Python multiprocessing lock example

This post uses A simple example to illustrate the effect of a multiprocessing.Lock in Python.

We will start multiple processes, each of which print the string hello world followed by a process index. The process index just shows the order in which the processes are started. By turning on and off the lock, we see how it affects the printed output.

Here is the code:

If we uncomment the Line 37 that does not use a lock, the output will be scrambled like

hhhheelellelllollooo   wo wowwrorolrrllddld  1
  2
d  3
  0

If we uncomment the Line 38 that uses a lock, the output will be like

hello world  0
hello world  2
hello world  3
hello world  1