with app.app_context() in thread: AttributeError: __enter__ about quart HOT 12 CLOSED

This is a common issue with Flask and Quart contexts, you can solve it via the copy_current_app_context decorator, as so,

Thread(
      target=copy_current_app_context(send_async_email),
      args=(current_app._get_current_object(), msg),
    ).start()

The issue is that the context (with Quart 0.7 onwards) is copied for you into different asyncio tasks, however it isn't copied into a different Thread. The explicit usage of the copy_current_app_context does so though.

from quart.

I am getting the following warning:

RuntimeWarning: coroutine 'wrapper' was never awaited
  self._target(*self._args, **self._kwargs)

The wrapped function does not run either.

from quart.

Ah yes as the copy_current_app_context returns a coroutine function rather than a function. You need to run an event loop on the other thread.

Are you trying to run a sync or async function in another thread? Also are you trying to invoke the thread from a sync or async context?

from quart.

Sync in the Thread as shown in the example above. I am invoking from an async context within one of the Quart_OpenAPI endpoints:

def send_email(_app, message):
    with _app.app_context():
        mail.send(message)

@app.route('/test')
class Test(Resource):
    async def get(self):
        message = Message(sender=app.config.get('MAIL_USERNAME'),
                          recipients=[app.config.get('MAIL_USERNAME')],
                          subject='TEST')

        Thread(
            target=copy_current_app_context(send_email),
            args=(
                current_app._get_current_object(),
                message
            )
        ).start()

        response = {
            'message': 'New registration email sent.'
        }

        return jsonify(response), 200

from quart.

Additionally, this is what I tried to run an event loop on the other thread, but I am still getting the same warning:

def send_email(_app, _loop, message):
    with _app.app_context():
        print('====> sending on a separate thread.')
        asyncio.set_event_loop(_loop)
        _loop.run_until_complete(
            mail.send(message)
        )


@app.route('/test')
class Test(Resource):
    async def get(self):
        message = Message(sender=app.config.get('MAIL_USERNAME'),
                          recipients=[app.config.get('MAIL_USERNAME')],
                          subject='TEST')

        thr = Thread(
            target=copy_current_app_context(send_email),
            args=(
                current_app._get_current_object(),
                asyncio.new_event_loop(),
                message
            )
        ).start()

        response = {
            'message': 'New registration email sent.'
        }

        return jsonify(response), 200

from quart.

Sorry to spam, this technique has failed me as well: https://pgjones.gitlab.io/quart/background_tasks.html

from quart.

Does this work?

from contextvars import copy_context
from functools import partial

async def run_sync(func) -> Any:
    loop = asyncio.get_running_loop()
    return await loop.run_in_executor(
        None, copy_context().run, func,
    )

def send_email(message):
    with app.app_context():
        print('====> sending on a separate thread.')
        mail.send(message)

@app.route('/test')
async def get(self):
    message = Message(
        sender=app.config.get('MAIL_USERNAME'),
        recipients=[app.config.get('MAIL_USERNAME')],
        subject='TEST',
    )
    await run_sync(partial(send_email, message))

If so it will get a lot easier in the next Quart release (if not I need to do some more work).

from quart.

Unfortunately, I get the following:

 File "app.py", line 100, in send_email
    with app.app_context:
AttributeError: __enter__

from quart.

Hmm tricky, this then needs to allow the execution of sync code in a thread surrounded by an async context setup. Does this work?

from contextvars import copy_context
from functools import partial

async def run_sync(func) -> Any:
    loop = asyncio.get_running_loop()
    return await loop.run_in_executor(
        None, copy_context().run, func,
    )

def send_email(message):
    print('====> sending on a separate thread.')
    mail.send(message)

@app.route('/test')
async def get(self):
    message = Message(
        sender=app.config.get('MAIL_USERNAME'),
        recipients=[app.config.get('MAIL_USERNAME')],
        subject='TEST',
    )
    async with app.app_context():
        await run_sync(partial(send_email, message))

I've wrapped the run sync in the app context setup, which should keep it set during the run_sync execution. As run_sync copies the context it should also be available in the send_email function...

from quart.

This works!

Pardon my confusion though, I was under the impression that the intent of the original post was to create a function on a new thread to provide the end user with a response while dealing with the mail server connection asynchronously. With this fix it is still blocking my response. Maybe the confusion stemmed from my choice to make the send mail function synchronous, though I kept getting a never awaited error when attaching it to the thread.

from quart.

Ah, the above solution ensures that the actual sending of the message doesn't block the event loop thereby allowing the app/server to serve other requests concurrently. To achieve a background send you will need to use a background task as well,

from contextvars import copy_context
from functools import partial

async def run_sync(func) -> Any:
    loop = asyncio.get_running_loop()
    return await loop.run_in_executor(
        None, copy_context().run, func,
    )

def send_email(message):
    print('====> sending on a separate thread.')
    mail.send(message)

@app.route('/test')
async def get():
    async def _get():
        message = Message(
            sender=app.config.get('MAIL_USERNAME'),
            recipients=[app.config.get('MAIL_USERNAME')],
            subject='TEST',
        )
        async with app.app_context():
            await run_sync(partial(send_email, message))
    asyncio.ensure_future(_get())
    return "Pending", 201

from quart.

This above code is perfect! Thank you so much for the help.

from quart.