Source code for taskflow.conductors.base

# -*- coding: utf-8 -*-

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#    a copy of the License at
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#         http://www.apache.org/licenses/LICENSE-2.0
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#    Unless required by applicable law or agreed to in writing, software
#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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import abc
import os
import threading

import fasteners

from taskflow import engines
from taskflow import exceptions as excp
from taskflow.types import entity
from taskflow.types import notifier
from taskflow.utils import misc


[docs] class Conductor(object, metaclass=abc.ABCMeta): """Base for all conductor implementations. Conductors act as entities which extract jobs from a jobboard, assign there work to some engine (using some desired configuration) and then wait for that work to complete. If the work fails then they abandon the claimed work (or if the process they are running in crashes or dies this abandonment happens automatically) and then another conductor at a later period of time will finish up the prior failed conductors work. """ #: Entity kind used when creating new entity objects ENTITY_KIND = 'conductor' def __init__(self, name, jobboard, persistence=None, engine=None, engine_options=None): self._name = name self._jobboard = jobboard self._engine = engine self._engine_options = misc.safe_copy_dict(engine_options) self._persistence = persistence self._lock = threading.RLock() self._notifier = notifier.Notifier() @misc.cachedproperty def conductor(self): """Entity object that represents this conductor.""" hostname = misc.get_hostname() pid = os.getpid() name = '@'.join([self._name, hostname + ":" + str(pid)]) metadata = { 'hostname': hostname, 'pid': pid, } return entity.Entity(self.ENTITY_KIND, name, metadata) @property def notifier(self): """The conductor actions (or other state changes) notifier. NOTE(harlowja): different conductor implementations may emit different events + event details at different times, so refer to your conductor documentation to know exactly what can and what can not be subscribed to. """ return self._notifier def _flow_detail_from_job(self, job): """Extracts a flow detail from a job (via some manner). The current mechanism to accomplish this is the following choices: * If the job details provide a 'flow_uuid' key attempt to load this key from the jobs book and use that as the flow_detail to run. * If the job details does not have have a 'flow_uuid' key then attempt to examine the size of the book and if it's only one element in the book (aka one flow_detail) then just use that. * Otherwise if there is no 'flow_uuid' defined or there are > 1 flow_details in the book raise an error that corresponds to being unable to locate the correct flow_detail to run. """ book = job.book if book is None: raise excp.NotFound("No book found in job") if job.details and 'flow_uuid' in job.details: flow_uuid = job.details["flow_uuid"] flow_detail = book.find(flow_uuid) if flow_detail is None: raise excp.NotFound("No matching flow detail found in" " jobs book for flow detail" " with uuid %s" % flow_uuid) else: choices = len(book) if choices == 1: flow_detail = list(book)[0] elif choices == 0: raise excp.NotFound("No flow detail(s) found in jobs book") else: raise excp.MultipleChoices("No matching flow detail found (%s" " choices) in jobs book" % choices) return flow_detail def _engine_from_job(self, job): """Extracts an engine from a job (via some manner).""" flow_detail = self._flow_detail_from_job(job) store = {} if flow_detail.meta and 'store' in flow_detail.meta: store.update(flow_detail.meta['store']) if job.details and 'store' in job.details: store.update(job.details["store"]) engine = engines.load_from_detail(flow_detail, store=store, engine=self._engine, backend=self._persistence, **self._engine_options) return engine def _listeners_from_job(self, job, engine): """Returns a list of listeners to be attached to an engine. This method should be overridden in order to attach listeners to engines. It will be called once for each job, and the list returned listeners will be added to the engine for this job. :param job: A job instance that is about to be run in an engine. :param engine: The engine that listeners will be attached to. :returns: a list of (unregistered) listener instances. """ # TODO(dkrause): Create a standard way to pass listeners or # listener factories over the jobboard return []
[docs] @fasteners.locked def connect(self): """Ensures the jobboard is connected (noop if it is already).""" if not self._jobboard.connected: self._jobboard.connect()
[docs] @fasteners.locked def close(self): """Closes the contained jobboard, disallowing further use.""" self._jobboard.close()
[docs] @abc.abstractmethod def run(self, max_dispatches=None): """Continuously claims, runs, and consumes jobs (and repeat). :param max_dispatches: An upper bound on the number of jobs that will be dispatched, if none or negative this implies there is no limit to the number of jobs that will be dispatched, otherwise if positive this run method will return when that amount of jobs has been dispatched (instead of running forever and/or until stopped). """
@abc.abstractmethod def _dispatch_job(self, job): """Dispatches a claimed job for work completion. Accepts a single (already claimed) job and causes it to be run in an engine. Returns a future object that represented the work to be completed sometime in the future. The future should return a single boolean from its result() method. This boolean determines whether the job will be consumed (true) or whether it should be abandoned (false). :param job: A job instance that has already been claimed by the jobboard. """