python threading.local() in different module

Question

I am trying to pass data in threading.local() to functions in different module. Code is something like this:

other_module.py:

import threading

# 2.1  
ll = threading.local()

def other_fn():

 # 2.2    
 ll = threading.local()

 v = getattr(ll, "v", None)
 print(v)

main_module.py:

import threading
import other_module

# 1.1
ll = threading.local()

def main_fn(v):

 # 1.2
 ll = threading.local()

 ll.v = v
 other_fn()


for i in [1,2]:
 t = threading.Thread(target=main_fn, args=(i,))
 t.start()

But none of combinations 1.x - 2.x not working for me. I have found similar question - Access thread local object in different module - Python but reply, marked as answer not working for me too if print_message function located in different module.

Is it possible to pass thread local data between modules without passing it as function argument?

Possible duplicate of [Thread local storage in Python](https://stackoverflow.com/questions/1408171/thread-local-storage-in-python) — Fatemeh Abdollahei, Apr 16 '19 at 10:32
@ShivanshJagga No, i have not. I was hoping it uses OS native TLS, but it is not. So i ended up passing all data i needed as thread function params. — ilya, Apr 17 '19 at 19:46

score 0 · Accepted Answer · answered Nov 25 '19 at 09:10

In a similar situation I ended up doing the following in a separate module:

import threading
from collections import defaultdict

tls = defaultdict(dict)


def get_thread_ctx():
    """ Get thread-local, global context"""
    return tls[threading.get_ident()]

This essentially creates a global variable called tls. Then each thread (based on its identity) gets a key in the global dict. I handle that also as a dict. Example:

class Test(Thread):
    def __init__(self):
        super().__init__()
        # note: we cannot initialize thread local here, since thread 
        # is not running yet

    def run(self):
        # Get thread context
        tmp = get_thread_ctx()
        # Create an app-specific entry
        tmp["probe"] = {}
        self.ctx = tmp["probe"]

        while True:
            ...

Now, in a different module:

def get_thread_settings():
    ctx = get_thread_ctx()
    probe_ctx = ctx.get("probe", None)

    # Get what you need from the app-specific region of this thread
    return probe_ctx.get("settings", {})

Hope it helps the next one looking for something similar

python threading.local() in different module

1 Answers1