RFR: 8199149: Improve the exception message thrown by VarHandle of unsupported operation [v2]

[Mandy Chung]

On Wed, 19 Jul 2023 02:19:58 GMT, Mandy Chung <mchung at openjdk.org> wrote:

>> `VarForm::getMemberName` currently throws UOE with no information if the requested access mode is unsupported.   To provide the var handle information, move the access mode check to `VarHandle` so that the exception message can include the var handle information.  Changes include:
>> 
>> 1. change `VarHandle::checkAccessModeThenIsDirect` to check if the access mode is unsupported.  This check is only needed for direct var handle.
>> 2. change `VarHandle::getMethodHandleUncached` to call `getMemberNameOrNull` and throw UOE with an informative exception message if the access mode is unsupported
>> 
>> The error message looks like:
>> 
>> java.lang.UnsupportedOperationException: compareAndSet is not supported for VarHandle[varType=java.lang.String, coord=[class Foo$Goo]]
>
> Mandy Chung has updated the pull request incrementally with one additional commit since the last revision:
> 
>   review feedback

I got feedback from @PaulSandoz.   The patch is updated to include only the access mode information.

`checkAccessModeThenIsDirect` is on a performance sensitive path.   We only need to modify `VarForm::getMemberName` to print out the access mode.   Also mark `getMemberName` as `@Hidden` which then shows the call site from the top of the stack trace.    The user can find out which VarHandle from the callsite from the stack trace location.

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PR Comment: https://git.openjdk.org/jdk/pull/14928#issuecomment-1642902785