accessing threads continually in tkinter loop

I am trying to make a GUI that continually plot a signal received from a micro processor. I have tried to make this happen by use of classes only, but that failed since only the GUI class was oppend. Now i have implemented threading (or at least I think I have!?) but each thread is only run once. which make me believe that I don't understand how the mainloop in tkinter works, so can I remake my code in away that the threads become active?

import Tkinter
import tkMessageBox as messagebox
from serial import *
from matplotlib.backends.backend_tkagg import FigureCanvasTkAgg
from matplotlib.figure import Figure
import numpy as np
import time
import threading

go=0

x=[0.0001,0.0002,0.0003]
y=[3600,1000,2000]
stid=time.time()

root = Tkinter.Tk()
root.title("Serial gui")

class SensorThread(threading.Thread):
    def run(self):
        global run
        global x
        global y
        global stid
        print "run er ok"
        if go==1:
            print "go er ok"
            ser = Serial(5, 9600, timeout=1)
            f=ser.read(4)
            ser.close()
            x.append(time.time()-stid)
            y.append(f)


class Foo:
    def __init__(self, master):
        print "foo ok"

        frame = Tkinter.Frame(root)

        self.button_left = Tkinter.Button(frame,text="Start",
                                command=self.start)
        self.button_left.pack(side="left")

        self.button_right = Tkinter.Button(frame,text="Stop",
                                command=self.stop)
        self.button_right.pack(side="right")

        self.button_midt = Tkinter.Button(frame, text='Quit', command=self.terminate)
        self.button_midt.pack(side="bottom")

        fig = Figure()
        ax = fig.add_subplot(111, axisbg='black')

        canvas = FigureCanvasTkAgg(fig,master=master)
        canvas.show()
        canvas.get_tk_widget().pack(side='top', fill='both', expand=1)
        frame.pack()

        line1, = ax.plot(x, y, 'r-') # Returns a tuple of line objects, thus the comma
        line1.set_ydata(y)
        fig.canvas.draw()


    def start(self):
        global go
        go=1
        print go

    def stop(self):
        global go
        go=0
        print go

    def terminate(self):
        root.quit()     # stops mainloop
        root.destroy()  # this is necessary on Windows to prevent
                        # Fatal Python Error: PyEval_RestoreThread: NULL tstate

if __name__ == "__main__":
    SensorThread().run()
    Foo(root)
    root.mainloop()

I hope some of you can help my make this code become a program that realtime updates a plot.

Super I have changed the following in the program,

class SensorThread(threading.Thread):
def run(self):
    global run
    global x
    global y
    global stid
    #print "run er ok"
    if go==1:
        print "go er ok"
        ser = Serial(17, 9600, timeout=1)
        f=ser.read(4)
        ser.close()
        x.append(time.time()-stid)
        y.append(f)
        SensorThread().start()
    else:
        SensorThread().start()

class Foo:
....

if __name__ == "__main__":
SensorThread().start()
Foo(root)
root.mainloop()

but it still doesn't update the figure that are plottet, shouldn't it do this in the Foo class? Also now when I exit or quite the python script it still uses 50% of CPU power probably because the Sensor thread now runs for ever!?

Check out this recipe, it shows how to do it:

http://code.activestate.com/recipes/82965-threads-tkinter-and-asynchronous-io/