Python program which polls for keyboard events has high CPU usage

Question

I made a program that launches a short script each time a certain key combination is pressed. I am using a thread that utilise pyHook in the following manner:

def logic():
    global running
    hm = HookManager()
    hm.KeyDown = captureF
    hm.HookKeyboard()
    while(running):
        pythoncom.PumpWaitingMessages()
    return

where captureF is a function that tests if the certain key combination is pressed and then if pressed launches the script.

on the main thread i am running a windows tray gui that includes options and exit (upon pressing exit it set the flag running to false, resulting the logic thread to finish).

The problem i am facing right now is that the CPU usage is constantly high when the program is launched (even when the script is not launched), i guess the problem is in the way i am testing for keyboard input but i am not sure how to do it in a more efficient way.

Thanks for the help in advance.

Answer 1

The problem is that your polling hogs the CPU: PumpWaitingMessages checks for messages and returns immediately if no messages (it is non-blocking)

You have to insert some kind of delay. The simplest would be:

import time
while(running):
    pythoncom.PumpWaitingMessages()
    time.sleep(0.01)

1/100th second ensures good reactivity and gives breathing space to the CPU. I'll let you adjust the value. The higher you set the value, the less reactive your polling will be.

However, if you don't need any control on your loop, you could as well use the blocking pythoncom.PumpMessages() call, without a loop.