gtk progressbar doesn't work anymore after matplot event? - multithreading

Question

Hi I'm new at programming in python and gtk.
I'm writing a program to do some measurement.
For plotting the measurement, I use matplotlib.
The program will have a function to turn a heater on and off and to make the measurement.
I want to use separate threads for the heater and the measurement.
For now the communication with the hardware hasn't been implemented yet in this program.
The problem is when I click the "measurebutton", the "progressbar" doesn't work anymore.
I get a message:
gtk.ProgressBar object at 0x29b8460 (uninitialized at 0x0)
When I only use the heaterbutton, the progressbar keeps working
What am I doing wrong ?
This is the code
#!/usr/bin/env python
import pygtk
pygtk.require('2.0')
import gtk
import time
import gobject
import threading
import matplotlib
import numpy as np
from matplotlib.backends.backend_gtkagg import FigureCanvasGTKAgg as FigureCanvas
class measure:
# callback to quit
def delete_event(self, widget, event, data = None):
gtk.main_quit()
return False
def heater_helper(self, widget, heater, progressbar):
print "starting heater thread"
threading.Thread(target=self.heater_cb, args=(widget, heater, progressbar)).start()
def heater_cb(self, widget, heater, progressbar):
heaterstring = "6.3"
heater = eval(heaterstring)
stap = 1
j = 0.1
heatervalue = widget.get_active()
print heatervalue
progressbar.set_fraction(0.1)
while (stap <= 10 ):
if widget.get_active():
print widget.get_active()
fraction = j * stap
print fraction
progressbar.set_fraction(fraction)
stap = stap + 1
time.sleep(1)
else:
stap = 11
progressbar.set_fraction(0.0)
break
def do_measurement_helper(self, widget, fig):
print " Start measurement thread"
threading.Thread(target=self.do_measurement, args=(widget, fig)).start()
def do_measurement(self, widget, fig):
fig.clear()
ax = fig.add_subplot(111)
x = np.arange(0, 5*np.pi, 0.01)
y = np.sin(x**2)*np.exp(-x)
ax.plot(x, y)
fig.canvas.draw()
def __init__(self):
# Create new Window
self.window = gtk.Window(gtk.WINDOW_TOPLEVEL)
self.window.connect("delete_event", self.delete_event)
self.window.show()
mainbox = gtk.HBox(False, 0)
self.window.add(mainbox)
mainbox.show()
leftvbox = gtk.VBox(False, spacing = 10)
mainbox.pack_start(leftvbox, expand = False, fill = False, padding = 0)
leftvbox.show()
rightvbox = gtk.VBox(False, spacing = 10)
mainbox.pack_start(rightvbox, expand = False, fill = False, padding =0)
rightvbox.show()
heaterprogressbar = gtk.ProgressBar()
leftvbox.pack_start(heaterprogressbar, expand = False, fill = False, padding = 0)
heaterprogressbar.show()
heaterbutton = gtk.ToggleButton("Heater")
leftvbox.pack_start(heaterbutton, expand = True, fill = False, padding = 0)
heaterbutton.show()
heaterbutton.connect("toggled", self.heater_helper, heaterbutton, heaterprogressbar)
fig = matplotlib.figure.Figure(figsize=(5,4), dpi=64)
canvas = FigureCanvas(fig)
rightvbox.pack_start(canvas, expand = True, fill = True, padding = 0 )
canvas.show()
measurebutton = gtk.Button("Measure")
rightvbox.pack_start(measurebutton, expand = False, fill = False, padding = 0)
measurebutton.show()
measurebutton.connect("clicked", self.do_measurement_helper, fig)
def main():
gtk.main()
return(0)
if __name__ == "__main__":
gtk.gdk.threads_init()
measure()
main()
gtk.gdk.threads_leave()
Kind regards,
Joris Weijters

Answer 1

Combining threads, Matplotlib, and the GTK main loop is probably not supported and difficult to debug exactly what is going on. My advice is not to do any GUI calls from threads, but instead schedule them using gobject.idle_add().

Answer 2

Threads, Matplotlib and the GTK main loop can be combined, if you keep in mind some things:
I use gobject.threads_init() instead of gtk.gdk.threads_init(), the gtk.gdk variant did not work for me in combination with Matplotlib. I think you can also omit the gtk.gdk.threads_leave().
As ptomato mentioned, you should let the main gtk thread handle anything that has to do with gtk widgets by calling the gobject.idle_add() and gobject.timeout_add() functions.
I usually make a helper function to periodically update the statusbar from a float variable:
def do_measurement(self):
self.data = []
self.progress = 0
self.abort = threading.Event()
gobject.timeout_add(100, self.update_progressbar)
for point in some_generator_yielding_100_values():
if self.abort.is_set():
break
self.data.append(point)
self.progress += 0.01
self.progress = None
def update_progressbar(self):
if self.progress is None:
self.progressbar.set_fraction(0) # reset bar
return False # do not run again
self.progressbar.set_fraction(self.progress)
return True # run again after 100ms
def start_measurement(self):
threading.Thread(target=self.do_measurement).start()
def stop_measurement(self):
self.abort.set()
But you can of course also just call gobject.idle_add(self.progressbar.set_fraction, x) to set the new value x asynchroneously.