Shared variables and thread.Lock

Question content

In Java, the value of a shared variable in a thread can become stalled unless you use atomic operations or other thread synchronization mechanisms.

Given the GIL in CPython. I see value in Lock inc where: Even in the confusing a = 1 idiom, there are multiple steps performed before the assignment. To prevent race conditions.

But in a case like a = 1, there is no lock. After a thread updates a, is it possible to have threads A and B read different values ​​of a?

Another way to ask this question is, does Lock ensure shared value propagation, whereas the absence of Lock does not?

Correct answer

The problem is not that a = 1. If the only thing you do in your entire code is set a to various values, then you don't need a lock.

However, if you are setting a = 1 while somewhere else in your code is doing a = a 1, then you need to lock them. You lock a = 1 so that if someone else increments a, it will happen exactly before or after you set a.

So in almost all cases, unless you really know what you are doing, a lock is the simplest solution.

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