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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 json
import logging
import os
import sys
import time
logging.basicConfig(level=logging.ERROR)
top_dir = os.path.abspath(os.path.join(os.path.dirname(__file__),
os.pardir,
os.pardir))
sys.path.insert(0, top_dir)
from oslo_utils import uuidutils
from taskflow import engines
from taskflow.listeners import printing
from taskflow.patterns import graph_flow as gf
from taskflow.patterns import linear_flow as lf
from taskflow import task
from taskflow.utils import misc
# INTRO: This example walks through a miniature workflow which simulates
# the reception of an API request, creation of a database entry, driver
# activation (which invokes a 'fake' webservice) and final completion.
#
# This example also shows how a function/object (in this class the url sending)
# that occurs during driver activation can update the progress of a task
# without being aware of the internals of how to do this by associating a
# callback that the url sending can update as the sending progresses from 0.0%
# complete to 100% complete.
class DB(object):
def query(self, sql):
print("Querying with: %s" % (sql))
class UrlCaller(object):
def __init__(self):
self._send_time = 0.5
self._chunks = 25
def send(self, url, data, status_cb=None):
sleep_time = float(self._send_time) / self._chunks
for i in range(0, len(data)):
time.sleep(sleep_time)
# As we send the data, each chunk we 'fake' send will progress
# the sending progress that much further to 100%.
if status_cb:
status_cb(float(i) / len(data))
# Since engines save the output of tasks to a optional persistent storage
# backend resources have to be dealt with in a slightly different manner since
# resources are transient and can *not* be persisted (or serialized). For tasks
# that require access to a set of resources it is a common pattern to provide
# a object (in this case this object) on construction of those tasks via the
# task constructor.
class ResourceFetcher(object):
def __init__(self):
self._db_handle = None
self._url_handle = None
@property
def db_handle(self):
if self._db_handle is None:
self._db_handle = DB()
return self._db_handle
@property
def url_handle(self):
if self._url_handle is None:
self._url_handle = UrlCaller()
return self._url_handle
class ExtractInputRequest(task.Task):
def __init__(self, resources):
super(ExtractInputRequest, self).__init__(provides="parsed_request")
self._resources = resources
def execute(self, request):
return {
'user': request.user,
'user_id': misc.as_int(request.id),
'request_id': uuidutils.generate_uuid(),
}
class MakeDBEntry(task.Task):
def __init__(self, resources):
super(MakeDBEntry, self).__init__()
self._resources = resources
def execute(self, parsed_request):
db_handle = self._resources.db_handle
db_handle.query("INSERT %s INTO mydb" % (parsed_request))
def revert(self, result, parsed_request):
db_handle = self._resources.db_handle
db_handle.query("DELETE %s FROM mydb IF EXISTS" % (parsed_request))
class ActivateDriver(task.Task):
def __init__(self, resources):
super(ActivateDriver, self).__init__(provides='sent_to')
self._resources = resources
self._url = "http://blahblah.com"
def execute(self, parsed_request):
print("Sending billing data to %s" % (self._url))
url_sender = self._resources.url_handle
# Note that here we attach our update_progress function (which is a
# function that the engine also 'binds' to) to the progress function
# that the url sending helper class uses. This allows the task progress
# to be tied to the url sending progress, which is very useful for
# downstream systems to be aware of what a task is doing at any time.
url_sender.send(self._url, json.dumps(parsed_request),
status_cb=self.update_progress)
return self._url
def update_progress(self, progress, **kwargs):
# Override the parent method to also print out the status.
super(ActivateDriver, self).update_progress(progress, **kwargs)
print("%s is %0.2f%% done" % (self.name, progress * 100))
class DeclareSuccess(task.Task):
def execute(self, sent_to):
print("Done!")
print("All data processed and sent to %s" % (sent_to))
class DummyUser(object):
def __init__(self, user, id_):
self.user = user
self.id = id_
# Resources (db handles and similar) of course can *not* be persisted so we
# need to make sure that we pass this resource fetcher to the tasks constructor
# so that the tasks have access to any needed resources (the resources are
# lazily loaded so that they are only created when they are used).
resources = ResourceFetcher()
flow = lf.Flow("initialize-me")
# 1. First we extract the api request into a usable format.
# 2. Then we go ahead and make a database entry for our request.
flow.add(ExtractInputRequest(resources), MakeDBEntry(resources))
# 3. Then we activate our payment method and finally declare success.
sub_flow = gf.Flow("after-initialize")
sub_flow.add(ActivateDriver(resources), DeclareSuccess())
flow.add(sub_flow)
# Initially populate the storage with the following request object,
# prepopulating this allows the tasks that dependent on the 'request' variable
# to start processing (in this case this is the ExtractInputRequest task).
store = {
'request': DummyUser(user="bob", id_="1.35"),
}
eng = engines.load(flow, engine='serial', store=store)
# This context manager automatically adds (and automatically removes) a
# helpful set of state transition notification printing helper utilities
# that show you exactly what transitions the engine is going through
# while running the various billing related tasks.
with printing.PrintingListener(eng):
eng.run()
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