On Wed, 15 May 2024 18:49:49 GMT, ExE Boss <d...@openjdk.org> wrote:
>> src/java.base/share/classes/jdk/internal/lang/stable/StableValueImpl.java
>> line 240:
>>
>>> 238: }
>>> 239: } finally {
>>> 240: supplying = false;
>>
>> Resetting a stable field is a bad idea. I recommend renaming this to
>> `supplierCalled` or `supplied` so we never transition this false -> true
>
> Yes, according to the `@Stable` annotation’s JavaDoc, this is UB:
> https://github.com/openjdk/jdk/blob/8a4315f833f3700075d65fae6bc566011c837c07/src/java.base/share/classes/jdk/internal/vm/annotation/Stable.java#L74-L80
Fyi what usually happens is that if a stable field or similarly constant-folded
field is promoted to constant, the constant promotion can happen to any of the
previous valid values written.
MethodHandle optimisitically sets a trusted final field this way:
https://github.com/openjdk/jdk/blob/8a4315f833f3700075d65fae6bc566011c837c07/src/java.base/share/classes/java/lang/invoke/MethodHandle.java#L1868-L1870
Also a similar example in user code targeting older Java releases, before JDK
16's strong encapsulation so that enums could have been added by reflection:
https://github.com/MinecraftForge/MinecraftForge/issues/3885#issuecomment-355602542
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PR Review Comment: https://git.openjdk.org/jdk/pull/18794#discussion_r1602125255
