Yeah, I just wanted to illustrate the issue with a more realistic example. The thread is often abstracted away by a class or a library. Conclusion: do not abstract it away. :)

I've noticed that the mere fact of using "sys.stderr.write()", without even involving a queue, could cause the problem.

Out of curiosity: my understanding of "sys.stderr" being a "TextIOWrapper" implies it's not thread-safe. Therefore, do you have any idea of which lock is involved in this issue?