help with threading module and passing global variables

[ricardons]

Hi

I'm having a big trouble to get this to work.

I have a function that I want to put in a thread (or multiprocess). This function requires 3 variables.
One of the variables (var_1) is static and no problem passing it through args in the thread module.
The second variable (var_2) changes during the main program

The last variable (flag) i want to use as a trigger when it gets True in the main program.


The "mental" structure of the program should be:

main.py

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import threading from test import function import time   global flag, var_2   var_1 = "var_1"   t = threading.Thread(target=function, args=(var_1,)) t.start()   while True:     var_2 = "var_2 (that changes in each while loop"     flag = True     time.sleep(1)     flag = False

test.py

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def function(var_1):     global var_2, flag     while True:           if flag == True:             print(var_1 + var_2)

But this does not work i think

Someone guru could help me?

[stullis]

First, as a maxim, don't use globals. They're more trouble than they're worth.

Second, you need a thread safe data structure to conduct this operation. "Thread safe" means that the variable can only be accessed by one thread at a time which ensures consistency when any thread uses it. Without thread safety, there may be the possibility of thread1 evaluating the variable, thread 2 changes it, and then thread 1 runs a calculation with the changed variable and gets a nonsensical result. Read up on multithreading locks. Once a lock is implemented, the function will need the variable as an argument.