What language and library to choose for solving the problem of data transfer?

Question

Python

Good time, residents of the Toaster!
Briefly:
The task is essentially to establish some kind of connection with the client, which would allow you to transfer data and know whether the client is online or not.
More meaningful:
There are arrays of data on the client's system, constantly changing at approximately 1 to 120 second intervals. They need to be sent to the web server. It is also important to maintain some kind of connection and know whether the client is online or not. On a NodeJS server with Websocket and Express. It is important to transfer data immediately, i.e. multithreading is needed.
Now I am faced with the question of which language to choose so that it contains:

• Multithreading (there are several data arrays and they are asynchronous)
  
• Having an adequate library for transferring data over websocket (or some other way, but to know whether the client is alive or not, websocket is seductive with the ability to subscribe to updates, which allows you to quickly transfer the task to the client)
  
• *Optional: With support for windows/linux/mac, but may be enough and only windows
  

.
Prompt a sheaf of language and library, please.
Sincerely.

Answer 1

SignalR for C#

Answer 2

C++, Boost.Asio

Answer 3

Something with similar functionality was successfully written on python+asyncio/aiohttp (already mentioned above) and on go. The latter is highly recommended. In my purely personal opinion, the implementation of such tasks on go is a balance between the convenience of writing code and performance / reliability (for example, between python and erlang).