How to make simultaneous Slack API calls without reinitializing the client?

[hbandlamudi]

• bug
• enhancement (feature request)
• question
• documentation related
• testing related
• discussion

• [x ] I've read and understood the Contributing guidelines and have done my best effort to follow them.
• [x ] I've read and agree to the Code of Conduct.
• [x ] I've searched for any related issues and avoided creating a duplicate issue.

---

Reproducible in:

slackclient version: 2.1.0

python version: 3.7

I created a Slack app (using Flask) using version 1.3.1 and it could handle simultaneous Slack API calls without any issue. Since then, I've tried upgrading to slackclient==2.1.0 and see that when simultaneous calls are made, one of them will fail with the a RunTimeError that the This event loop is already running.

In order to further investigate, I created a simple Flask app which can handle simultaneous calls. The code below works without any issue however if I try to move the loop and slack WebClient initialization outside of the entry() method, simultaneous calls fail. Do these variables need to be reinitialized on each request or is there another way to only initialize them once yet be able to handle concurrent requests?

from flask_api import status
import asyncio
import slack

app = Flask(__name__)
bot_slack_token = 'xoxb-xxxxxxxxxx'

response_headers = {
    'Content-Type': 'application/json'
}

async def send_async_message(channel, text, client):
    response = await client.chat_postMessage(channel=channel, text=text)

    assert response["ok"]
    assert response["message"]["text"] == "ok"


@app.route("/")
def entry():
    asyncio.set_event_loop(asyncio.new_event_loop())
    loop = asyncio.get_event_loop()

    client = slack.WebClient(
        token=bot_slack_token,
        run_async=True
    )

    loop.run_until_complete(send_async_message(channel='#hello', text="ok", client=client)) 

    return make_response("", status.HTTP_200_OK, response_headers)


if __name__ == '__main__':
    app.run(debug=True, host='0.0.0.0')

[SeverinAlexB]

Same problem here

[jeffbuswell]

I'm hitting this issue too. I was able to temporarily work around the problem using nest_asyncio, but a long-term solution would be appreciated.

[hbandlamudi]

@jeffbuswell Could you post an example of how to use nest_asyncio in this situation?

[jeffbuswell]

@hbandlamudi Using your example, it would look something like this:

from flask_api import status
import asyncio
import slack
import nest_asyncio

app = Flask(__name__)
bot_slack_token = 'xoxb-xxxxxxxxxx'
nest_asyncio.apply()

response_headers = {
    'Content-Type': 'application/json'
}

def send_message(channel, text, client):
    response = client.chat_postMessage(channel=channel, text=text)

    assert response["ok"]
    assert response["message"]["text"] == "ok"

@app.route("/")
def entry():
    client = slack.WebClient(
        token=bot_slack_token
    )

    send_message(channel='#hello', text="ok", client=client)

    return make_response("", status.HTTP_200_OK, response_headers)


if __name__ == '__main__':
    app.run(debug=True, host='0.0.0.0')

[hbandlamudi]

@jeffbuswell Thank you for your script. When I tried to use it and initialized client outside of the method, simultaneous calls still fail with RuntimeError: There is no current event loop in thread 'Thread-XX'. so even with nest_asyncio the client would still have to reinitialized at each request.

[RodneyU215]

Hi @hbandlamudi, thanks for opening this issue! If you're looking to make asynchronous requests I wouldn't currently recommend using Flask. Instead I'd use something more async friendly. If you like Flask's API I would use Quart. It uses the exact same API as Flask, but is built for async. Below is a working example of what this would look like:

# example.py
import slack
from quart import Quart

app = Quart(__name__)
bot_slack_token = "xoxb-1234...etc"
client = slack.WebClient(token=bot_slack_token, run_async=True)

async def send_async_message(channel, text, client):
    response = await client.chat_postMessage(channel=channel, text=text)

    assert response["ok"]
    assert response["message"]["text"] == "ok"

@app.route("/")
async def notify():
    await send_async_message(channel="#general", text="ok", client=client)
    return "OK"

if __name__ == "__main__":
    app.run(debug=False)

$ pip install slackclient
$ pip install quart
$ python example.py 

You could also consider aiohttp's web server, but requires slightly more work to get started.

[Marc-Girard]

Quart looks like a great alternative to Flask but it looks like it is Python 3.7 only. My production environment is 3.6 unfortunately.

From the web site:

Quart is only compatible with Python 3.7 or higher and can be installed using pipenv or your favorite python package manager.

[justdave]

I'm running into this as well, but just using the built-in event loop from RTMClient, not an app framework. The nested_asyncio thing fixed it for me as well, but that feels like a hack and not a fix...

[nbeuchat]

Same issue here, I am trying to run the Slack client synchronously with client = slack.WebClient(token=bot_slack_token, run_async=False).

I had to switch back to version 1.3, hopefully, there will be a solution soon

[seratch]

👋 Sorry for the confusion mentioned here. I've created a small test app showing a possible option at this point. https://github.com/slackapi/python-slackclient/blob/master/integration_tests/samples/issues/issue_497.py

As you see, with version 2.0.0 - 2.5.0, using shared WebClient & event_loop. run_until_complete(coro) in Flask (or any similar) applications doesn't work for simultaneous requests. The only workaround is creating a WebClient instance per request as I did in the above test app.

I'm working on addressing this issue (and related others) right now. For the near future, WebClient with run_async=False (the default) will be available for sharing among requests. The fixed version will be the next minor version - 2.6.0. If everything goes well, I'll release the new version by the end of this month.

[seratch]

Let me close this issue now as #662 resolved this for the run_async=False mode.

[seratch]

👋 slackclient 2.6.0rc1 is out. The pre-release version contains fixes for your issue described here.
https://pypi.org/project/slackclient/2.6.0rc1/

One week later from now, we'll be releasing version 2.6.0 to PyPI.

If you have a chance, could you try the release candidate version out and let us know your feedback? Thank you very much for being patient with this issue.