Access function and stop threading media and servo subprocess in python

Question

I have been doing some searching in this subject and there doesn't seem to be a very clear answer to my question. I currently am working a project where the user clicks on a button and once he does I call a python function, reply(), the function starts two different threads, a (stands for audio) and r (stands for routines) those two threads are supposed to work together and basically point to a direction in the map based as the narrator speaks:

def reply(index, path2, path3):
    a = threading.Thread(target=playaudio(path3))
    r = threading.Thread(target=routine(path2))
    r.start()
    a.start()

I am wondering if there is a way to access the function and stop those threads for both the playaudio and routine functions on user click of a stop button, so that if the user no longer wants to see it, all he needs to do is stop the presentation. The two functions are set up as follows:

# play audio function starts here:
def playaudio(path):
    try:
        subprocess.Popen(["mpg123", path])

    except Exception as ex:
        tkMessageBox.showinfo('Error', 'An error occurred.  ' + str(ex))

# routine function starts here
# routine controls the servo module
def routine(path):
    with open(path, 'rb') as f:
        reader = csv.reader(f)
        settings = list(reader)

    print(settings)
    i = 1
    while i < (len(settings) - 1):
        try:
            setall(int(settings[i][1]), int(settings[i][2]), int(settings[i][3]), int(settings[i][4]))
            delay = float(settings[i+1][0]) - float(settings[i][0]) - 0.015 #includes processing time
            time.sleep(delay)
            i += 1
        except Exception as ex:
            pass
    setall(int(settings[i][1]), int(settings[i][2]), int(settings[i][3]), int(settings[i][4]))

These will be initiated with a Tkinter.Button element on the main screen, and will play both the audio and control the servo module.

button = Tkinter.Button(window, text='Audio 4', command=lambda: reply(1, 'path/to/excel/file.csv', '/path/to/audio/file.mp3'))
button.config(width="30", height="5")
button.place(x=490, y=40)

For the stopping function I thought it would be a solution to add another Tkinter button element but with a different function to quit the subprocess whenever the user clicks on it.

stop_button = Tkinter.Button(window, text='Stop Audio', command=lambda: stop())
stop_button.config(width="30", height="5")
stop_button.place(x=490, y=360)

For the actual stop() function I attempted a few methods such as stop() and destroy() but the either the audio or the servo continue to run, or the actual program shuts off.

So my question is, what should I be doing differently? I would really appreciate any feedback in this problem.

score 1 · Accepted Answer · answered Jun 28 '17 at 18:39

Have you looked into the Queue module? You can send messages to threads with it.

So, presuming you have q (an instance of Queue) which is accessible to your thread functions, your routine() thread function could look something like this:

def routine(path):

    # skip some stuff...

    while i < (len(settings) - 1):
        if not q.empty():
            message = q.get()
            if message == 'stop':
                break

        # rest of your function

In your playaudio() function you'll want to hold onto the Popen object you created and use the `terminate() method to end the process. Take a look at the subprocess documentation for more information on how to do that.

Then, when the user clicks the "stop" button, you can post a message to the queue:

def stop():
    q.put('stop')

As an aside, take look at the multiprocess module too. Python's GIL prevents threading from happening properly, and multiprocess is able to get around that and make use of multiple cores.

That does not seem to work. It actually made the routine function seem to stop working, as I loose all response from my server. Any ideas as to why? — Sam, Jun 29 '17 at 14:32
Look up the documentation for Queue.Queue. You probably actually want to use q.get_nowait() and catch the exception. — Raoul Snyman, Jun 29 '17 at 20:22

Access function and stop threading media and servo subprocess in python

1 Answers1