Asynchronous Streaming To Embedded Bokeh Server

Question

The question: My python application starts a Bokeh server as described in this article:

http://matthewrocklin.com/blog/work/2017/06/28/simple-bokeh-server

now, I want to visualize streaming data, which is generated in the python application, which started the bokeh server and push it asynchronously to my bokeh visualization. Is this possible? How?

Answer 1

Yes it is possible. I think the best option is to have a separate thread that fills the data-bucket and on the other side the Bokeh periodic update function (like in example you mentioned) that accesses that data and streams it to the browser. See this simple example below. But have also a look at Bokeh documentation about updating plot data from threads.

import random, time
from tornado.ioloop import IOLoop
from bokeh.server.server import Server
from bokeh.application import Application
from bokeh.application.handlers.function import FunctionHandler
from bokeh.plotting import figure, ColumnDataSource
from threading import Thread

class BokehApp():
    plot_data = []
    last_data_length = None

    def __init__(self):
        thread = Thread(target = self.startDataAcquisition)
        thread.start()

        io_loop = IOLoop.current()
        server = Server(applications = {'/myapp': Application(FunctionHandler(self.make_document))}, io_loop = io_loop, port = 5001)
        server.start()
        server.show('/myapp')
        io_loop.start()

    def startDataAcquisition(self):
        while True:
            self.plot_data.append({'x': [random.random()], 'y': [random.random()], 'color': [random.choice(['red', 'blue', 'green'])]})
            time.sleep(5)

    def make_document(self, doc):
        source = ColumnDataSource({'x': [], 'y': [], 'color': []})
        fig = figure(title = 'Streaming Circle Plot!', sizing_mode = 'scale_both')
        fig.circle(source = source, x = 'x', y = 'y', color = 'color', size = 10)

        def update():
            if self.last_data_length is not None and self.last_data_length != len(self.plot_data):
                source.stream(self.plot_data[-1])
            self.last_data_length = len(self.plot_data)

        doc.add_root(fig)
        doc.add_periodic_callback(update, 1000)

if __name__ == '__main__':
    app = BokehApp()