Using emit in a background task is not working

[averri]

Using emit in a background task is not working together with Popen. Please refer to the example below. I've tried to use the Popen from Eventlet too with no luck.

Environment: Windows 10
Python: 3.6.4

from subprocess import PIPE, Popen
from flask import Flask
from flask_socketio import SocketIO, emit

app = Flask(__name__)
io = SocketIO(app, async_mode='eventlet')

def emit_docker_logs():
    while True:
        command = ['docker', 'logs', '-f', 'web-server']
        proc = Popen(command, stdout=PIPE, stderr=PIPE, universal_newlines=True)
       
        while proc.poll() is None:
            line = str(proc.stdout.readline(), 'utf-8')
            if line:
                print(line) # This gets printed.
                io.emit('logdata', line) # The client does not receive this line.
        print(proc.stderr.readline())
        io.sleep(10)


if __name__ == '__main__':
    io.start_background_task(target=emit_docker_logs)
    io.run(app)