Exercise 2 of Lesson 8 looks have a potential TOCTOU issue

RE: Exercise 2 of Lesson 8 looks have a potential TOCTOU issue

Rick Cai — Fri, 21 Feb 2025 09:29:49 GMT

I am totally fine as this is a demo to show the usage of mutex and race condition.

Just let learners know how to use these variables correctly.

RE: Exercise 2 of Lesson 8 looks have a potential TOCTOU issue

AHaug — Fri, 21 Feb 2025 09:24:20 GMT

Hi again,

I discussed it with the author and it looks to be as you described, yes. Printing the values by fetching values of increment and decrement count outside mutex lock will still have a race condition as you said. Getting those values added into sum inside mutex will avoid that problem, which you also said.

I will discuss it with the author if it should be updated.

Again thank you for reporting it

Kind regards,
Andreas

RE: Exercise 2 of Lesson 8 looks have a potential TOCTOU issue

Rick Cai — Thu, 20 Feb 2025 14:31:56 GMT

I observed the race condition even with mutex code enabled.

Better to add a notice that "increment_count" + "decrement_count" might not be 40 once mutex is unlocked.

RE: Exercise 2 of Lesson 8 looks have a potential TOCTOU issue

AHaug — Thu, 20 Feb 2025 14:24:58 GMT

Hello,

What you're observing is what is correct. The purpose of the exercise is to show a TOCTOU i.e a race condition.

Kind regards,
Andreas