Python Gui programming and cpu usage. How does one create an 'idle' or 'throttle' so a piece of code does not consume 100 of the available cpu?

Question

I received a complaint of sluggishness while a friend was testing out a gui I made. Sure enough, looking at Xp's performance monitor, it runs wide open consuming as much cpu as it can. After some digging around stackoverflow, it seems that this is normal expected behavior.

My question is this: Is there a way to limit or throttle the amount of resources a program is allowed to use? I kept the performance monitor visible while I opened a bunch of programs, and for the most part, all 'professional' programs (things like photoshop, sublime text, etc..) all seem to have an 'idle' state. That is, once started, after the initial peak their cpu usage dies down to a small fraction of the processor.

How does one go about limiting a python programs usage, or making it only grab the power when it needs to (like other programs appear to do)?

A slightly truncated version of my main loop:

while True:
            events = pygame.event.get()
            for event in events:
                if event.type == QUIT:
                    if not flags['confirm']:
                        flags['alert'] = 1
                    else:
                        pygame.quit()

                elif event.type == MOUSEBUTTONDOWN:
                    text_box.set_focus(event.button, event.pos)
                    m_numbar.set_focus(event.button, event.pos)
                    # print event.pos 




            if not flags['window_open']:
                screen.blit(combined_bg, (0,0))
                t_button.update(events, screen)

            else:
                screen.blit(combined_blur, (0,0))

            if flags['config']:
                screen.blit(config_window_img, (0,0))
                text_box.update(events)
                text_box.draw(screen)
                m_numbar.update(events)
                m_numbar.draw(screen)
                submit.update(events, screen)
                cancel.update(events, screen)
                check_box.update(events, screen)
            else: 
                text_box.draw(screen)
                m_numbar.draw(screen)

            if flags['alert']:
                flags['window_open'] = True
                screen.blit(alert_dialog, (0,0))
                alert_cancel.update(events, screen)
                alert_confirm.update(events, screen)


            if flags['saving'][0]: 
                if time.time() - flags['saving'][1] < .75:
                    screen.blit(sav_img, (170,170))
                else:
                    flags['window_open'] = False
                    flags['saving'][0] = False


            if flags['currently_doing_thing']:
                if not flags['alert']: 
                    screen.blit(r_tag, (40,10))
                    if check_for_prog():
                        if not flags['prog_open']:
                            makeDir()
                            flags['prog_open'] = True
                            os.startfile("lla_.exe")
                    else:
                        flags['prog_open'] = False
                        if check_for_grab_process():
                            try:
                                os.system("TASKKILL /F /IM lla_.exe")
                            except:
                                pass




            config_button.update(events, screen)
            pygame.display.update()

In addition to Gui programming, is it possible to limit cpu usage on 'normal' tasks? For instance, while 1 will run at 100%cpu. Is there a way to throttle simple cases like this?

This is most definitely not "normal expected behavior" for a GUI program. What GUI toolkit are you using? — Greg Hewgill
– Greg Hewgill, Commented May 24, 2012 at 0:32
@Greg Hewgill - This thread: stackoverflow.com/questions/4449943/…. Gab suggests that it is normal for a script to try to execute as fast as possible. — Zack
– Zack, Commented May 24, 2012 at 0:34
Yes, that's true for a script that actually has work to do. However, a GUI program typically spends 99% (or more) of its time sitting around waiting for the user to click something. — Greg Hewgill
– Greg Hewgill, Commented May 24, 2012 at 0:35
@Greg Hewgill - Oh, sorry! I missed your initial question! I'm using pygame.. Which seemed like a good idea at the time.. — Zack
– Zack, Commented May 24, 2012 at 0:47

Greg Hewgill · Accepted Answer · 2012-05-24 00:52:18Z

3

When using Pygame, your main loop will look something like this (from Python Pygame Introduction):

while 1:
    for event in pygame.event.get():
        if event.type == pygame.QUIT: sys.exit()

    ballrect = ballrect.move(speed)
    if ballrect.left < 0 or ballrect.right > width:
        speed[0] = -speed[0]
    if ballrect.top < 0 or ballrect.bottom > height:
        speed[1] = -speed[1]

    screen.fill(black)
    screen.blit(ball, ballrect)
    pygame.display.flip()

Notice the call to pygame.event.get() at the top of the loop. Under normal circumstances with nothing else happening, this function will block when called. That means that your script will wait for the event.get() function to return, while using no CPU at all. The event.get() function only returns when there is something interesting for you to deal with (mouse move, keypress, etc).

The description of your problem leads me to believe that you're not using pygame.event.get() as it is intended to be used. Perhaps you could show what your main loop looks like.

answered May 24, 2012 at 0:52

Greg Hewgill

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4 Comments

Zack Over a year ago

I've added my code. It looks like it is due to me assigning events to a list, instead of iterating it directly..? Is there a way to manually block a function? Your post is the first I've heard of the term. A quick googling didn't yield much info.

Spencer Rathbun Over a year ago

On a related note, this is why most gui systems are multi thread/process systems. They can do stuff while the user continues pressing buttons without it getting "stuck".

Greg Hewgill Over a year ago

@Zack: At first glance there doesn't seem to be anything wrong with your main loop. You might want to have a look at A Newbie Guide to pygame which discusses pygame events in section 11. Are you calling pygame.event.poll() at all? Perhaps you could try adding a pygame.event.wait() at the top of your loop to see what happens. Finally, I would start with a small example that doesn't use 100% cpu, and use that to find out what you are doing to cause the problem.

Greg Hewgill Over a year ago

@Zack: However, I must say that the code you showed appears to be doing ordinary GUI stuff like dialogs and text boxes. Unless you really need the full control offered by pygame, you're going to end up reimplementing a lot of stuff that is already done for you by higher-level GUI toolkits. For example, Tkinter comes with Python and makes it super easy to build a GUI. Other popular options are wxPython and PyQt.

Ignacio Vazquez-Abrams · Accepted Answer · 2012-05-24 00:40:07Z

0

The idle callback for the GUI loop is always called, unless it is explicitly told not to be called (via the callback itself, usually by returning false). Simply keep it disabled most of the time, and only enable it when an event happens that would require it to run.

answered May 24, 2012 at 0:40

Ignacio Vazquez-Abrams

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