How to accept push notifications in a plotly/dash app? - python-3.x

Question

I have a client with an open connection to a server which accepts push notifications from the server. I would like to display the data from the push notifications in a plotly/dash page in near real time.
I've been considering my options as discussed in the documentation page.
If I have multiple push-notification clients running in each potential plotly/dash worker process, then I had to manage de-duplicating events, doable, but bug prone and quirky to code.
The idea solution seems to be to run the push network client on only one process and push those notifications into a dcc.Store objects. I assume I would do that by populating a queue in the push clients async callback, and on a dcc.Interval timer gather any new data in that queue and place it in the dcc.Store object. Then all other callbacks get triggered on the dcc.Store object, possibly in separate python processes.
From the documentation I don't see how I would be guarantee the callback that interacts with the push network client to the main process and ensure it doesn't run on any worker processes. Is this possible? The dcc.Interval documentation doesn't make any mention of this detail.
Is there a way to force the dcc.Interval onto one process, or is that the normal operation under Dash with multiple worker processes? Or is there another recommended approach to handling data from a push notification network client?

Answer 1

An alternative to the Interval component pulling updates at regular intervals could be to use a Websocket component to enable push notifications. Simply add the component to the layout and add a clientside callback that performs the appropriate updates based on the received message,
app.clientside_callback("function(msg){return \"Response from websocket: \" + msg.data;}",
Output("msg", "children"), [Input("ws", "message")])
Here is a complete example using a SocketPool to setup endpoints for sending messages,
import dash_html_components as html
from dash import Dash
from dash.dependencies import Input, Output
from dash_extensions.websockets import SocketPool, run_server
from dash_extensions import WebSocket
# Create example app.
app = Dash(prevent_initial_callbacks=True)
socket_pool = SocketPool(app)
app.layout = html.Div([html.Div(id="msg"), WebSocket(id="ws")])
# Update div using websocket.
app.clientside_callback("function(msg){return \"Response from websocket: \" + msg.data;}",
Output("msg", "children"), [Input("ws", "message")])
# End point to send message to current session.
#app.server.route("/send/<message>")
def send_message(message):
socket_pool.send(message)
return f"Message [{message}] sent."
# End point to broadcast message to ALL sessions.
#app.server.route("/broadcast/<message>")
def broadcast_message(message):
socket_pool.broadcast(message)
return f"Message [{message}] broadcast."
if __name__ == '__main__':
run_server(app)