data.py

class Data:
    __data_instance = None

    @classmethod
    def get_instance(cls):
        if cls.__data_instance is None:
            cls.__data_instance = Data()
        return cls.__data_instance

    def __init__(self):
        self.data = 0
        self.loop = True

server.py

from flask import Flask, jsonify
from multiprocessing import Process
from time import sleep
from data import Data

app = Flask(__name__)

def env_ctr_loop():
    data = Data().get_instance()
    while True:
        if data.loop:
            data.data += 1
        sleep(3)
        print data.data

p = Process(target=env_ctr_loop)
p.start()


@app.route("/")
def hello():
    data = Data().get_instance()
    result = {
        "data.data": data.data
    }
    return jsonify(**result)


@app.route("/start")
def start():
    data = Data().get_instance()
    data.loop = True
    return "Start success"


@app.route("/end")
def end():
    data = Data().get_instance()
    data.loop = False
    return "End success"


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