RFR: 8339561: The test/jdk/java/awt/Paint/ListRepaint.java may fail after JDK-8327401 [v6]

[Sergey Bylokhov]

On Tue, 4 Mar 2025 21:19:09 GMT, Alexey Ivanov <aivanov at openjdk.org> wrote:

>> I think as of now it should be good enough, why do you think volatile will not help here?
>
>> I think as of now it should be good enough
> 
> That's the problem, the presence of the `volatile` modifier creates a false sense of thread-safety, this is why I'd rather not add it.
> 
>> why do you think volatile will not help here?
> 
> The `volatile` modifier guarantees that a thread which reads from the `volatile` field will see everything that occurred before a (new) reference was written to the `volatile` field. Yet there are no guarantees another thread will see any modifications to fields of the object the reference to which is stored in the `volatile` field.
> 
> And this test does exactly this: it writes a reference into the `currentState` field and then it modifies the fields of the object stored in `currentState`. There are no guarantees that `currentState.setAction(true)` will result in `currentState.getAction()` returning `true`.
> 
> If you also declare `TestState.action` as `volatile` or use `AtomicBoolean`, it could be enough to safely access the `currentState` field from two threads. Other fields are final, so they can't be modified, and therefore they don't change after another thread sees the reference to `TestState` object.

@aivanov-jdk Do you have any other comments?

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/20861#discussion_r2047865655