exit loop on keypress in either Shell/Terminal or variable change

Question

So i'm on my Raspberry pi, and i'm wanting to check to see if a sensor has been activated. I'm potentially running off two different things though, one from a shell that i remote into, and the other off a LCD screen with a couple buttons directly connected to the RPi. I think the best way to do this is to run a loop to see if the user press a key (like the enter key or something) OR if the LCD interface has selected to go on. i'd like to run a loop that check if the user has pressed a key or if a variable has changed somewhere denoting the LCD interface has been changed and then move on with my code, but i don't know the best way to do this. Currently, this is what i have:

import thread
import time
import globals #this is where i keep my project wide global variables. it this this is a good way to do it.... 

try:
    from msvcrt import getch
except ImportError:
    def getch():
        import sys, tty, termios
        fd = sys.stdin.fileno()
        old_settings = termios.tcgetattr(fd)
        try:
            tty.setraw(sys.stdin.fileno())
            ch = sys.stdin.read(1)
        finally:
            termios.tcsetattr(fd, termios.TCSADRAIN, old_settings)
        return ch

char = None

def keypress():
    global char
    char = getch()

thread.start_new_thread(keypress, ())

globals.LCDVar = 0
while True:
    if char is not None:
        print "Key pressed is " + char
        break
    if globals.LCDVar == 1
      break
    time.sleep(.1)
    print "Program is running\n" 

<Run whatever code next>

This works, but i'm not sure what happens to the thread that's created. Does the thread stay alive after i press a key? I if change the variable instead of pressing a key, won't the thread still be there? I would feel comfortable with this if the event would only happen once or twice, but this keypress/varble check might happen 100s or 1000s of times and i don't want to keep starting new threads over and over again.

Is there a better way to do this?

Thanks for any advice!!

Answer 1

The thread you created exits when the function called in start_new_thread returns, so you don't need to worry about it running forever (that's from the official documentation on thread.start_new_thread).

As far as the "best" way to do this, I think that reversing what is run in a separate thread and what is run in the main line of execution would be helpful. That is, do work in a separate thread and wait for a key press in the main thread. That's traditionally how functionality like this is implemented and it reduces some of the complexity of your loop.