Skip to main content

Polling loops vs blocking calls to Queue

This short code demonstrates how blocking calls to a Queue, while consuming less CPU, are limited in their response time by the minimum time slice the OS is willing to allocate (typically 10ms for Mac OS X and Linux). Non-blocking calls to Pipe, using poll() to check if there is data, on the other hand, give us millisecond or less response times, though they consume more CPU. In this respect doing a blocking call to a CPU is no different than adding sleep(.01) statements to a polling loop. In a way, if you execute a sleep(.01) only when you have no events in your poll you will be more efficient than if you had a blocking call pull events off your Queue one by one - because each call to Queue.get() consumes a time-slice, whereas the sleep(.01) only occurs once.


Popular posts from this blog

Flowing text in inkscape (Poster making)

You can flow text into arbitrary shapes in inkscape. (From a hint here).

You simply create a text box, type your text into it, create a frame with some drawing tool, select both the text box and the frame (click and shift) and then go to text->flow into frame.


The omnipresent anonymous asked:
Trying to enter sentence so that text forms the number three...any ideas?
The solution:
Type '3' using the text toolConvert to path using object->pathSize as necessaryRemove fillUngroupType in actual text in new text boxSelect the text and the '3' pathFlow the text

Drawing circles using matplotlib

Use the pylab.Circle command

import pylab #Imports matplotlib and a host of other useful modules cir1 = pylab.Circle((0,0), radius=0.75, fc='y') #Creates a patch that looks like a circle (fc= face color) cir2 = pylab.Circle((.5,.5), radius=0.25, alpha =.2, fc='b') #Repeat (alpha=.2 means make it very translucent) ax = pylab.axes(aspect=1) #Creates empty axes (aspect=1 means scale things so that circles look like circles) ax.add_patch(cir1) #Grab the current axes, add the patch to it ax.add_patch(cir2) #Repeat

Running a task in a separate thread in a Tkinter app.

Use Queues to communicate between main thread and sub-threadUse wm_protocol/protocol to handle quit eventUse Event to pass a message to sub-threadimport Tkinter as tki, threading, Queue, time def thread(q, stop_event): """q is a Queue object, stop_event is an Event. stop_event from """ while(not stop_event.is_set()): if q.empty(): q.put(time.strftime('%H:%M:%S')) class App(object): def __init__(self): self.root = tki.Tk() = tki.Text(self.root, undo=True, width=10, height=1)'left') self.queue = Queue.Queue(maxsize=1) self.poll_thread_stop_event = threading.Event() self.poll_thread = threading.Thread(target=thread, name='Thread', args=(self.queue,self.poll_thread_stop_event)) self.poll_thread.start() self.poll_interval = 250 self.poll() self.root.wm_protocol("WM_DELETE…