is underway and/or completed.
.. warning:: The keys in this dictionary **should** be some what
stable (not changing), but there existence **may**
change between major releases as new statistics are
gathered or removed so before accessing keys ensure that
they actually exist and handle when they do not.
"""
@abc.abstractmethod
def compile(self):
"""Compiles the contained flow into a internal representation.
This internal representation is what the engine will *actually* use to
run. If this compilation can not be accomplished then an exception
is expected to be thrown with a message indicating why the compilation
could not be achieved.
"""
@abc.abstractmethod
def reset(self):
"""Reset back to the ``PENDING`` state.
If a flow had previously ended up (from a prior engine
:py:func:`.run`) in the ``FAILURE``, ``SUCCESS`` or ``REVERTED``
states (or for some reason it ended up in an intermediary state) it
can be desirable to make it possible to run it again. Calling this
method enables that to occur (without causing a state transition
failure, which would typically occur if :py:meth:`.run` is called
directly without doing a reset).
"""
@abc.abstractmethod
def prepare(self):
"""Performs any pre-run, but post-compilation actions.
NOTE(harlowja): During preparation it is currently assumed that the
underlying storage will be initialized, the atoms will be reset and
the engine will enter the ``PENDING`` state.
"""
@abc.abstractmethod
def validate(self):
"""Performs any pre-run, post-prepare validation actions.
NOTE(harlowja): During validation all final dependencies
will be verified and ensured. This will by default check that all
atoms have satisfiable requirements (satisfied by some other
provider).
"""
@abc.abstractmethod
def run(self):
"""Runs the flow in the engine to completion (or die trying)."""
@abc.abstractmethod
def suspend(self):
"""Attempts to suspend the engine.
If the engine is currently running atoms then this will attempt to
suspend future work from being started (currently active atoms can
not currently be preempted) and move the engine into a suspend state
which can then later be resumed from.
"""
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