RFR: 8376423: Test javax/swing/plaf/metal/MetalUtils/bug6190373.java failed: ClassCastException: class java.lang.Character cannot be cast to class javax.swing.Painter [v2]

[Alexey Ivanov]

On Tue, 27 Jan 2026 18:09:57 GMT, Phil Race <prr at openjdk.org> wrote:

>> src/java.desktop/share/classes/javax/swing/UIManager.java line 247:
>> 
>>> 245:      */
>>> 246:     private static LAFState getLAFState() {
>>> 247:         return LAF_STATE;
>> 
>> I think you still have to use `synchronized (classLock)`, otherwise `LAF_STATE.initialized` in `isLafStateInitialized` could return a stale value.
>
> The existing code only used that when creating the instance, not when retrieving an already created instance, so I don't see why we'd need to extend the lock to the retrieval.

Indeed, the existing code use the lock only when creating the instance.

Yet there are quite a few places where `synchronized (classLock)` is used. In particular, `maybeInitialize` method.

https://github.com/openjdk/jdk/blob/eb6e74b1fa794bf16f572d5dbce157d1cae4c505/src/java.desktop/share/classes/javax/swing/UIManager.java#L1461-L1468

The logic in `maybeInitialize` will remain thread-safe, yet `SwingAccessor.isLafStateInitialized` can return a stale value of `false`. Thus, `SwingAccessor.getLAFStateAccessor().lafStateIsInitialized()` in `DefaultMetalTheme` can return `false` even after `UIManager` was initialised. I guess this problem existed in the original code, too.

To ensure thread-safe access to the `initialized` flag, the method `UIManager.isLafStateInitialized` has to access the flag inside the `synchronized (classLock)` block.

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PR Review Comment: https://git.openjdk.org/jdk/pull/29437#discussion_r2733775328