How to start another thread in request handling thread with Flask? - python-3.x

Question

First of all, I have tried looking for answers in this website. But no luck...
What I wanna achieve is that starting an independent thread in the request handling thread to do some asynchronous task. The tricky point is that there are some database operations needed in this independent thread.
Here is an example. Five files included.
project
|__manager.py
|__config.py
|__deployer
|__`__init__.py`
|__models.py
|__views.py
|__operators.py
Detail code below...
# deployer/__init__.py
from flask import Flask
from deployer.models import db
def create_app():
app = Flask(__name__)
app.config.from_object(object_name)
db.init_app(app)
# Add route for index
#app.route('/')
def index():
return {'code': 200, 'message': 'OK'}
return app
# manager.py
from os import environ
from flask_script import Manager, Server
from deployer import create_app
from flask_restful import Api
from deployer.views import HostView
env = environ.get('APM_ENV', 'dev')
app = create_app('config.%sConfig' % env.capitalize())
api = Api(app)
api.add_resource(HostView, '/api/v1/hosts')
manager = Manager(app)
manager.add_command("server", Server(host='0.0.0.0', port=9527))
if __name__ == '__main__':
manager.run(default_command='server')
# deployer/views.py
from flask_restful import Resource, reqparse
from flask import jsonify
from deployer.models import db, Host
from deployer.operators import HostInitiator
parser = reqparse.RequestParser()
parser.add_argument('host', type=int, help='Specify an unique host.')
class HostView(Resource):
def get(self):
h = db.session.query(Host).filter(Host.id == 1).one()
return jsonify(
host_id=h.id,
host_code=h.code,
host_ip=h.ip_addr_v4
)
def post(self):
h = Host(
code='Harbor',
ip_addr_v4='10.10.10.199',
state='created'
)
db.session.add(h)
db.session.commit()
initiator = HostInitiator(host=h)
initiator.start()
return {
'code': 'Harbor',
'ip_addr_v4': '10.10.10.199',
'state': 'created'
}
# deployer/models.py
from sqlalchemy import Column, Integer, String
from flask_sqlalchemy import SQLAlchemy
db = SQLAlchemy()
class Host(db.Model):
__tablename__ = 'br_host'
id = Column(Integer, primary_key=True, autoincrement=True)
code = Column(String(128), index=True, nullable=False)
ip_addr_v4 = Column(String(15), nullable=False)
state = Column(String(16), nullable=False)
# deployer/operators.py
from threading import Thread
from deployer.models import db
class HostInitiator(Thread):
def __init__(self, host):
super().__init__()
self.host = host
def run(self):
# Update Host.state [created-->initating]
db.session.query(Host).filter(Host.id == self.host.id).update({'state': 'initating'})
db.session.commit()
# do some initiating things...
# Update Host.state [initating-->ready]
db.session.query(Host).filter(Host.id == self.host.id).update({'state': 'ready'})
db.session.commit()
Always got outside application context error with code above. The error message indicates that no database operation is permitted in the HostInitiator thread.
It suggests me to push a context or move my code into a view function. I'm suffering this quite a while, please help out if you guys have any suggestions. Thanks in advance.

Answer 1

The code works for me
def test_multi_threading_query():
# module which i create Flask app instance
from app.main import app
# module which i create sqlalchemhy instance
from app.model.db import db, Post
with app.app_context():
posts = Post.query.all()
p = posts[0]
p.foo = 1
db.session.add(p)
db.session.commit()
print(p)
#api.route('/test')
def test_view():
from threading import Thread
t = Thread(target=test_multi_threading_query)
t.start()
return ''
# main.py
app = Flask(__main__)
#db.py
db = SQLAlchemy()
class Post(db.Model):
id = db.Column(db.Integer, primary_key=True)
foo = db.Column(db.Integer)
https://flask.palletsprojects.com/en/1.1.x/appcontext/